Document and Entity Information Document - USD ($)	12 Months Ended
Document and Entity Information Document - USD ($)	Dec. 31, 2017	Feb. 14, 2018	Jun. 30, 2017
DEI [Abstract]
Entity Registrant Name	INTERPUBLIC GROUP OF COMPANIES, INC.
Entity Central Index Key	0000051644
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	1217
Document Fiscal Period Focus	FY
Amendment Flag	false
Trading Symbol	IPG
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Common Stock, Shares Outstanding		384,469,632
Entity Public Float			$ 9,694,530,139

Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
REVENUE	$ 7,882.4	$ 7,846.6	$ 7,613.8
OPERATING EXPENSES:
Salaries and related expenses	5,068.1	5,035.1	4,854.8
Office and general expenses	1,840.7	1,870.5	1,884.2
Total operating expenses	6,908.8	6,905.6	6,739.0
OPERATING INCOME	973.6	941.0	874.8
EXPENSES AND OTHER INCOME:
Interest expense	(90.8)	(90.6)	(85.8)
Interest income	19.4	20.1	22.8
Other expense, net	(26.2)	(40.3)	(49.6)
Total (expenses) and other income	(97.6)	(110.8)	(112.6)
Income before income taxes	876.0	830.2	762.2
Provision for income taxes	281.9	198.0	282.8
Income of consolidated companies	594.1	632.2	479.4
Equity in net income of unconsolidated affiliates	0.9	0.3	1.1
NET INCOME	595.0	632.5	480.5
Net income attributable to noncontrolling interests	(16.0)	(24.0)	(25.9)
NET INCOME AVAILABLE TO IPG COMMON STOCKHOLDERS	$ 579.0	$ 608.5	$ 454.6
Earnings per share available to IPG common stockholders:
Basic	$ 1.49	$ 1.53	$ 1.11
Diluted	$ 1.46	$ 1.49	$ 1.09
Weighted-average number of common shares outstanding:
Basic	389.6	397.9	408.1
Diluted	397.3	408.0	415.7
Dividends declared per common share	$ 0.72	$ 0.60	$ 0.48

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
NET INCOME	$ 595.0	$ 632.5	$ 480.5
Foreign Currency Translation:
Foreign currency translation adjustments	132.2	(55.9)	(256.8)
Reclassification adjustments recognized in net income	1.1	3.7	23.3
Foreign currency translation, net of tax	133.3	(52.2)	(233.5)
Available-for-sale securities:
Changes in fair value of available-for-sale securities	0.0	0.5	0.5
Recognition of previously unrealized gains in net income	(0.7)	(1.3)	0.0
Income tax effect	0.1	0.1	0.0
Available-for-sale securities, net of tax	(0.6)	(0.7)	0.5
Derivatives instruments:
Recognition of previously unrealized losses included in net income	2.1	2.0	2.0
Income tax effect	(0.5)	(0.8)	(0.7)
Derivative instruments, net of tax	1.6	1.2	1.3
Defined benefit pension and other postretirement plans:
Net actuarial (losses) gains for the period	(13.6)	(85.4)	14.2
Amortization of unrecognized losses, transition obligation and prior service cost included in net income	6.9	5.4	10.6
Less: settlement and curtailment losses (gains) included in net income	6.8	0.4	(0.2)
Other	2.7	(2.0)	0.4
Income tax effect	(0.5)	15.3	(6.4)
Defined benefit pension and other postretirement plans, net of tax	2.3	(66.3)	18.6
Other comprehensive income (loss), net of tax	136.6	(118.0)	(213.1)
Total comprehensive income	731.6	514.5	267.4
Less: comprehensive income attributable to noncontrolling interests	17.5	22.9	21.7
Comprehensive Income Attributable to IPG	$ 714.1	$ 491.6	$ 245.7

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
ASSETS:
Cash and cash equivalents	$ 790.9	$ 1,097.6
Accounts receivable, net of allowance of $42.7 and $55.7, respectively	4,585.0	4,389.7
Expenditures billable to clients	1,747.4	1,518.1
Assets held for sale	5.7	203.2
Other current assets	335.1	229.4
Total current assets	7,464.1	7,438.0
Property and equipment, net	650.4	622.0
Deferred income taxes	236.0	220.3
Goodwill	3,820.4	3,674.4
Other non-current assets	524.3	530.5
TOTAL ASSETS	12,695.2	12,485.2
LIABILITIES:
Accounts payable	6,907.8	6,303.6
Accrued liabilities	674.7	794.0
Short-term borrowings	84.9	85.7
Current portion of long-term debt	2.0	323.9
Liabilities held for sale	8.8	198.8
Total current liabilities	7,678.2	7,706.0
Long-term debt	1,285.6	1,280.7
Deferred compensation	476.6	480.7
Other non-current liabilities	766.9	708.3
TOTAL LIABILITIES	10,207.3	10,175.7
Redeemable noncontrolling interests (see Note 4)	252.1	252.8
STOCKHOLDERS' EQUITY:
Common stock, $0.10 par value, shares authorized: 800.0 shares issued: 2017 – 386.2; 2016 – 394.3 shares outstanding: 2017 – 383.2; 2016 – 391.6	38.6	39.4
Additional paid-in capital	955.2	1,199.2
Retained earnings	2,093.6	1,804.3
Accumulated other comprehensive loss, net of tax	(827.4)	(962.5)
Stockholders Equity Subtotal Before Treasury Stock	2,260.0	2,080.4
Less: Treasury stock, at cost: 2017 – 3.0 shares; 2016 – 2.7 shares	(59.0)	(63.3)
Total IPG stockholders' equity	2,201.0	2,017.1
Noncontrolling interests	34.8	39.6
TOTAL STOCKHOLDERS' EQUITY	2,235.8	2,056.7
TOTAL LIABILITIES AND EQUITY	$ 12,695.2	$ 12,485.2

Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Millions, $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 42.7	$ 55.7
Common stock, par value	$ 0.10	$ 0.10
Common stock, shares authorized	800.0	800.0
Common stock, shares issued	386.2	394.3
Common stock, shares outstanding	383.2	391.6
Treasury stock, shares	3.0	2.7

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 595.0	$ 632.5	$ 480.5
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of fixed assets and intangible assets	157.1	160.2	157.0
Provision for uncollectible receivables	9.5	16.7	11.4
Amortization of restricted stock and other non-cash compensation	82.0	85.6	70.3
Net amortization of bond discounts and deferred financing costs	5.8	5.6	5.8
Deferred income tax provision	1.1	45.7	49.5
Net losses on sales of businesses	24.1	41.4	50.1
Other	12.7	35.5	24.2
Changes in assets and liabilities, net of acquisitions and divestitures, providing (using) cash:
Accounts receivable	37.6	(220.7)	(236.1)
Expenditures billable to clients	(165.5)	(2.2)	(237.8)
Other current assets	27.4	(4.8)	(9.7)
Accounts payable	311.9	(126.1)	419.0
Accrued liabilities	(241.3)	(61.1)	(35.3)
Other non-current assets and liabilities	24.4	(95.5)	(60.4)
Net cash provided by operating activities	881.8	512.8	688.5
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures	(155.9)	(200.7)	(161.1)
Acquisitions, net of cash acquired	(30.6)	(52.0)	(28.6)
Other investing activities	(9.7)	(11.2)	(10.0)
Net cash used in investing activities	(196.2)	(263.9)	(199.7)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repayments of long-term debt	(324.6)	(1.8)	(2.0)
Repurchases of common stock	(300.1)	(303.3)	(285.2)
Common stock dividends	(280.3)	(238.4)	(195.5)
Acquisition-related payments	(53.7)	(40.8)	(53.1)
Tax payments for employee shares withheld	(38.8)	(23.1)	(17.6)
Distributions to noncontrolling interests	(20.4)	(13.7)	(15.9)
Exercise of stock options	13.1	10.2	13.5
Net increase (decrease) in short-term borrowings	3.0	(56.2)	51.8
Excess tax benefit on share-based compensation	0.0	0.0	10.2
Other financing activities	(3.1)	0.7	2.9
Net cash used in financing activities	(1,004.9)	(666.4)	(490.9)
Effect of foreign exchange rate changes on cash, cash equivalents and restricted cash	16.8	11.6	(156.2)
Net decrease in cash, cash equivalents and restricted cash	(302.5)	(405.9)	(158.3)
Cash, cash equivalents and restricted cash at beginning of period	1,100.2	1,506.1	1,664.4
Cash, cash equivalents and restricted cash at end of period	$ 797.7	$ 1,100.2	$ 1,506.1

Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Additional Paid-In Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Loss, Net of Tax	Treasury Stock	Total IPG Stockholders' Equity	Noncontrolling Interests
Balance at Dec. 31, 2014	$ 2,151.2	$ 41.2	$ 1,547.5	$ 1,183.3	$ (636.7)	$ (19.0)	$ 2,116.3	$ 34.9
Balance, shares at Dec. 31, 2014		412.8
Net income	480.5			454.6			454.6	25.9
Other comprehensive income	(213.1)				(208.9)		(208.9)	(4.2)
Reclassifications related to redeemable noncontrolling interests	(6.0)							(6.0)
Distributions to noncontrolling interests	(15.9)							(15.9)
Change in redemption value of redeemable noncontrolling interests	(3.9)			(3.9)			(3.9)
Repurchases of common stock	(285.2)					(285.2)	(285.2)
Retirement of treasury stock, shares		(11.3)
Retirement of treasury stock	0.0	$ (1.2)	(232.0)			233.2	0.0
Common stock dividends	(195.5)			(195.5)			(195.5)
Stock-based compensation, shares		2.4
Stock-based compensation, Value	83.4	$ 0.3	83.1				83.4
Exercise of stock options, shares		1.3
Exercise of stock options, Value	13.7	$ 0.2	13.5				13.7
Shares withheld for taxes, shares		(0.8)
Shares withheld for taxes, Value	(17.8)	$ (0.1)	(17.7)				(17.8)
Excess tax benefit from stock-based compensation	10.2		10.2				10.2
Other	0.2		(0.5)	(0.9)			(1.4)	1.6
Balance, shares at Dec. 31, 2015		404.4
Balance at Dec. 31, 2015	2,001.8	$ 40.4	1,404.1	1,437.6	(845.6)	(71.0)	1,965.5	36.3
Net income	632.5			608.5			608.5	24.0
Other comprehensive income	(118.0)				(116.9)		(116.9)	(1.1)
Reclassifications related to redeemable noncontrolling interests	(5.8)							(5.8)
Distributions to noncontrolling interests	(13.7)							(13.7)
Change in redemption value of redeemable noncontrolling interests	(2.1)			(2.1)			(2.1)
Repurchases of common stock	(303.3)					(303.3)	(303.3)
Retirement of treasury stock, shares		(13.7)
Retirement of treasury stock	0.0	$ (1.4)	(309.6)			311.0	0.0
Common stock dividends	(238.4)			(238.4)			(238.4)
Stock-based compensation, shares		3.5
Stock-based compensation, Value	117.1	$ 0.4	116.7				117.1
Exercise of stock options, shares		1.2
Exercise of stock options, Value	10.3	$ 0.1	10.2				10.3
Shares withheld for taxes, shares		(1.1)
Shares withheld for taxes, Value	(23.3)	$ (0.1)	(23.2)				(23.3)
Other	(0.4)		(1.0)	(1.3)			(0.3)	(0.1)
Balance, shares at Dec. 31, 2016		394.3
Balance at Dec. 31, 2016	2,056.7	$ 39.4	1,199.2	1,804.3	(962.5)	(63.3)	2,017.1	39.6
Net income	595.0			579.0			579.0	16.0
Other comprehensive income	136.6				135.1		135.1	1.5
Reclassifications related to redeemable noncontrolling interests	0.6		(0.3)				(0.3)	0.9
Distributions to noncontrolling interests	(20.9)							(20.9)
Change in redemption value of redeemable noncontrolling interests	(7.9)			(7.9)			(7.9)
Repurchases of common stock	(300.1)					(300.1)	(300.1)
Retirement of treasury stock, shares		(13.4)
Retirement of treasury stock	0.0	$ (1.3)	(303.1)			304.4	0.0
Common stock dividends	(280.3)			(280.3)			(280.3)
Stock-based compensation, shares		5.7
Stock-based compensation, Value	87.0	$ 0.6	86.4				87.0
Exercise of stock options, shares		1.2
Exercise of stock options, Value	13.2	$ 0.1	13.1				13.2
Shares withheld for taxes, shares		(1.6)
Shares withheld for taxes, Value	(39.0)	$ (0.2)	(38.8)				(39.0)
Other	(5.1)		(1.3)	(1.5)			(2.8)	(2.3)
Balance, shares at Dec. 31, 2017		386.2
Balance at Dec. 31, 2017	$ 2,235.8	$ 38.6	$ 955.2	$ 2,093.6	$ (827.4)	$ (59.0)	$ 2,201.0	$ 34.8

Significant Accounting Policies (Notes)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Business Description

The Interpublic Group of Companies, Inc. and subsidiaries (the “Company,” “IPG,” “we,” “us” or “our”) is one of the world’s premier global advertising and marketing services companies. Our agencies create customized marketing programs for clients that range in scale from large global marketers to regional and local clients. Comprehensive global services are critical to effectively serve our multinational and local clients in markets throughout the world, as they seek to build brands, increase sales of their products and services and gain market share.

Principles of Consolidation

The Consolidated Financial Statements include the accounts of the Company and its consolidated subsidiaries, some of which are not wholly owned. Investments in companies over which we do not have control, but have the ability to exercise significant influence, are accounted for using the equity method of accounting. Investments in companies over which we have neither control nor have the ability to exercise significant influence are accounted for under the cost method. All intercompany accounts and transactions have been eliminated in consolidation.

We have consolidated certain entities meeting the definition of variable interest entities, and the inclusion of these entities does not have a material impact on our Consolidated Financial Statements.

Reclassifications

Certain reclassifications and immaterial revisions have been made to the prior period financial statements to conform to the current-year presentation.

We plan to adopt a new presentation for our Consolidated Statements of Operations beginning the first quarter of 2018 which will separately present Cost of services; Selling, general and administrative expenses; and Depreciation and amortization within our Operating expenses. For the years ended December 31, 2017 and 2016, our Selling, general and administrative expenses were $118.6 and $138.8, respectively, which are primarily the expenses of our “Corporate and other” group, as disclosed further in Note 12, excluding depreciation and amortization. For the years ended December 31, 2017 and 2016, Depreciation and amortization were $157.1 and $160.2, respectively, which is also presented on the Consolidated Statements of Cash Flows. This change in presentation of expenses does not impact total operating expenses or operating income.

Use of Estimates

The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) requires us to make judgments, assumptions and estimates that affect the amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the reporting date and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from these estimates and assumptions.

Revenue Recognition

Our revenues are primarily derived from the planning and execution of multi-channel advertising, marketing and communications programs around the world. Our revenues are directly dependent upon the advertising, marketing and corporate communications requirements of our existing clients and our ability to win new clients. Our revenue is typically lowest in the first quarter and highest in the fourth quarter. This reflects the seasonal spending of our clients, incentives earned at year end on various contracts and project work that is typically completed during the fourth quarter.

Most of our client contracts are individually negotiated and, accordingly, the terms of client engagements and the bases on which we earn commissions and fees vary significantly. As is customary in the industry, our contracts generally provide for termination by either party on relatively short notice, usually 90 days.

Our client contracts are complex arrangements that may include provisions for incentive compensation and vendor rebates and credits. Our largest clients are multinational entities and, as such, we often provide services to these clients out of multiple offices and across many of our agencies. In arranging for such services, it is possible that we will enter into global, regional and local agreements. Agreements of this nature are reviewed by legal counsel to determine the governing terms to be followed by the offices and agencies involved.

Revenue for our services is recognized when all of the following criteria are satisfied: (i) persuasive evidence of an arrangement exists; (ii) the price is fixed or determinable; (iii) collectability is reasonably assured; and (iv) services have been performed. Depending on the terms of a client contract, fees for services performed can be recognized in three principal ways: proportional performance (input or output), straight-line (or monthly basis) or completed contract.

•

Fees are generally recognized as earned based on the proportional performance input method of revenue recognition in situations where our fee is reconcilable to the actual hours incurred to service the client as detailed in a contractual staffing plan, where the fee is earned on a per hour basis or where actual hours incurred are provided to the client on a periodic basis (whether or not the fee is reconcilable), with the amount of revenue recognized in these situations limited to the amount realizable under the client contract. We believe an input-based measure (the ‘hour’) is appropriate in situations where the client arrangement essentially functions as a time and out-of-pocket expense contract and the client receives the benefit of the services provided throughout the contract term.


•	Fees are recognized on a straight-line or monthly basis when service is provided essentially on a pro-rata basis and the terms of the contract support monthly basis accounting.

•

Certain fees (such as for major marketing events) are deferred until contract completion if the final act is so significant in relation to the service transaction taken as a whole or if any of the terms of the contract do not otherwise qualify for proportional performance or monthly basis recognition. Fees may also be deferred and recognized upon delivery of a project if the terms of the client contract identify individual discrete projects.

Depending on the terms of the client contract, revenue is derived from diverse arrangements involving fees for services performed, commissions, performance incentive provisions and combinations of the three. Commissions are generally earned on the date of the broadcast or publication. Contractual arrangements with clients may also include performance incentive provisions designed to link a portion of our revenue to our performance relative to either qualitative or quantitative goals, or both. Performance incentives are recognized as revenue for quantitative targets when the target has been achieved and for qualitative targets when confirmation of the incentive is received from the client.

The majority of our revenue is recorded as the net amount of our gross billings less pass-through expenses charged to a client. In most cases, the amount that is billed to clients significantly exceeds the amount of revenue that is earned and reflected in our Consolidated Financial Statements because of various pass-through expenses, such as production and media costs. We assess whether our agency or the third-party supplier is the primary obligor, and we evaluate the terms of our client agreements as part of this assessment. In addition, we give appropriate consideration to other key indicators such as latitude in establishing price, discretion in supplier selection and credit risk to the vendor. Because we operate broadly as an advertising agency, based on our primary lines of business and given the industry practice to generally record revenue on a net versus gross basis, we believe that there must be strong evidence in place to overcome the presumption of net revenue accounting. Accordingly, we generally record revenue net of pass-through charges as we believe the key indicators of the business suggest we generally act as an agent on behalf of our clients in our primary lines of business. In those businesses where the key indicators suggest we act as a principal (primarily sales promotion and event, sports and entertainment marketing), we record the gross amount billed to the client as revenue and the related incremental direct costs incurred as office and general expenses. In general, we also report revenue net of taxes assessed by governmental authorities that are directly imposed on our revenue-producing transactions.

As we provide services as part of our core operations, we generally incur incidental expenses, which, in practice, are commonly referred to as “out-of-pocket” expenses. These expenses often include expenses related to airfare, mileage, hotel stays, out-of-town meals and telecommunication charges. We record the reimbursements received for such incidental expenses as revenue with a corresponding offset to office and general expense.

We receive credits from our vendors and media outlets for transactions entered into on behalf of our clients that, based on the terms of our contracts and local law, are either remitted to our clients or retained by us. If amounts are to be passed through to clients, they are recorded as liabilities until settlement or, if retained by us, are recorded as revenue when earned.

Cash and Cash Equivalents

Cash equivalents are highly liquid investments, which include certificates of deposit, government securities, commercial paper and time deposits with original maturities of three months or less at the time of purchase and are stated at estimated fair value, which approximates cost. Cash is maintained at multiple high-credit-quality financial institutions.

Allowance for Doubtful Accounts

The allowance for doubtful accounts is estimated based on the aging of accounts receivable, reviews of client credit reports, industry trends and economic indicators, as well as reviews of recent payment history for specific customers. The estimate is based largely on a formula-driven calculation but is supplemented with economic indicators and knowledge of potential write-offs of specific client accounts.

Expenditures Billable to Clients

Expenditures billable to clients are primarily comprised of production and media costs that have been incurred but have not yet been billed to clients, as well as fees that have been earned which have not yet been billed to clients. Unbilled amounts are presented in expenditures billable to clients regardless of whether they relate to our fees or production and media costs. A provision is made for unrecoverable costs as deemed appropriate.

Accounts Payable

Accounts payable includes all operating payables, including those related to all media and production costs. These payables are due within one year.

Investments

Our investments in short-term marketable securities include investment-grade time deposits, commercial paper, government securities with maturities greater than three months but less than twelve months and publicly traded companies over which we do not exert a significant influence. These investments are classified as available-for-sale and reported at fair value based on quoted market prices with net unrealized gains and losses reported as a component of accumulated other comprehensive loss. Our non-publicly traded investments and all other publicly traded investments, including investments to fund certain deferred compensation and retirement obligations, are accounted for using the equity method or cost method. We do not disclose the fair value for all equity method investments or investments held at cost as it is not practical to estimate fair value since there is no readily available market data and it is cost prohibitive to obtain independent valuations. We regularly review our equity and cost method investments to determine whether a significant event or change in circumstances has occurred that may impact the fair value of each investment. In the event a decline in fair value of an investment occurs, we determine if the decline has been other-than-temporary. We consider our investments strategic and long-term in nature, so we determine if the fair value decline is recoverable within a reasonable period. For our investments, we evaluate fair value based on specific information (valuation methodologies, estimates of appraisals, financial statements, etc.) in addition to quoted market price, if available. We consider all known quantitative and qualitative factors in determining if an other-than-temporary decline in value of an investment has occurred.

Derivatives

We are exposed to market risk related to interest rates, foreign currency rates and certain balance sheet items. From time to time we enter into derivative instruments for risk management purposes, and not for speculative purposes. All derivative instruments are recorded at fair value on our balance sheet. Changes in fair value are immediately included in earnings if the derivatives are not designated as a hedge instrument or if the derivatives do not qualify as effective hedges. For derivatives designated as hedge instruments, we evaluate for hedge accounting both at inception and throughout the hedge period. If a derivative is designated as a fair value hedge, then changes in the fair value of the derivative are offset against the changes in the fair value of the underlying hedged item. If a derivative is designated as a cash flow hedge, then the effective portion of the changes in the fair value of the derivative is recognized as a component of accumulated other comprehensive income and subsequently reclassified to earnings in our Consolidated Statement of Operations in the same period as the underlying hedged transaction affects earnings.

Property and Equipment

Furniture, equipment, leasehold improvements and buildings are stated at cost, net of accumulated depreciation. Furniture and equipment are depreciated generally using the straight-line method over the estimated useful lives of the related assets, which range from 3 to 7 years for furniture and equipment, 10 to 35 years for buildings and the shorter of the useful life or the remaining lease term for leasehold improvements. Land is stated at cost and is not depreciated.

We capitalize certain internal and external costs incurred to acquire or create internal use software, principally related to our enterprise resource planning (“ERP”) systems. Our ERP systems are stated at cost, net of accumulated amortization, and are amortized using the straight-line method over 10 years. All other internal use computer software are stated at cost, net of accumulated amortization and are amortized using the straight-line method over the estimated useful lives of the related assets, which range from 3 to 7 years.

Goodwill and Other Intangible Assets

We account for our business combinations using the acquisition accounting method, which requires us to determine the fair value of net assets acquired and the related goodwill and other intangible assets. Determining the fair value of assets acquired and liabilities assumed requires management's judgment and involves the use of significant estimates, including projections of future cash inflows and outflows, discount rates, asset lives and market multiples. Considering the characteristics of advertising, specialized marketing and communication services companies, our acquisitions usually do not have significant amounts of tangible assets, as the principal asset we typically acquire is creative talent. As a result, a substantial portion of the purchase price is allocated to goodwill and other intangible assets.

We review goodwill and other intangible assets with indefinite lives not subject to amortization as of October 1^st each year and whenever events or significant changes in circumstances indicate that the carrying value may not be recoverable. We evaluate the recoverability of goodwill at a reporting unit level. We have 11 reporting units that were subject to the 2017 annual impairment testing. Our annual impairment review as of October 1, 2017 did not result in an impairment charge for any of our reporting units.

For reporting units not included in the qualitative assessment, or for any reporting units identified in the qualitative assessment as "more likely than not" that the fair value is less than its carrying value, the quantitative impairment test is performed. For our annual impairment test, we compare the respective fair value of our reporting units' equity to the carrying value of their net assets. The sum of the fair values of all our reporting units is also reconciled to our current market capitalization plus an estimated control premium. Goodwill allocated to a reporting unit whose fair value is equal to or greater than its carrying value is not impaired, and no further testing is required. Should the carrying amount for a reporting unit exceed its fair value, then the quantitative impairment test is failed and impaired goodwill is written down to its fair value with a charge to expense in the period the impairment is identified.

The fair value of each reporting unit for 2017 and 2016 was estimated using a combination of the income approach, which incorporates the use of the discounted cash flow method, and the market approach, which incorporates the use of earnings and revenue multiples based on market data.

We review intangible assets with definite lives subject to amortization whenever events or circumstances indicate that a carrying amount of an asset may not be recoverable. Recoverability of these assets is determined by comparing the carrying value of these assets to the estimated undiscounted future cash flows expected to be generated by these assets. These assets are impaired when their carrying value exceeds their fair value. Impaired intangible assets with definite lives subject to amortization are written down to their fair value with a charge to expense in the period the impairment is identified. Intangible assets with definite lives are amortized on a straight-line basis with estimated useful lives generally between 7 and 15 years. Events or circumstances that might require impairment testing include the loss of a significant client, the identification of other impaired assets within a reporting unit, loss of key personnel, the disposition of a significant portion of a reporting unit, significant decline in stock price or a significant adverse change in business climate or regulations.

Foreign Currencies

The functional currency of our foreign operations is generally their respective local currency. Assets and liabilities are translated at the exchange rates in effect at the balance sheet date, and revenues and expenses are translated at the average exchange rates during the period presented. The resulting translation adjustments are recorded as a component of accumulated other comprehensive loss in the stockholders’ equity section of our Consolidated Balance Sheets. Currency transaction gains or losses primarily arising from transactions in currencies other than the functional currency are included in office and general expenses. Foreign currency transactions resulted in pre-tax gains of $1.9, $2.1 and $2.0 in for the years ended December 31, 2017, 2016 and 2015, respectively.

We monitor the currencies of countries in which we operate in order to determine if the country should be considered a highly inflationary environment. A currency is determined to be highly inflationary when there is cumulative inflation of approximately 100% or more over a three-year period. If this occurs the functional currency of that country would be changed to our reporting currency, the U.S. Dollar, and foreign exchange gains or losses would be recognized on all monetary transactions, assets and liabilities in currencies other than the U.S. Dollar until the currency is no longer considered highly inflationary.

Income Taxes

The provision for income taxes includes U.S. federal, state, local and foreign taxes. Income taxes are accounted for under the liability method. Deferred tax assets and liabilities are recognized for the estimated future tax consequences of temporary differences between the financial statement carrying amounts and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the year in which the temporary differences are expected to be reversed. We evaluate the realizability of our deferred tax assets and establish a valuation allowance when it is “more likely than not” that all or a portion of the deferred tax assets will not be realized. We evaluate our tax positions using the “more likely than not” recognition threshold and then apply a measurement assessment to those positions that meet the recognition threshold. The factors used in assessing valuation allowances include all available evidence, such as past operating results, estimates of future taxable income and the feasibility of tax planning strategies. We have established tax reserves that we believe to be adequate in relation to the potential for additional assessments in each of the jurisdictions in which we are subject to taxation. We regularly assess the likelihood of additional tax assessments in those jurisdictions and adjust our reserves as additional information or events require.

In response to the enactment of the Tax Act, the SEC issued SAB 118 on December 22, 2017, which acknowledges that the information necessary to determine such income tax effects may not be sufficiently available, prepared or analyzed in reasonable detail to complete the accounting under U.S. GAAP. SAB 118 allows for the reporting of provisional amounts for those specific tax effects for which a reasonable estimate can be made, and for no amounts to be recorded where a reasonable estimate cannot be made. Any subsequent adjustments to reported amounts will be made over the measurement period, which begins in the reporting period that includes the Tax Act's enactment date and ends when an entity has obtained, prepared and analyzed the information that is needed in order to complete the accounting requirements under U.S. GAAP, not to exceed one year from the enactment date. We have reasonably estimated and recorded provisional amounts resulting from the enactment of the Tax Act. Refer to Note 7 to our Consolidated Financial Statements for further information.

Redeemable Noncontrolling Interests

Many of our acquisitions include provisions under which the noncontrolling equity owners can require us to purchase additional interests in a subsidiary at their discretion. Payments for these redeemable noncontrolling interests may be contingent on projected operating performance and satisfying other conditions specified in the related agreements. These payments are also subject to revision in accordance with the terms of the agreements. We record these redeemable noncontrolling interests in “mezzanine equity” in our Consolidated Balance Sheets. Each reporting period, redeemable noncontrolling interests are reported at their estimated redemption value, but not less than their initial fair value. Any adjustment to the redemption value above initial value prior to exercise will also impact retained earnings or additional paid-in capital (“APIC”), but will not impact net income. Adjustments as a result of currency translation will affect the redeemable noncontrolling interest balance, but do not impact retained earnings or additional paid-in capital.

Earnings Per Share (“EPS”)

Basic EPS available to IPG common stockholders equals net income available to IPG common stockholders divided by the weighted-average number of common shares outstanding for the applicable period. Diluted EPS equals net income available to IPG common stockholders divided by the weighted-average number of common shares outstanding, plus any additional common shares that would have been outstanding if potentially dilutive shares had been issued.

Diluted EPS reflect the potential dilution that would occur if certain potentially dilutive securities were exercised. The potential issuance of common stock is assumed to occur at the beginning of the year (or at the time of issuance of the potentially dilutive instrument, if later) and the incremental shares are included using the treasury stock method. The proceeds utilized in applying the treasury stock method consist of the amount, if any, to be paid upon exercise and, as it relates to stock-based compensation, the amount of compensation cost attributed to future service not yet recognized. These proceeds are then assumed to be used to purchase common stock at the average market price of our stock during the period. The incremental shares (difference between the shares assumed to be issued and the shares assumed to be purchased), to the extent they would have been dilutive, are included in the denominator of the diluted EPS calculation.

We may be required to calculate basic EPS using the two-class method as a result of our redeemable noncontrolling interests. To the extent that the redemption value increases and exceeds the then-current fair value of a redeemable noncontrolling interest, net income available to IPG common stockholders (used to calculate EPS) could be negatively impacted by that increase, subject to certain limitations. The partial or full recovery of any reductions to net income available to IPG common stockholders (used to calculate EPS) is limited to any cumulative prior-period reductions. For the years ended December 31, 2017, 2016 and 2015, there was no impact to EPS for adjustments related to our redeemable noncontrolling interests.

Pension and Postretirement Benefits

We have pension and postretirement benefit plans covering certain domestic and international employees. We use various actuarial methods and assumptions in determining our net pension and postretirement benefit costs and obligations, including the discount rate used to determine the present value of future benefits, expected long-term rate of return on plan assets and healthcare cost trend rates. The overfunded or underfunded status of our pension and postretirement benefit plans is recorded on our Consolidated Balance Sheet.

Stock-Based Compensation

Compensation costs related to share-based transactions, including employee stock options, are recognized in the Consolidated Financial Statements based on fair value. Stock-based compensation expense is generally recognized ratably over the requisite service period based on the estimated grant-date fair value, net of estimated forfeitures.

Treasury Stock

We account for repurchased common stock under the cost method and include such treasury stock as a component of our Consolidated Statements of Stockholders' Equity. Upon retirement, we reduce common stock for the par value of the shares being retired and the excess of the cost of the shares over par value as a reduction to APIC, to the extent there is APIC in the same class of stock, and any remaining amount to retained earnings. These retired shares remain authorized but unissued.

In October and November 2017, we retired 13.4 shares of our treasury stock, which resulted in a reduction in common stock of $1.3, treasury stock of $304.4 and APIC of $303.1. In October 2016, we retired 13.7 shares of our treasury stock, which resulted in a reduction in common stock of $1.4, treasury stock of $311.0 and APIC of $309.6. In October 2015, we retired 11.3 shares of our treasury stock, which resulted in a reduction in common stock of $1.2, treasury stock of $233.2 and APIC of $232.0. There was no effect on total stockholders' equity as a result of these retirements.

Debt and Credit Agreements (Notes)

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Debt Disclosure [Text Block]

Debt and Credit Arrangements

Long-Term Debt

A summary of the carrying amounts and fair values of our long-term debt is listed below.



	Effective Interest Rate		December 31,
			2017				2016
			Book Value		Fair Value ¹		Book Value		Fair Value ¹
2.25% Senior Notes due 2017	2.30	%	$	0.0	$	0.0	$	299.4	$	301.4
4.00% Senior Notes due 2022 (less unamortized discount and issuance costs of $1.3 and $1.1, respectively)	4.13	%	247.6		259.0		247.0		258.4
3.75% Senior Notes due 2023 (less unamortized discount and issuance costs of $0.8 and $2.1, respectively)	4.32	%	497.1		513.2		496.6		503.3
4.20% Senior Notes due 2024 (less unamortized discount and issuance costs of $0.7 and $2.6, respectively)	4.24	%	496.7		524.2		496.2		511.6
Other notes payable and capitalized leases			46.2		46.2		65.4		65.4
Total long-term debt			1,287.6				1,604.6
Less: current portion			2.0				323.9
Long-term debt, excluding current portion			$	1,285.6			$	1,280.7


1	See Note 10 for information on the fair value measurement of our long-term debt.

Annual maturities are scheduled as follows based on the book value as of December 31, 2017.



2018	$	2.0
2019	3.1
2020	1.0
2021	0.0
2022	247.6
Thereafter	1,033.9
Total long-term debt	$	1,287.6

For those debt securities that have a premium or discount at the time of issuance, we amortize the amount through interest expense based on the maturity date or the first date the holders may require us to repurchase the debt securities, if applicable. A premium would result in a decrease in interest expense, and a discount would result in an increase in interest expense in future periods. Additionally, we have debt issuance costs related to certain financing transactions which are also amortized through interest expense. As of December 31, 2017 and 2016, we had total unamortized debt issuance costs of $13.0 and $12.3, respectively.

Our debt securities include covenants that, among other things, limit our liens and the liens of certain of our consolidated subsidiaries, but do not require us to maintain any financial ratios or specified levels of net worth or liquidity.

Long-Term Debt Transactions

2.25% Senior Notes due 2017

In November 2017, we redeemed all $300.0 in aggregate principal amount of the 2.25% Senior Notes due 2017 (the "2.25% Notes"). Total cash paid to redeem the 2.25% Notes was $303.4, which included accrued and unpaid interest of $3.4.

Credit Agreements

We maintain a committed corporate credit facility, which has been amended and restated from time to time (the "Credit Agreement"). The Credit Agreement is a revolving facility, under which amounts borrowed by us or any of our subsidiaries designated under the Credit Agreement may be repaid and reborrowed, subject to an aggregate lending limit. On October 25, 2017, we amended and restated our committed credit agreement, originally dated as of July 18, 2008 (as amended and restated, the "Credit Agreement"), increasing the revolving commitments from $1,000.0 to $1,500.0, or the equivalent in other specified currencies, and extending the Credit Agreement's expiration to October 25, 2022.

We use our Credit Agreement to increase our financial flexibility, to provide letters of credit primarily to support obligations of our subsidiaries and to support our commercial paper program. The Company has the ability to increase the commitments under the Credit Agreement from time to time by an additional amount of up to $250.0, provided the Company receives commitments for such increases and satisfies certain other conditions. The aggregate available amount of letters of credit outstanding may decrease or increase, subject to a sublimit on letters of credit of $50.0, or the equivalent in other currencies. Our obligations under the Credit Agreement are unsecured. As of December 31, 2017 and 2016, there were no borrowings under the Credit Agreement; however, we had $8.4 and $4.9 of letters of credit under the Credit Agreement, which reduced our total availability to $1,491.6 and $995.1, respectively.

Under the Credit Agreement, we can elect to receive advances bearing interest based on either the base rate or the Eurocurrency rate (each as defined in the Credit Agreement) plus an applicable margin that is determined based on our credit ratings. As of December 31, 2017, the applicable margin was 0.10% for base rate advances and 1.10% for Eurocurrency rate advances. Letter of credit fees accrue on the average daily aggregate amount of letters of credit outstanding, at a rate equal to the applicable margin for Eurocurrency rate advances, and fronting fees accrue on the aggregate amount of letters of credit outstanding at an annual rate of 0.25%. We also pay a facility fee at an annual rate that is determined based on our credit ratings, which as of December 31, 2017, was 0.15% on the aggregate lending commitment under the Credit Agreement.

In addition to other and customary covenants, the Credit Agreement requires that we maintain the financial covenants listed below as of the end of each fiscal quarter for the period of four fiscal quarters then ended. We were in compliance with all of our covenants in the Credit Agreement as of December 31, 2017.



Interest coverage ratio (not less than): ¹		5.00x
Leverage ratio (not greater than): ²		3.50x


1	The interest coverage ratio is defined as EBITDA, as defined in the Credit Agreement, to net interest expense for the four quarters then ended.

The leverage ratio is defined as debt as of the last day of such fiscal quarter to EBITDA, as defined in the Credit Agreement, for the four quarters then ended. The leverage ratio may be changed to not more than 4.00 to 1 at our election for four consecutive fiscal quarters, beginning with the fiscal quarter in which there is an occurrence of one or more acquisitions with an aggregate purchase price of at least $200.0.

We also have uncommitted lines of credit with various banks which permit borrowings at variable interest rates and which are primarily used to fund working capital needs. We have guaranteed the repayment of some of these borrowings made by certain subsidiaries. If we lose access to these credit lines, we would have to provide funding directly to some of our operations. As of December 31, 2017 and 2016, the Company had uncommitted lines of credit in an aggregate amount of $926.2 and $856.6, under which we had outstanding borrowings of $84.9 and $85.7 classified as short-term borrowings on our Consolidated Balance Sheets, respectively. The average amounts outstanding during 2017 and 2016 were $223.8 and $216.0, respectively, with weighted-average interest rates of approximately 2.9% for both periods.

Commercial Paper

In June 2017, the Company established a commercial paper program under which the Company was authorized to issue unsecured commercial paper up to a maximum aggregate amount outstanding at any time of $1,000.0, which was increased to $1,500.0 on October 25, 2017. Borrowings under the program are supported by the Credit Agreement described above. Proceeds of the commercial paper are used for working capital and general corporate purposes, including the repayment of maturing indebtedness and other short-term liquidity needs. The maturities of the commercial paper vary but may not exceed 397 days from the date of issue. As of December 31, 2017, there was no commercial paper outstanding. From the date the program was first utilized through December 31, 2017, the average amount outstanding under the program was $477.4, with a weighted-average interest rate of 1.5% and a weighted-average maturity of seventeen days.

Cash Pooling

We aggregate our domestic cash position on a daily basis. Outside the United States, we use cash pooling arrangements with banks to help manage our liquidity requirements. In these pooling arrangements, several IPG agencies agree with a single bank that the cash balances of any of the agencies with the bank will be subject to a full right of set-off against amounts other agencies owe the bank, and the bank provides for overdrafts as long as the net balance for all agencies does not exceed an agreed-upon level. Typically, each agency pays interest on outstanding overdrafts and receives interest on cash balances. Our Consolidated Balance Sheets reflect cash, net of bank overdrafts, under all of our pooling arrangements, and as of December 31, 2017 and 2016 the amounts netted were $1,412.0 and $1,300.6, respectively.

Acquisitions (Notes)

12 Months Ended

Dec. 31, 2017

Business Combinations [Abstract]

Acquisitions

We continue to evaluate strategic opportunities to expand our industry expertise, strengthen our position in high-growth and key strategic geographical markets and industry sectors, advance technological capabilities and improve operational efficiency through both acquisitions and increased ownership interests in current investments. Our acquisitions typically provide for an initial payment at the time of closing and additional contingent purchase price payments based on the future performance of the acquired entity. We have entered into agreements that may require us to purchase additional equity interests in certain consolidated and unconsolidated subsidiaries. The amounts at which we record these transactions in our financial statements are based on estimates of the future financial performance of the acquired entity, the timing of the exercise of these rights, changes in foreign currency exchange rates and other factors.

During 2017, we completed ten acquisitions, eight of which were included in the Integrated Agency Networks ("IAN") operating segment, and two of which were included in the Constituency Management Group ("CMG") operating segment. These acquisitions included a digital marketing agency based in the U.S., a data science and business intelligence firm based in the U.S. with operations in China, an advertising and consulting company based in Indonesia, a strategic communications agency based in the U.K., an independent creative agency based in the U.K., a retail branding and design firm based in the U.S., a content creation and marketing agency based in the Netherlands, an independent media agency and digital consultancy based in Finland, and an integrated marketing communications agency based in Canada. During 2017, we recorded approximately $62.0 of goodwill and intangible assets related to our acquisitions.

During 2016, we completed ten acquisitions, three of which were included in the IAN operating segment, and seven of which were included in the CMG operating segment. The most significant acquisitions included a product and service design consultancy based in the U.S., an integrated healthcare marketing communications agency based in the U.S., a content creation and digital agency with offices in the U.S. and the U.K., a mobile consultancy and application development agency based in the U.K., a full-service public relations and digital agency based in China, a search engine optimization and digital content marketing agency based in the U.K., and a mobile focused digital agency based in the U.K. During 2016, we recorded approximately $149.0 of goodwill and intangible assets related to these acquisitions.

During 2015, we completed five acquisitions, four of which were included in the IAN operating segment, and one of which was included in the CMG operating segment. The most significant acquisitions included a full-service digital agency in the U.K., a group of creative marketing agencies based in Russia, and a media planning and buying agency with significant digital capabilities in Canada. During 2015, we recorded approximately $61.0 of goodwill and intangible assets related to these acquisitions.

The results of operations of our acquired companies were included in our consolidated results from the closing date of each acquisition. We did not make any payments in stock related to our acquisitions in 2017, 2016 or 2015.

Details of cash paid for current and prior years' acquisitions are listed below.



	Years ended December 31,
	2017			2016			2015
Cost of investment: current-year acquisitions	$	36.8		$	65.7		$	37.8
Cost of investment: prior-year acquisitions	54.6			40.7			53.1
Less: net cash acquired	(7.1		)	(13.6		)	(9.2		)
Total cost of investment	84.3			92.8			81.7
Operating payments¹	47.1			19.1			18.4
Total cash paid for acquisitions ²	$	131.4		$	111.9		$	100.1

Represents cash payments for amounts that have been recognized in operating expenses since the date of acquisition either relating to adjustments to estimates in excess of the initial value of contingent payments recorded or were contingent upon the future employment of the former owners of the acquired companies. Amounts are reflected in the operating section of the Consolidated Statements of Cash Flows.

Of the total cash paid for acquisitions, $30.6, $52.0 and $28.6 for the years ended December 31, 2017, 2016 and 2015, respectively, are classified under the investing section of the Consolidated Statements of Cash Flows as acquisitions, net of cash acquired. These amounts relate to initial payments for new transactions. Of the total cash paid for acquisitions, $53.7, $40.8 and $53.1 for the years ended December 31, 2017, 2016 and 2015, respectively, are classified under the financing section of the Consolidated Statements of Cash Flows as acquisition-related payments. These amounts relate to deferred payments and increases in our ownership interest for prior acquisitions.

For companies acquired, we estimate the fair values of the assets and liabilities based on 100% of the business for consolidation. The purchase price in excess of the estimated fair value of the tangible net assets acquired is allocated to identifiable intangible assets and then to goodwill. Due to the characteristics of advertising, specialized marketing and communication services companies, our acquisitions typically do not have significant amounts of tangible assets since the principal assets we acquire are client relationships and talent. As a result, a substantial portion of the purchase price is primarily allocated to customer lists, trade names and goodwill.

For acquisitions we record deferred payment and redeemable noncontrolling interest amounts on our Consolidated Balance Sheets based on their acquisition-date fair value. Deferred payments are recorded on a discounted basis and adjusted quarterly, if necessary, through operating income or net interest expense, depending on the nature of the arrangement, for both changes in estimate and accretion between the acquisition date and the final payment date. See Note 13 for further information on contingent acquisition obligations. Redeemable noncontrolling interests are adjusted quarterly to their estimated redemption value, but not less than their initial fair value. Any adjustments to the redemption value impact retained earnings, except for foreign currency translation adjustments. The following table presents changes in our redeemable noncontrolling interests.



	Years ended December 31,
	2017			2016			2015
Balance at beginning of period	$	252.8		$	251.9		$	257.4
Change in related noncontrolling interests balance	(2.8		)	4.9			0.8
Changes in redemption value of redeemable noncontrolling interests:
Additions	7.7			6.8			16.5
Redemptions and other	(18.5		)	(14.8		)	(25.1		)
Redemption value adjustments	12.9			4.0			2.3
Balance at end of period	$	252.1		$	252.8		$	251.9

For all acquisitions, if a portion of the deferred payments and purchases of additional interests after the effective date of purchase are contingent upon employment terms, then that amount is accounted for separately from the business combination and recognized as compensation expense over the required earn-out period. Payments deemed as compensation are excluded from the fair value purchase price allocation to tangible net assets and intangible assets acquired.

Supplementary Data (Notes)

12 Months Ended

Dec. 31, 2017

Supplementary Data [Abstract]

Supplementary Data

Valuation and Qualifying Accounts – Allowance for Uncollectible Accounts Receivable



	Years ended December 31,
	2017			2016			2015
Balance at beginning of period	$	55.7		$	54.2		$	59.5
Charges to costs and expenses	9.5			16.7			11.4
Deductions:
Dispositions	(1.0		)	(2.5		)	(2.8		)
Uncollectible accounts written off	(25.5		)	(9.4		)	(9.8		)
Foreign currency translation adjustments	4.0			(3.3		)	(4.1		)
Balance at end of period	$	42.7		$	55.7		$	54.2

Property and Equipment



	December 31,
	2017			2016
Furniture and equipment	$	634.8		$	604.2
Leasehold improvements	641.5			599.8
Internal-use computer software	331.3			306.5
Land and buildings	79.0			73.1
Gross property and equipment	1,686.6			1,583.6
Less: accumulated depreciation	(1,036.2		)	(961.6		)
Total property and equipment, net	$	650.4		$	622.0

Total depreciation and amortization expense for property and equipment for the years ended December 31, 2017, 2016 and 2015 was $135.9, $138.3 and $130.9, respectively.

Accrued Liabilities

The following table presents the components of accrued liabilities.



	December 31,
	2017		2016
Salaries, benefits and related expenses	$	441.7	$	499.0
Office and related expenses	53.2		46.7
Acquisition obligations	42.0		77.5
Interest	16.4		17.3
Other	121.4		153.5
Total accrued liabilities	$	674.7	$	794.0

Other Expense, net

Results of operations include certain items that are not directly associated with our revenue-producing operations.



	Years ended December 31,
	2017			2016			2015
Net losses on sales of businesses	$	(24.1	)	$	(41.4	)	$	(50.0	)
Other	(2.1		)	1.1			0.4
Total other expense, net	$	(26.2	)	$	(40.3	)	$	(49.6	)

Net losses on sales of businesses – During 2017, the amounts recognized were primarily related to sales of businesses and the classification of certain assets and liabilities, consisting primarily of cash, accounts receivable and accounts payable, as held for sale within our IAN operating segment. The businesses held for sale as of year end primarily represent unprofitable, non-strategic agencies which are expected to be sold within the next twelve months. During 2016, the amounts recognized were related to sales of businesses and the classification of certain assets and liabilities, consisting primarily of accounts receivable and accounts payable, as held for sale within both our IAN and CMG operating segments. During 2015, the amounts recognized were related to sales of businesses within both our IAN and CMG operating segments and the classification of certain assets and liabilities, consisting primarily of accounts receivable and accounts payable, as held for sale within our IAN operating segment.

Share Repurchase Program

In February 2017, our Board of Directors (the "Board") authorized a new share repurchase program to repurchase from time to time up to $300.0, excluding fees, of our common stock (the "2017 Share Repurchase Program"), which was in addition to the remaining amount available to be repurchased from the $300.0 authorization made by the Board in February 2016 (the "2016 Share Repurchase Program").

We may effect such repurchases through open market purchases, trading plans established in accordance with U.S. Securities and Exchange Commission ("SEC") rules, derivative transactions or other means. We expect to continue to repurchase our common stock in future periods, although the timing and amount of the repurchases will depend on market conditions and other funding requirements.

The following table presents our share repurchase activity under our share repurchase programs.



	Years ended December 31,
	2017		2016		2015
Number of shares repurchased	13.7		13.3		13.6
Aggregate cost, including fees	$	300.1	$	303.3	$	285.2
Average price per share, including fees	$	21.97	$	22.76	$	20.97

We fully utilized the 2016 Share Repurchase Program in the third quarter of 2017. As of December 31, 2017, $155.5 remained available for repurchase under the 2017 Share Repurchase Program. The 2017 Share Repurchase Program has no expiration date.

Supplemental Cash Flow Information



	Years ended December 31,
	2017		2016		2015
Cash paid for interest	$	82.3	$	78.8	$	74.5
Cash paid for income taxes, net of refunds ¹	228.4		244.1		231.9


1	Refunds of $31.9, $26.6 and $13.0 were received for the years ended December 31, 2017, 2016 and 2015, respectively.

Intangible Assets (Notes)

12 Months Ended

Dec. 31, 2017

Goodwill and Intangible Assets [Abstract]

Goodwill and Intangible Assets Disclosure [Text Block]

Intangible Assets

Goodwill

Goodwill is the excess purchase price remaining from an acquisition after an allocation of purchase price has been made to identifiable assets acquired and liabilities assumed based on estimated fair values. The changes in the carrying value of goodwill for our segments, IAN and CMG, for the years ended December 31, 2017 and 2016 are listed below.



	IAN			CMG			Total ¹
Balance as of December 31, 2015	$	3,051.4		$	557.1		$	3,608.5
Acquisitions	32.7			89.3			122.0
Foreign currency and other	(40.3		)	(15.8		)	(56.1		)
Balance as of December 31, 2016	$	3,043.8		$	630.6		$	3,674.4
Acquisitions	39.6			15.5			55.1
Foreign currency and other	78.4			12.5			90.9
Balance as of December 31, 2017	$	3,161.8		$	658.6		$	3,820.4


1	For all periods presented, no goodwill impairment charge has been recorded.

See Note 1 for information regarding our annual impairment methodology.

Other Intangible Assets

Other intangible assets are comprised of both assets with indefinite lives not subject to amortization and assets with definite lives subject to amortization. Other intangible assets primarily consist of customer lists and trade names, which have definitive lives and are subject to amortization on a straight-line basis with estimated useful lives generally between 7 and 15 years. Amortization expense for other intangible assets for the years ended December 31, 2017, 2016 and 2015 was $21.2, $21.9 and $26.1, respectively. There were no material impairment charges on other intangibles for the years ended December 31, 2017, 2016 and 2015. During 2017 and 2016, we recorded approximately $7.0 and $29.0 of intangible assets related to our acquisitions in the respective year.

The following table provides a summary of other intangible assets, which are included in other assets on our Consolidated Balance Sheets.



	December 31,
	2017							2016
	Gross Amount		Accumulated Amortization			Net Amount		Gross Amount		Accumulated Amortization			Net Amount
Customer lists	$	267.3	$	(172.2	)	$	95.1	$	252.4	$	(151.4	)	$	101.0
Trade names	68.8		(33.8		)	35.0		65.5		(28.9		)	36.6
Other	14.4		(3.8		)	10.6		14.3		(3.8		)	10.5
Total	$	350.5	$	(209.8	)	$	140.7	$	332.2	$	(184.1	)	$	148.1

The estimated annual amortization expense for other intangible assets for the next five years as of December 31, 2017 is listed below.



	2018		2019		2020		2021		2022
Estimated amortization expense	$	23.3	$	22.1	$	20.4	$	19.3	$	16.4

- Definition

The entire disclosure for the aggregate amount of goodwill and a description of intangible assets, which may include (a) for amortizable intangible assets (also referred to as finite-lived intangible assets), the carrying amount, the amount of any significant residual value, and the weighted-average amortization period, (b) for intangible assets not subject to amortization (also referred to as indefinite-lived intangible assets), the carrying amount, and (c) the amount of research and development assets acquired and written off in the period, including the line item in the income statement in which the amounts written off are aggregated, if not readily apparent from the income statement. Also discloses (a) for amortizable intangibles assets in total and by major class, the gross carrying amount and accumulated amortization, the total amortization expense for the period, and the estimated aggregate amortization expense for each of the five succeeding fiscal years, (b) for intangible assets not subject to amortization the carrying amount in total and by major class, and (c) for goodwill, in total and for each reportable segment, the changes in the carrying amount of goodwill during the period (including the aggregate amount of goodwill acquired, the aggregate amount of impairment losses recognized, and the amount of goodwill included in the gain (loss) on disposal of a reporting unit). If any part of goodwill has not been allocated to a reportable segment, discloses the unallocated amount and the reasons for not allocating. For each impairment loss recognized related to an intangible asset (excluding goodwill), discloses: (a) a description of the impaired intangible asset and the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method for determining fair value, (c) the caption in the income statement or the statement of activities in which the impairment loss is aggregated, and (d) the segment in which the impaired intangible asset is reported. For each goodwill impairment loss recognized, discloses: (a) a description of the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method of determining the fair value of the associated reporting unit, and (c) if a recognized impairment loss is an estimate not finalized and the reasons why the estimate is not final. May also disclose the nature and amount of any significant adjustments made to a previous estimate of an impairment loss.

+ References + Details

Income Taxes (Notes)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income Tax Disclosure [Text Block]

Income Taxes

Public Law 115-97, commonly referred to as the Tax Cuts and Jobs Act (the "Tax Act"), was enacted on December 22, 2017. The Tax Act legislated many new tax provisions which have impacted our operations, including the reduction of the U.S. federal income tax rate from 35.0% to 21.0%, effective in 2018, a current tax on the deemed repatriation of unremitted foreign earnings and a U.S tax exemption for future distributions of certain foreign earnings.

U.S. GAAP requires the income tax accounting effect of a change in tax law, including the effects on current and deferred income taxes, to be reflected in the period in which such law is enacted. The SEC issued Staff Accounting Bulletin No. 118 ("SAB 118") on December 22, 2017, which acknowledges that the information necessary to determine such income tax effects may not be sufficiently available, prepared or analyzed in reasonable detail to complete the accounting under U.S. GAAP. SAB 118 allows for the reporting of provisional amounts for those specific tax effects for which a reasonable estimate can be made, and for no amounts to be recorded where a reasonable estimate cannot be made. Any subsequent adjustments to reported amounts will be made over the measurement period, which begins in the reporting period that includes the Tax Act's enactment date and ends when an entity has obtained, prepared and analyzed the information that is needed in order to complete the accounting requirements under U.S. GAAP, not to exceed one year from the enactment date.

We have reasonably estimated the tax effect of re-measuring our deferred tax balances and reserves at year end to reflect the tax effect of the reversal of such deferred tax balances in future periods during which the U.S. federal income tax rate will be 21.0%. We have recorded a decrease related to deferred tax assets and deferred tax liabilities, with a corresponding provisional net benefit to our deferred income taxes of $104.7. The Tax Act’s various changes to the treatment of fixed assets and deferred compensation are sufficiently complex to conclude that an adjustment may be necessary.

The Tax Act also imposes a tax on certain unremitted foreign earnings at various tax rates. We have reasonably estimated the tax effect of this deemed repatriation of unremitted foreign earnings and have recorded tax expense of $62.3 as a provisional amount due to the fact that necessary information could not be attained, prepared or analyzed on a timely basis to be able to complete the calculations. The complexity of the rules and the comprehensive data requirements will likely result in some adjustment to the provisional amount. The Company expects to pay this amount over the next eight years, as allowed by the Tax Act.

Additionally, the Tax Act imposes a new tax on certain foreign earnings generated in 2018 and forward. We are continuing to evaluate these global intangible low-taxed income ("GILTI") tax rules, which are extremely complex. U.S. GAAP allows us to choose between an accounting policy which treats the U.S. tax under GILTI provisions as either a current expense, as incurred, or as a component of the Company’s measurement of deferred taxes. We are not able to reasonably estimate the effect of the GILTI rules due to the significant complexity of the rules and the fact that the information necessary could not be attained, prepared or analyzed on a timely basis. Therefore, we have not made any adjustment related to the potential GILTI tax and have not made a policy decision regarding whether to record deferred taxes thereon.

Finally, as per interpretive guidance issued by the U.S. Treasury on February 13, 2018, a tax benefit of $31.2, which was recorded during the third quarter of 2017, was reversed during the fourth quarter of 2017 due to the enactment of the Tax Act.

The components of income before income taxes are listed below.



	Years ended December 31,
	2017		2016		2015
Domestic	$	528.2	$	504.7	$	461.0
Foreign	347.8		325.5		301.2
Total	$	876.0	$	830.2	$	762.2

The provision for income taxes is listed below.



	Years ended December 31,
	2017			2016			2015
U.S. federal income taxes (including foreign withholding taxes):
Current	$	154.1		$	54.3		$	117.8
Deferred	(32.2		)	36.6			46.9
	121.9			90.9			164.7
State and local income taxes:
Current	18.8			8.2			15.1
Deferred	20.4			(1.5		)	13.0
	39.2			6.7			28.1
Foreign income taxes:
Current	107.9			89.8			100.4
Deferred	12.9			10.6			(10.4		)
	120.8			100.4			90.0
Total	$	281.9		$	198.0		$	282.8

A reconciliation of the effective income tax rate as reflected in our Consolidated Statements of Operations to the U.S. federal statutory income tax rate is listed below.



	Years ended December 31,
	2017			2016			2015
U.S. federal statutory income tax rate	35.0		%	35.0		%	35.0		%

Income tax provision at U.S. federal statutory rate	$	306.6		$	290.6		$	266.8
State and local income taxes, net of U.S. federal income tax benefit	23.5			4.3			18.3
Impact of foreign operations, including withholding taxes	(6.7		)	(23.9		)	14.7
Change in net valuation allowance ¹	1.4			(13.4		)	(20.6		)
Divestitures	1.1			9.7			11.9
U.S. federal tax credits	(1.7		)	(44.6		)	0.0
Stock compensation	(15.3		)	(9.0		)	0.0
Increase/(decrease) in unrecognized tax benefits	7.0			(22.2		)	(6.5		)
Net impact of the Tax Act	(36.0		)	0.0			0.0
Statutory tax rate changes	0.0			11.4			1.4
Other	2.0			(4.9		)	(3.2		)
Provision for income taxes	$	281.9		$	198.0		$	282.8

Effective income tax rate on operations	32.2		%	23.8		%	37.1		%


1	Reflects changes in valuation allowances that impacted the effective income tax rate for each year presented.

In 2017, our effective income tax rate of 32.2% was positively impacted by a net benefit of $36.0 as a result of the Tax Act, the primary impacts of which are discussed above, and excess tax benefits on employee share-based payments, partially offset by losses in certain foreign jurisdictions where we receive no tax benefit due to 100% valuation allowances.

In 2016, our effective income tax rate of 23.8% was positively impacted by a benefit of $44.6 related to refunds to be claimed on future amended U.S. federal returns for tax years 2014 and 2015 primarily related to foreign tax credits and, to a lesser extent, research and development credits based on the conclusion of multi-year studies; the settlement of 2011 and 2012 income tax audits, which included the recognition of certain previously unrecognized tax benefits of $23.4; the reversal of valuation allowances of $12.2 as a consequence of the disposition of certain businesses in Continental Europe; excess tax benefits on employee share-based payments; and various changes in state income tax laws as well as the recognition of previously unrecognized state tax benefits as a result of a lapse in statute of limitations. The positive impacts to our tax rates were partially offset by a revaluation of deferred tax assets as a result of a statutory tax rate change in Continental Europe, losses in certain foreign jurisdictions where we receive no tax benefit due to 100% valuation allowances and by losses on sales of businesses for which we did not receive a full tax benefit.

In 2015, our effective income tax rate of 37.1% was negatively impacted primarily by losses in certain foreign jurisdictions where we receive no tax benefit due to 100% valuation allowances and from the losses on sales of businesses for which we did not receive a full tax benefit. The negative impacts to our tax rates were partially offset by the recognition of previously unrecognized tax benefits as a result of the reversal of valuation allowances in Continental Europe and the settlement of a 2010 income tax audit.

The components of deferred tax assets and liabilities are listed below.



	December 31,
	2017			2016
Postretirement/post-employment benefits	$	19.5		$	23.1
Deferred compensation	91.7			192.4
Pension costs	27.6			36.6
Basis differences in fixed assets	(52.0		)	(80.2		)
Rent	27.5			41.7
Interest	45.8			58.9
Accruals and reserves	18.4			17.2
Allowance for doubtful accounts	10.2			13.3
Basis differences in intangible assets	(281.3		)	(405.0		)
Investments in equity securities	(3.3		)	(6.3		)
Tax loss/tax credit carry forwards	357.9			354.6
Prepaid expenses	(1.7		)	(2.9		)
Deferred revenue	(38.2		)	(32.0		)
Other	44.7			44.3
Total deferred tax assets, net	266.8			255.7
Valuation allowance	(243.3		)	(255.6		)
Net deferred tax assets	$	23.5		$	0.1

As a result of the Tax Act, we have re-measured our deferred tax assets and liabilities to reflect the tax effect of the reversal of such balances in future periods during which the U.S. federal income tax rate will be 21.0%, resulting in a provisional net benefit to our deferred income taxes of $104.7. However, the Tax Act’s various changes to the treatment of fixed assets and deferred compensation are sufficiently complex to conclude that an adjustment may be necessary.

We evaluate the realizability of our deferred tax assets on a quarterly basis. The realization of our deferred tax assets is primarily dependent on future earnings. The amount of the deferred tax assets considered realizable could be reduced or increased in the near future if estimates of future taxable income are lower or greater than anticipated. A valuation allowance is established when it is “more likely than not” that all or a portion of deferred tax assets will not be realized. In circumstances where there is negative evidence, establishment of a valuation allowance is considered. The factors used in assessing valuation allowances include all available evidence, such as past operating results, estimates of future taxable income and the feasibility of tax planning strategies. We believe that cumulative losses in the most recent three-year period represent significant negative evidence, and as a result, we determined that certain of our deferred tax assets required the establishment of a valuation allowance. The deferred tax assets for which an allowance was recognized relate primarily to state and foreign tax loss carryforwards.

The change in the valuation allowance is listed below.



	Years ended December 31,
	2017			2016			2015
Balance at beginning of period	$	255.6		$	275.1		$	332.2
Reversed to costs and expenses	(4.6		)	(15.4		)	(20.8		)
(Reversed) charged to gross tax assets and other accounts ¹	(27.0		)	9.5			(9.2		)
Foreign currency translation	19.3			(13.6		)	(27.1		)
Balance at end of period	$	243.3		$	255.6		$	275.1


1	Primarily represents changes to the valuation allowance related to the change of a corresponding deferred tax asset.

In 2017, 2016, and 2015, amounts reversed to costs and expenses primarily related to decreases in valuation allowances in Continental Europe for existing deferred tax assets.

As of December 31, 2017, there were $1,186.8 of loss carryforwards. These loss carryforwards were all non-U.S. tax loss carryforwards, of which $656.6 have unlimited carryforward periods and $530.2 have expiration periods from 2018 to 2037. As of December 31, 2017, the Company also had $45.0 in deferred tax assets for state net operating loss carryforwards and tax credit carryforwards, which will expire between 2018 and 2037.

As of December 31, 2017 and 2016, we had $2,774.8 and $2,622.4, respectively, of undistributed earnings attributable to foreign subsidiaries. The Company has historically asserted that its unremitted foreign earnings are permanently reinvested, and therefore, has not recorded deferred taxes on such amounts. The Tax Act provides a U.S. tax exemption for dividends of certain foreign earnings. The Tax Act may provide additional flexibility in the Company’s tax-efficient access to global cash, but is expected to have limited impact to net domestic liquidity. The Company is still evaluating whether to continue its indefinite reinvestment assertion, in light of the Tax Act. Any change to the assertion will be accounted for as part of the change in tax law, as permitted by SAB 118.

The table below summarizes the activity related to our unrecognized tax benefits.



	Years ended December 31,
	2017			2016			2015
Balance at beginning of period	$	246.7		$	226.9		$	238.0
Increases as a result of tax positions taken during a prior year	6.3			65.0			5.2
Decreases as a result of tax positions taken during a prior year	(8.1		)	(47.5		)	(19.7		)
Settlements with taxing authorities	(0.8		)	(4.6		)	(4.1		)
Lapse of statutes of limitation	(3.3		)	(11.8		)	(3.8		)
Increases as a result of tax positions taken during the current year	31.1			18.7			11.3
Balance at end of period	$	271.9		$	246.7		$	226.9

Included in the total amount of unrecognized tax benefits of $271.9 as of December 31, 2017, is $249.2 of tax benefits that, if recognized, would impact the effective income tax rate. The total amount of accrued interest and penalties as of December 31, 2017 and 2016 is $27.9 and $20.9, respectively, of which a detriment of $7.0 and $0.7 is included in our 2017 and 2016 Consolidated Statements of Operations, respectively. In accordance with our accounting policy, interest and penalties accrued on unrecognized tax benefits are classified as income taxes in our Consolidated Statements of Operations.

We have various tax years under examination by tax authorities in the U.S., in various countries, and in various states, such as New York, in which we have significant business operations. It is not yet known whether these examinations will, in the aggregate, result in our paying additional taxes. We believe our tax reserves are adequate in relation to the potential for additional assessments in each of the jurisdictions in which we are subject to taxation. We regularly assess the likelihood of additional tax assessments in those jurisdictions and, if necessary, adjust our reserves as additional information or events require.

With respect to all tax years open to examination by U.S. federal, various state and local, and non-U.S. tax authorities, we currently anticipate that total unrecognized tax benefits will decrease by an amount between $28.0 and $38.0 in the next twelve months, a portion of which will affect our effective income tax rate, primarily as a result of the settlement of tax examinations and the lapsing of statutes of limitations. This net decrease is related to various items of income and expense, primarily transfer pricing adjustments.

We are effectively settled with respect to U.S. federal income tax audits through 2012, with the exception of 2009. With limited exceptions, we are no longer subject to state and local income tax audits for years prior to 2007 or non-U.S. income tax audits for years prior to 2006.

Accumulated Other Comprehensive Loss, Net of Tax (Notes)

12 Months Ended

Dec. 31, 2017

Accumulated Other Comprehensive Loss [Abstract]

Comprehensive Income (Loss) Note

Accumulated Other Comprehensive Loss, Net of Tax

The following table presents the changes in accumulated other comprehensive loss, net of tax, by component.



	Foreign Currency Translation Adjustments			Available-for-Sale Securities			Derivative Instruments			Defined Benefit Pension and Other Postretirement Plans			Total
Balance as of December 31, 2015	$	(665.6	)	$	1.3		$	(9.6	)	$	(171.7	)	$	(845.6	)
Other comprehensive (loss) income before reclassifications	(54.8		)	0.5			0.0			(70.7		)	(125.0		)
Amount reclassified from accumulated other comprehensive loss, net of tax	3.7			(1.2		)	1.2			4.4			8.1
Balance as of December 31, 2016	$	(716.7	)	$	0.6		$	(8.4	)	$	(238.0	)	$	(962.5	)
Other comprehensive income (loss) before reclassifications	130.7			0.0			0.0			(9.7		)	121.0
Amount reclassified from accumulated other comprehensive loss, net of tax	1.1			(0.6		)	1.6			12.0			14.1
Balance as of December 31, 2017	$	(584.9	)	$	0.0		$	(6.8	)	$	(235.7	)	$	(827.4	)

Amounts reclassified from accumulated other comprehensive loss, net of tax, for the years ended December 31, 2017, 2016 and 2015 are as follows:



	Years ended December 31,									Affected Line Item in the Consolidated Statements of Operations
	2017			2016			2015
Foreign currency translation adjustments ¹	$	1.1		$	3.7		$	23.3		Other expense, net
Gains on available-for-sale securities	(0.7		)	(1.3		)	0.0			Other expense, net
Losses on derivative instruments	2.1			2.0			2.0			Interest expense
Amortization of defined benefit pension and postretirement plans items	13.7			5.8			10.4			Other expense, net
Tax effect	(2.1		)	(2.1		)	(4.2		)	Provision for income taxes
Total amount reclassified from accumulated other comprehensive loss, net of tax	$	14.1		$	8.1		$	31.5


1	These foreign currency translation adjustments are primarily a result of the sales of businesses.

Incentive Compensation Plans (Notes)

12 Months Ended

Dec. 31, 2017

Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]

Incentive Compensation Plans

2014 Performance Incentive Plan

We issue stock-based compensation and cash awards to our employees under a plan established by the Compensation and Leadership Talent Committee of the Board of Directors (the “Compensation Committee”) and approved by our shareholders. In May 2014, our shareholders approved the 2014 Performance Incentive Plan (the “2014 PIP”), replacing previous incentive plans. The number of shares of common stock initially available for grants of all equity awards under the 2014 PIP is 28.8. Pursuant to the terms of the 2014 PIP, the number of shares that may be awarded to any one participant for each type of award is limited to 2.0. The vesting period of awards granted is generally commensurate with the requisite service period. We generally issue new shares to satisfy the exercise of stock options or the distribution of other stock-based awards.

Additionally, under the 2014 PIP, we have the ability to issue performance cash awards. Performance cash awards are granted to certain employees who otherwise would have been eligible to receive performance-based stock awards. These awards have a service period vesting condition and a performance vesting condition. The amount of the performance cash award received by an employee with a performance vesting condition can range from 0% to 300% of the target amount of the original grant value, except for Executive Officers of IPG, with a range of 0% to 200%. Performance cash awards generally vest in three years. The Compensation Committee may grant performance cash awards to any eligible employee; however, no employee can receive more than $10.0 during a performance period.

The amounts of stock-based compensation expense as reflected in salaries and related expenses in our Consolidated Statements of Operations, and the related tax benefit, are listed below.



	Years ended December 31,
	2017		2016		2015
Stock options	$	0.0	$	0.2	$	1.0
Stock-settled awards	20.5		16.0		11.6
Cash-settled awards	1.0		0.9		0.7
Performance-based awards	61.5		69.4		57.7
Employee stock purchase plan	1.0		0.7		0.7
Other ¹	0.5		0.8		0.9
Stock-based compensation expense	$	84.5	$	88.0	$	72.6
Tax benefit	$	30.4	$	32.1	$	26.3


1	Represents charges recorded for severance expense related to stock-based compensation awards.

Stock Options

Stock options are granted with the exercise price equal to the fair market value of our common stock on the grant date. We use the Black-Scholes option-pricing model to estimate the fair value of options granted, which requires the input of subjective assumptions including the option’s expected term and the price volatility of the underlying stock. They are generally first exercisable between two and four years from the grant date and expire ten years from the grant date (or earlier in the case of certain terminations of employment). There were no stock options granted during the years ended December 31, 2017, 2016 and 2015. As of December 31, 2017, all stock options granted were fully vested and exercisable.

The following table summarizes our stock option activity during 2017.



	Options		Weighted- Average Exercise Price (per option)		Weighted- Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Stock options outstanding as of January 1, 2017	4.8		$	9.83
Exercised	(1.1	)	11.15
Stock options outstanding as of December 31, 2017	3.7		$	9.44	2.6	$	39.2

There were 1.1, 1.2 and 1.4 stock options exercised in 2017, 2016 and 2015, respectively. The total intrinsic value of stock options exercised during 2017, 2016 and 2015 was $15.1, $15.2 and $16.1, respectively. The cash received from the stock options exercised in 2017, 2016 and 2015 was $20.0, $18.2 and $20.4, respectively.

Stock-Based Compensation

We grant other stock-based compensation awards such as stock-settled awards, cash-settled awards and performance-based awards (settled in cash or shares) to certain key employees. The number of shares or units received by an employee for performance-based awards depends on Company performance against specific performance targets and could range from 0% to 300% of the target amount of shares originally granted, except for Executive Officers of IPG, with a range of 0% to 200%. Incentive awards are subject to certain restrictions and vesting requirements as determined by the Compensation Committee. The fair value of the shares on the grant date is amortized over the vesting period, which is generally three years. Upon completion of the vesting period for cash-settled awards, the grantee is entitled to receive a payment in cash based on the fair market value of the corresponding number of shares of common stock. No monetary consideration is paid by a recipient for any incentive award. The fair value of cash-settled awards is adjusted each quarter based on our share price. The holders of stock-settled awards have absolute ownership interest in the underlying shares of common stock prior to vesting, which includes the right to vote and receive dividends. Dividends declared on common stock are accrued during the vesting period and paid when the award vests. The holders of performance-based awards have no ownership interest in the underlying shares of common stock until the awards vest and the shares of common stock are issued.

Stock-based compensation awards expected to be settled in cash have been classified as liabilities in our Consolidated Balance Sheets as of December 31, 2017 and 2016.



	Years ended December 31,
	2017		2016		2015
Stock-Settled Awards:
Awards granted	0.8		1.1		0.8
Weighted-average grant-date fair value (per award)	$	24.18	$	21.87	$	22.07
Total fair value of vested awards distributed	$	22.6	$	17.5	$	18.8
Cash-Settled Awards:
Awards granted	0.0		0.1		0.1
Weighted-average grant-date fair value (per award)	$	23.33	$	22.54	$	20.46
Total fair value of vested awards distributed	$	0.9	$	0.7	$	0.2
Performance-Based Awards:
Awards granted	4.8		3.3		2.9
Weighted-average grant-date fair value (per award)	$	20.06	$	19.58	$	20.88
Total fair value of vested awards distributed	$	112.4	$	27.9	$	18.7

In conjunction with common stock dividends declared in 2017 and 2016, we accrued dividends of $1.5 and $1.3, respectively, on non-vested stock-settled awards and paid dividends of $1.2 and $0.6 for stock-settled awards that vested during 2017 and 2016, respectively.

A summary of the activity of our non-vested stock-settled awards, cash-settled awards and performance-based awards during 2017 is presented below (performance-based awards are shown at 100% of the shares originally granted).



	Stock-Settled Awards					Cash-Settled Awards				Performance-Based Awards
	Awards			Weighted- Average Grant-Date Fair Value (per award)		Awards		Weighted- Average Grant-Date Fair Value (per award)		Awards			Weighted- Average Grant-Date Fair Value (per award)
Non-vested as of January 1, 2017	2.3			$	20.84	0.1		$	20.49	8.5			$	19.16
Granted	0.8			24.18		0.0		23.33		4.8			20.06
Vested	(1.0		)	19.49		0.0		19.27		(4.6		)	16.64
Forfeited	0.0			21.86		0.0		20.50		(0.4		)	20.00
Non-vested as of December 31, 2017	2.1			$	22.78	0.1		$	22.52	8.3			$	21.05
Total unrecognized compensation expense remaining	$	24.1				$	1.0			$	71.9
Weighted-average years expected to be recognized over	1.0					1.0				1.7

In conjunction with our annual grant of long-term incentive compensation awards, we reviewed our estimates and assumptions in 2017, which resulted in a forfeiture rate consistent with prior years.

2009 Restricted Cash Plan

In March 2009, the Compensation Committee approved the Interpublic Restricted Cash Plan (the “Cash Plan”). Under the Cash Plan, the Board, the Compensation Committee or the Plan Administrator may grant cash awards to certain employees eligible to receive stock-settled and cash-settled awards. Cash awards, when granted, have a service-period vesting condition and generally vest in three years.

Cash Awards

During the years ended December 31, 2017, 2016 and 2015, the Compensation Committee granted cash awards under the Cash Plan with a total target value of $2.8, $5.2 and $1.3, respectively. For those same years, we recognized $2.5, $3.1 and $3.0, respectively, in salaries and related expenses in our Consolidated Statements of Operations.

During the years ended December 31, 2017, 2016 and 2015, the Compensation Committee granted performance awards to be settled in cash under the 2014 PIP with a total target value of $38.4, $37.4, and $31.8, respectively. For those same years, we recognized $35.3, $39.8 and $35.8, respectively, in salaries and related expenses in our Consolidated Statements of Operations.

We amortize the present value of the amount expected to vest for cash awards and performance cash awards over the vesting period using the straight-line method, less an assumed forfeiture rate. Cash awards do not fall within the scope of the authoritative guidance for stock compensation as they are not paid in equity and the value of the award is not correlated with our stock price. Due to the cash nature of the payouts and the vesting period, we account for these awards in accordance with authoritative guidance for deferred compensation arrangements.

Employee Stock Purchase Plans

In May 2016, our shareholders approved The Interpublic Group of Companies Employee Stock Purchase Plan (2016) (the “ESPP”), replacing the prior employee stock purchase plan under which, prior to its expiration on December 31, 2015, 3.0 shares were issued. Under the ESPP, eligible employees may purchase our common stock through payroll deductions not exceeding 10% of their eligible compensation or 900 (actual number) shares each offering period, consistent with the prior employee stock purchase plan. The price an employee pays for a share of common stock under the ESPP is 90% of the lesser of the average market price of a share on the first business day of the offering period or the average market price of a share on the last business day of the offering period of three months. An aggregate of 10.0 shares are reserved for issuance under the ESPP, of which 0.5 shares have been issued through December 31, 2017.

Fair Value Measurements (Notes)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Fair Value Disclosures

Fair Value Measurements

Authoritative guidance for fair value measurements establishes a fair value hierarchy which requires us to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. There are three levels of inputs that may be used to measure fair value:



Level 1		Unadjusted quoted prices in active markets for identical assets or liabilities. An active market for the asset or liability is a market in which transactions for the asset or liability occur with sufficient frequency and volume to provide pricing information on an ongoing basis.

Level 2		Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3		Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

Financial Instruments that are Measured at Fair Value on a Recurring Basis

We primarily apply the market approach to determine the fair value of financial instruments that are measured at fair value on a recurring basis. There were no changes to our valuation techniques used to determine the fair value of financial instruments during 2017 as compared to the prior year.

The following tables present information about our financial instruments measured at fair value on a recurring basis as of December 31, 2017 and 2016, and indicates the fair value hierarchy of the valuation techniques utilized to determine such fair value.



	December 31, 2017								Balance Sheet Classification
	Level 1		Level 2		Level 3		Total		Balance Sheet Classification
Assets
Cash equivalents	$	201.6	$	0.0	$	0.0	$	201.6	Cash and cash equivalents

Liabilities
Contingent acquisition obligations ¹	$	0.0	$	0.0	$	147.0	$	147.0

	December 31, 2016								Balance Sheet Classification
	Level 1		Level 2		Level 3		Total		Balance Sheet Classification
Assets
Cash equivalents	$	440.8	$	0.0	$	0.0	$	440.8	Cash and cash equivalents

Liabilities
Contingent acquisition obligations ¹	$	0.0	$	0.0	$	205.4	$	205.4

Contingent acquisition obligations includes deferred acquisition payments and unconditional obligations to purchase additional noncontrolling equity shares of consolidated subsidiaries. Fair value measurement of the obligations is based upon actual and projected operating performance targets as specified in the related agreements. The decrease in this balance of $58.4 from December 31, 2016 to December 31, 2017 is primarily due to payments of $105.3, partially offset by acquisitions and exercised put options of $40.8. The amounts payable within the next twelve months are classified in accrued liabilities; any amounts payable thereafter are classified in other non-current liabilities.

Financial Instruments that are not Measured at Fair Value on a Recurring Basis

The following table presents information about our financial instruments that are not measured at fair value on a recurring basis as of December 31, 2017, and indicates the fair value hierarchy of the valuation techniques utilized to determine such fair value.



	December 31, 2017
	Level 1		Level 2		Level 3		Total
Total long-term debt	$	0.0	$	1,296.4	$	46.2	$	1,342.6

Our long-term debt is comprised of senior notes and other notes payable. The fair value of our senior notes, which are traded over-the-counter, is based on quoted prices in markets that are not active. Therefore, these senior notes are classified as Level 2 within the fair value hierarchy. Our other notes payable are not actively traded, and their fair value is not solely derived from readily observable inputs. The fair value of our other notes payable is determined based on a discounted cash flow model and other proprietary valuation methods, and therefore is classified as Level 3 within the fair value hierarchy. See Note 2 for further information on our long-term debt.

Non-financial Instruments that are Measured at Fair Value on a Nonrecurring Basis

Certain non-financial instruments are measured at fair value on a nonrecurring basis, primarily goodwill, intangible assets, and property and equipment. Accordingly, these assets are not measured and adjusted to fair value on an ongoing basis but are subject to periodic evaluations for potential impairment.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Employee Benefits (Notes)

12 Months Ended

Dec. 31, 2017

Retirement Benefits [Abstract]

Employee Benefits

Pension and Postretirement Benefit Plans

We have a defined benefit pension plan covering certain U.S. employees (the “Domestic Pension Plan”) that consists of approximately 3,500 participants and is closed to new participants. We also have numerous funded and unfunded plans outside the U.S. The Interpublic Limited Pension Plan in the U.K. (the "U.K. Pension Plan") is a defined benefit plan and is our most material foreign pension plan in terms of the benefit obligation and plan assets. The domestic postretirement benefit plan is our most material postretirement benefit plan in terms of the benefit obligation. This plan consists of approximately 1,700 participants, is closed to new participants and is unfunded.

Differences between the aggregate income statement and balance sheet amounts listed in the tables below and the totals reported in our Consolidated Statements of Operations, Consolidated Statements of Comprehensive Income and Consolidated Balance Sheets relate to non-material foreign pension and postretirement benefit plans.

From time to time, we evaluate the foreign plans to be included in the below disclosure based upon significance to our overall operations. Our evaluation consists of reviewing the Projected Benefit Obligation, Plan Assets and Funded Status of our plans to determine significance. As of December 31, 2017, the Funded Status of foreign plans that are not included in the below disclosure was in a deficit position of $56.2. The plans excluded from the below disclosure are comprised of numerous individually insignificant pension, postretirement and executive retirement plans, many of which are not required to be funded, in various foreign jurisdictions in which we operate. The effect of the change in scoping is noted within the Other caption within the tables below.

Pension and Postretirement Benefit Obligation

The change in the benefit obligation, the change in plan assets, the funded status and amounts recognized for the Domestic Pension Plan, the significant foreign pension plans and the domestic postretirement benefit plan are listed below.



	Domestic Pension Plan						Foreign Pension Plans						Domestic Postretirement Benefit Plan
	Domestic Pension Plan						Foreign Pension Plans						Domestic Postretirement Benefit Plan
Years ended December 31,	2017			2016			2017			2016			2017			2016
Benefit Obligation
Projected benefit obligation as of January 1	$	126.6		$	126.9		$	530.6		$	537.9		$	32.3		$	33.9
Service cost	0.0			0.0			4.9			6.7			0.0			0.0
Interest cost	5.1			5.9			13.5			15.1			1.3			1.5
Benefits paid	(11.4		)	(13.6		)	(19.0		)	(25.7		)	(5.9		)	(5.8		)
Plan participant contributions	0.0			0.0			0.2			0.2			1.6			1.6
Actuarial losses	5.1			7.4			20.3			115.6			2.5			1.1
Settlements and curtailments	0.0			0.0			(19.8		)	(6.3		)	0.0			0.0
Foreign currency effect	0.0			0.0			50.4			(84.2		)	0.0			0.0
Other	0.0			0.0			1.2			(28.7		)	0.0			0.0

Projected benefit obligation as of December 31	$	125.4		$	126.6		$	582.3		$	530.6		$	31.8		$	32.3

Fair Value of Plan Assets
Fair value of plan assets as of January 1	$	95.2		$	101.1		$	365.9		$	399.6		$	0.0		$	0.0
Actual return on plan assets	12.4			7.7			25.1			47.9			0.0			0.0
Employer contributions	2.6			0.0			17.5			23.2			4.3			4.2
Plan participant contributions	0.0			0.0			0.2			0.2			1.6			1.6
Benefits paid	(11.4		)	(13.6		)	(19.0		)	(25.7		)	(5.9		)	(5.8		)
Settlements	0.0			0.0			(19.1		)	(2.2		)	0.0			0.0
Foreign currency effect	0.0			0.0			33.2			(68.6		)	0.0			0.0
Other	0.0			0.0			0.4			(8.5		)	0.0			0.0
																0.0
Fair value of plan assets as of December 31	$	98.8		$	95.2		$	404.2		$	365.9		$	0.0		$	0.0

Funded status of the plans at December 31	$	(26.6	)	$	(31.4	)	$	(178.1	)	$	(164.7	)	$	(31.8	)	$	(32.3	)



	Domestic Pension Plan						Foreign Pension Plans						Domestic Postretirement Benefit Plan
December 31,	2017			2016			2017			2016			2017			2016
Amounts recognized in Consolidated Balance Sheets
Non-current asset	$	0.0		$	0.0		$	9.0		$	7.6		$	0.0		$	0.0
Current liability	0.0			0.0			(6.5		)	(5.5		)	(3.1		)	(3.2		)
Non-current liability	(26.6		)	(31.4		)	(180.6		)	(166.8		)	(28.7		)	(29.1		)

Net liability recognized	$	(26.6	)	$	(31.4	)	$	(178.1	)	$	(164.7	)	$	(31.8	)	$	(32.3	)

Accumulated benefit obligation	$	125.4		$	126.6		$	577.9		$	526.2

Amounts recognized in Accumulated Other Comprehensive Loss, net
Net actuarial loss	$	52.2		$	54.9		$	201.6		$	183.4		$	4.2		$	1.7
Prior service cost (credit)	0.0			0.0			1.1			0.9			(0.4		)	(0.6		)

Total amount recognized	$	52.2		$	54.9		$	202.7		$	184.3		$	3.8		$	1.1

In 2018, we estimate that we will recognize $1.5 and $6.0 of net actuarial losses from accumulated other comprehensive loss, net into net periodic cost related to our domestic pension plan and significant foreign pension plans, respectively.



	Domestic Pension Plan				Foreign Pension Plans
December 31,	2017		2016		2017		2016
Pension plans with underfunded or unfunded accumulated benefit obligation
Aggregate projected benefit obligation	$	125.4	$	126.6	$	576.6	$	525.3
Aggregate accumulated benefit obligation	125.4		126.6		575.2		523.8
Aggregate fair value of plan assets	98.8		95.2		389.5		352.9

Net Periodic Cost

The components of net periodic benefit cost and key assumptions are listed below.



	Domestic Pension Plan									Foreign Pension Plans									Domestic Postretirement Benefit Plan
Years ended December 31,	2017			2016			2015			2017			2016			2015			2017			2016			2015
Service cost	$	0.0		$	0.0		$	0.0		$	4.9		$	6.7		$	11.1		$	0.0		$	0.0		$	0.0
Interest cost	5.1			5.9			0.3			13.5			15.1			18.9			1.3			1.5			1.5
Expected return on plan assets	(6.2		)	(6.6		)	(7.6		)	(17.7		)	(18.7		)	(20.6		)	0.0			0.0			0.0
Settlement and curtailment losses (gains)	0.0			0.0			0.0			6.8			0.4			(0.2		)	0.0			0.0			0.0
Amortization of:
Prior service cost (credit)	0.0			0.0			0.0			0.1			0.1			0.1			(0.2		)	(0.2		)	(0.1		)
Net actuarial losses	1.5			1.3			6.5			5.5			4.2			4.1			0.0			0.0			0.0
Net periodic cost	$	0.4		$	0.6		$	(0.8	)	$	13.1		$	7.8		$	13.4		$	1.1		$	1.3		$	1.4

Assumptions



	Domestic Pension Plan						Foreign Pension Plans						Domestic Postretirement Benefit Plan
Years ended December 31,	2017		2016		2015		2017		2016		2015		2017		2016		2015

Net periodic cost
Discount rate	4.20	%	4.80	%	4.15	%	2.52	%	3.61	%	3.41	%	4.05	%	4.65	%	4.00	%
Rate of compensation increase	N/A		N/A		N/A		2.36	%	3.18	%	2.99	%	N/A		N/A		N/A
Expected return on plan assets	7.00	%	7.00	%	7.00	%	4.66	%	5.38	%	5.01	%	N/A		N/A		N/A

Benefit obligation
Discount rate	3.70	%	4.20	%	4.80	%	2.36	%	2.52	%	3.61	%	3.65	%	4.05	%	4.65	%
Rate of compensation increase	N/A		N/A		N/A		2.37	%	2.36	%	3.25	%	N/A		N/A		N/A

Health care cost trend rate assumed for next year
Initial rate (weighted-average)													6.50	%	6.75	%	7.00	%
Year ultimate rate is reached													2024		2024		2024
Ultimate rate													5.00	%	5.00	%	5.00	%

Discount Rates – At December 31, 2017, 2016 and 2015, we determined our discount rates for our Domestic Pension Plan, foreign pension plans and domestic postretirement benefit plan based on either a bond selection/settlement approach or bond yield curve approach. Using the bond selection/settlement approach, we determine the discount rate by selecting a portfolio of corporate bonds appropriate to provide for the projected benefit payments. Using the bond yield curve approach, we determine the discount rate by matching the plans' cash flows to spot rates developed from a yield curve. Both approaches utilize high-quality AA-rated corporate bonds and the plans' projected cash flows to develop a discounted value of the benefit payments, which is then used to develop a single discount rate. In countries where markets for high-quality long-term AA corporate bonds are not well developed, a portfolio of long-term government bonds is used as a basis to develop hypothetical corporate bond yields, which serve as a basis to derive the discount rate.

Expected Return on Assets – Our expected rate of return is determined at the beginning of each year and considers asset class index returns over various market and economic conditions, current and expected market conditions, risk premiums associated with asset classes and long-term inflation rates. We determine both a short-term and long-term view and then select a long-term rate of return assumption that matches the duration of our liabilities.

Fair Value of Pension Plan Assets

The following table presents the fair value of our domestic and foreign pension plan assets as of December 31, 2017 and 2016, and indicates the fair value hierarchy of the valuation techniques utilized to determine such fair value. See Note 10 for a description of the fair value hierarchy.



	December 31, 2017								December 31, 2016
Plan assets subject to fair value hierarchy	Level 1		Level 2		Level 3		Total		Level 1		Level 2		Level 3		Total
Registered investment companies	$	14.7	$	0.0	$	0.0	$	14.7	$	14.4	$	0.0	$	0.0	$	14.4
Limited partnerships	0.0		0.0		29.5		29.5		0.0		0.0		28.0		28.0
Fixed income securities	23.4		0.0		0.0		23.4		22.6		0.3		0.0		22.9
Insurance contracts	0.0		7.9		0.0		7.9		0.0		7.8		0.0		7.8
Other	27.7		0.0		0.0		27.7		20.1		0.0		0.0		20.1
Total plan assets, subject to leveling	$	65.8	$	7.9	$	29.5	$	103.2	$	57.1	$	8.1	$	28.0	$	93.2
Plan assets measured at net asset value
Other investments measured at net asset value ¹							399.8								367.9
Total plan assets							$	503.0							$	461.1


1	Certain investments that are measured at fair value using the net asset value per share (or its equivalent) as a practical expedient have not been classified in the fair value hierarchy but are included to reconcile to the amounts presented in the fair value of plan assets table above.

Registered investment companies, which are publicly traded, are primarily valued using recently reported sales prices. Limited partnerships are invested primarily in equity and fixed income securities. Fixed income securities include government and investment-grade corporate bonds. Insurance contracts are valued based on the cash surrender value of the contract. Other investments primarily include cash and cash equivalents, equity securities and derivatives. Other investments measured at net asset value include common/collective trusts, hedge funds and other commingled assets that are invested primarily in equity and fixed income securities. These investments are not publicly traded and are valued based on the net asset value of shares held by the plan at year end, which reflects the fair value of the underlying investments.

The following table presents additional information about our significant foreign pension plan assets for which we utilize Level 3 inputs to determine fair value.



	Years ended December 31,
Plan assets subject to fair value hierarchy, level 3	2017		2016
Balance at beginning of period	$	28.0	$	31.0
Actual return on plan assets	1.5		(3.0		)
Balance at end of period	$	29.5	$	28.0

Asset Allocation

The primary investment goal for our plans’ assets is to maximize total asset returns while ensuring the plans’ assets are available to fund the plans’ liabilities as they become due. The plans’ assets in aggregate and at the individual portfolio level are invested so that total portfolio risk exposure and risk-adjusted returns best achieve this objective. The aggregate amount of our own stock held as investment for our domestic and foreign pension funds is considered negligible relative to the total fund assets. As of December 31, 2017, the weighted-average target and actual asset allocations relating to our domestic and foreign pension plans' assets are listed below.



			December 31,
Asset Class	2018 Target Allocation		2017		2016
Alternative investments ¹	27	%	27	%	21	%
Equity securities	23	%	23	%	23	%
Fixed income securities	21	%	21	%	26	%
Liability driven investments ²	14	%	14	%	14	%
Real estate	6	%	6	%	6	%
Other	9	%	9	%	10	%
Total	100	%	100	%	100	%


1	Alternative investments have the flexibility to dynamically invest across a broad range of asset classes including bonds, equity, cash, property and commodities.


2	Liability driven investment strategies use government bonds as well as derivative instruments to hedge a portion of the impact of interest rates and inflation movements on the long-term liabilities.

Cash Flows

During 2017, we contributed $2.6 and $17.5 of cash to our domestic and foreign pension plans, respectively. For 2018, we expect to contribute approximately $10.0 and $18.0 of cash to our domestic and foreign pension plans, respectively.

The estimated future benefit payments expected to be paid are presented below.



Years	Domestic Pension Plan		Foreign Pension Plans		Domestic Postretirement Benefit Plan
2018	$	13.7	$	22.3	$	3.2
2019	8.5		23.8		3.0
2020	8.6		21.6		2.8
2021	8.0		22.3		2.6
2022	8.4		23.5		2.4
2023 - 2027	37.2		124.0		10.4

The estimated future payments for our domestic postretirement benefit plan are net of any estimated U.S. federal subsidies expected to be received under the Medicare Prescription Drug, Improvement and Modernization Act of 2003, which total no more than $0.3 in any individual year.

Savings Plans

We sponsor defined contribution plans (the “Savings Plans”) that cover substantially all domestic employees. The Savings Plans permit participants to make contributions on a pre-tax and/or after-tax basis and allow participants to choose among various investment alternatives. We match a portion of participant contributions based upon their years of service. Amounts expensed for the Savings Plans for 2017, 2016 and 2015 were $47.2, $47.0 and $44.5, respectively. Expenses include a discretionary Company contribution of $3.6, $6.1 and $5.8 offset by participant forfeitures of $4.6, $4.4 and $3.8 in 2017, 2016 and 2015, respectively. In addition, we maintain defined contribution plans in various foreign countries and contributed $47.4, $44.5 and $43.9 to these plans in 2017, 2016 and 2015, respectively.

Deferred Compensation and Benefit Arrangements

We have deferred compensation arrangements which (i) permit certain of our key officers and employees to defer a portion of their salary or incentive compensation or (ii) require us to contribute an amount to the participant’s account. The arrangements typically provide that the participant will receive the amounts deferred plus interest upon attaining certain conditions, such as completing a certain number of years of service or upon retirement or termination. As of December 31, 2017 and 2016, the deferred compensation liability balance was $96.2 and $92.4, respectively. Amounts expensed for deferred compensation arrangements in 2017, 2016 and 2015 were $11.2, $9.7 and $6.3, respectively.

We have deferred benefit arrangements with certain key officers and employees that provide participants with an annual payment, payable when the participant attains a certain age and after the participant’s employment has terminated. The deferred benefit liability was $117.0 and $129.1 as of December 31, 2017 and 2016, respectively. Amounts expensed for deferred benefit arrangements in 2017, 2016 and 2015 were $7.3, $8.8 and $9.7, respectively.

We have purchased life insurance policies on participants’ lives to assist in the funding of the related deferred compensation and deferred benefit liabilities. As of December 31, 2017 and 2016, the cash surrender value of these policies was $177.4 and $171.5, respectively. In addition to the life insurance policies, certain investments are held for the purpose of paying the deferred compensation and deferred benefit liabilities. These investments, along with the life insurance policies, are held in a separate revocable trust for the purpose of paying the deferred compensation and the deferred benefit arrangement liabilities. As of December 31, 2017 and 2016, the value of such investments in the trust was $15.9 and $12.9, respectively. The short-term investments are included in cash and cash equivalents, and the long-term investments and cash surrender value of the policies are included in other assets.

Long-Term Disability Plan

We have a long-term disability plan which provides income replacement benefits to eligible participants who are unable to perform their job duties or any job related to his or her education, training or experience. As all income replacement benefits are fully insured, no related obligation is required as of December 31, 2017 and 2016. In addition to income replacement benefits, plan participants may remain covered for certain health and life insurance benefits up to normal retirement age, and accordingly, we have recorded an obligation of $8.4 and $8.2 as of December 31, 2017 and 2016, respectively.

Segment Information (Notes)

12 Months Ended

Dec. 31, 2017

Segment Reporting [Abstract]

Segment Information

As of December 31, 2017, we have two reportable segments: IAN and CMG. IAN is comprised of McCann Worldgroup, Foote, Cone & Belding ("FCB"), MullenLowe Group, IPG Mediabrands, our digital specialist agencies and our domestic integrated agencies. CMG is comprised of a number of our specialist marketing services offerings. We also report results for the "Corporate and other" group.

Within IAN, our agencies provide a comprehensive array of global communications and marketing services, each offering a distinctive range of solutions for our clients. Our digital specialist agencies provide unique digital capabilities and service their own client rosters while also serving as key digital partners. In addition, our domestic integrated agencies, including Hill Holliday, Carmichael Lynch and Tierney, provide a full range of advertising, marketing communications services and/or marketing services and partner with our global operating divisions as needed. IAN’s operating divisions share similar economic characteristics and are similar in other areas, specifically related to the nature of their services, the manner in which the services are provided and the similarity of their respective customers.

CMG, which includes Weber Shandwick, DeVries, Golin, FutureBrand, Jack Morton and Octagon Worldwide, provides clients with diversified services, including public relations, meeting and event production, sports and entertainment marketing, corporate and brand identity, and strategic marketing consulting. CMG shares some similarities with service lines offered by IAN; however, on an aggregate basis, CMG has a higher proportion of arrangements for which they act as principal, a different distribution model than IAN and different margin structure.

The profitability measure employed by our chief operating decision maker for allocating resources to operating divisions and assessing operating division performance is operating income (loss). All segments follow the same accounting policies as those described in Note 1.

Certain corporate and other charges are reported as separate line items within total segment operating income and include corporate office expenses, shared service center expenses and certain other centrally managed expenses that are not fully allocated to operating divisions. Salaries and related expenses include salaries, long-term incentive awards, annual bonuses and other miscellaneous benefits for corporate office employees. Office and general expenses primarily include professional fees related to internal control compliance, financial statement audits and legal, information technology and other consulting services, which are engaged and managed through the corporate office. In addition, office and general expenses includes rental expense and depreciation of leasehold improvements for properties occupied by corporate office employees. A portion of centrally managed expenses are allocated to operating divisions based on a formula that uses the planned revenues of each of the operating units. Amounts allocated also include specific charges for information technology-related projects, which are allocated based on utilization.

Summarized financial information concerning our reportable segments is shown in the following tables.



	Years ended December 31,
	2017			2016			2015
Revenue:
IAN	$	6,397.3		$	6,319.4		$	6,145.4
CMG	1,485.1			1,527.2			1,468.4
Total	$	7,882.4		$	7,846.6		$	7,613.8

Segment operating income (loss):
IAN	$	907.4		$	898.2		$	850.3
CMG	192.8			190.0			166.3
Corporate and other	(126.6		)	(147.2		)	(141.8		)
Total	973.6			941.0			874.8

Interest expense	(90.8		)	(90.6		)	(85.8		)
Interest income	19.4			20.1			22.8
Other expense, net	(26.2		)	(40.3		)	(49.6		)
Income before income taxes	$	876.0		$	830.2		$	762.2

Depreciation and amortization of property, equipment and intangible assets:
IAN	$	111.8		$	117.7		$	117.5
CMG	20.4			19.5			18.4
Corporate and other	24.9			23.0			21.1
Total	$	157.1		$	160.2		$	157.0

Capital expenditures:
IAN	$	112.0		$	149.2		$	117.5
CMG	17.7			16.6			12.7
Corporate and other	26.2			34.9			30.9
Total	$	155.9		$	200.7		$	161.1

	December 31,
	2017			2016
Total assets:
IAN	$	10,973.0		$	10,660.0
CMG	1,422.9			1,428.3
Corporate and other	299.3			396.9
Total	$	12,695.2		$	12,485.2

Revenue and long-lived assets, excluding intangible assets, are presented by major geographic area in the following table.



	Revenue						Long-Lived Assets
	Years ended December 31,						December 31,
	2017		2016		2015		2017		2016
Domestic	$	4,714.3	$	4,684.8	$	4,475.5	$	705.5	$	684.8
International:
United Kingdom	681.8		695.7		687.7		56.2		52.0
Continental Europe	716.1		699.8		697.2		73.6		57.0
Asia Pacific	913.6		923.0		916.9		115.5		118.3
Latin America	355.9		372.7		383.5		48.2		49.0
Other	500.7		470.6		453.0		46.1		43.3
Total International	3,168.1		3,161.8		3,138.3		339.6		319.6
Total Consolidated	$	7,882.4	$	7,846.6	$	7,613.8	$	1,045.1	$	1,004.4

Revenue is primarily attributed to geographic areas based on where the services are performed. Property and equipment are allocated based upon physical location. Other assets and investments are allocated based on the location of the related operations.

Commitments and Contingencies (Notes)

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

Leases

We lease office premises and equipment. Where leases contain escalation clauses or concessions, such as rent holidays and landlord/tenant incentives or allowances, the impact of such adjustments is recognized on a straight-line basis over the minimum lease period. Certain leases provide for renewal options and require the payment of real estate taxes or other occupancy costs, which are also subject to escalation clauses. Net rent expense is listed in the table below.



	Years ended December 31,
	2017			2016			2015
Gross rent expense	$	371.0		$	366.1		$	336.5
Third-party sublease rental income	(4.6		)	(4.1		)	(5.5		)
Net rent expense	$	366.4		$	362.0		$	331.0

Cash amounts for future minimum lease commitments for office premises and equipment under non-cancelable leases, along with minimum sublease rental income to be received under non-cancelable subleases, are listed in the table below.



Period	Rent Obligations		Sublease Rental Income			Net Rent
2018	$	335.0	$	(4.2	)	$	330.8
2019	312.1		(3.8		)	308.3
2020	285.3		(2.5		)	282.8
2021	251.4		(1.4		)	250.0
2022	204.1		(0.8		)	203.3
Thereafter	727.2		(0.5		)	726.7
Total	$	2,115.1	$	(13.2	)	$	2,101.9

Guarantees

We have guaranteed certain obligations of our subsidiaries relating principally to operating leases and uncommitted lines of credit of certain subsidiaries. The amount of parent company guarantees on lease obligations was $829.2 and $857.3 as of December 31, 2017 and 2016, respectively, and the amount of parent company guarantees primarily relating to uncommitted lines of credit was $491.0 and $395.6 as of December 31, 2017 and 2016, respectively. In the event of non-payment by the applicable subsidiary of the obligations covered by a guarantee, we would be obligated to pay the amounts covered by that guarantee. As of December 31, 2017, there were no material assets pledged as security for such parent company guarantees.

Contingent Acquisition Obligations

The following table details the estimated future contingent acquisition obligations payable in cash as of December 31, 2017.



	2018		2019		2020		2021		2022		Thereafter		Total
Deferred acquisition payments	$	41.9	$	27.5	$	16.1	$	24.4	$	4.8	$	6.3	$	121.0
Redeemable noncontrolling interests and call options with affiliates ¹	37.1		26.4		62.9		10.3		6.6		4.1		147.4
Total contingent acquisition payments	$	79.0	$	53.9	$	79.0	$	34.7	$	11.4	$	10.4	$	268.4

We have entered into certain acquisitions that contain both redeemable noncontrolling interests and call options with similar terms and conditions. The estimated amounts listed would be paid in the event of exercise at the earliest exercise date. We have certain redeemable noncontrolling interests that are exercisable at the discretion of the noncontrolling equity owners as of December 31, 2017. These estimated payments of $24.8 are included within the total payments expected to be made in 2018, and will continue to be carried forward into 2019 or beyond until exercised or expired. Redeemable noncontrolling interests are included in the table at current exercise price payable in cash, not at applicable redemption value, in accordance with the authoritative guidance for classification and measurement of redeemable securities.

The majority of these payments are contingent upon achieving projected operating performance targets and satisfying other conditions specified in the related agreements and are subject to revision in accordance with the terms of the respective agreements. See Note 4 for further information relating to the payment structure of our acquisitions.

Legal Matters

In the normal course of business, we are involved in various legal proceedings, and subject to investigations, inspections, audits, inquiries and similar actions by governmental authorities. The types of allegations that arise in connection with such legal proceedings vary in nature, but can include claims related to contract, employment, tax and intellectual property matters. We evaluate all cases each reporting period and record liabilities for losses from legal proceedings when we determine that it is probable that the outcome in a legal proceeding will be unfavorable and the amount, or potential range, of loss can be reasonably estimated. In certain cases, we cannot reasonably estimate the potential loss because, for example, the litigation is in its early stages. While any outcome related to litigation or such governmental proceedings in which we are involved cannot be predicted with certainty, management believes that the outcome of these matters, individually and in the aggregate, will not have a material adverse effect on our financial condition, results of operations or cash flows.

As previously disclosed, on April 10, 2015, a federal judge in Brazil authorized the search of the records of an agency's offices in São Paulo and Brasilia, in connection with an ongoing investigation by Brazilian authorities involving payments potentially connected to local government contracts. The Company had previously investigated the matter and taken a number of remedial and disciplinary actions. The Company is in the process of concluding a settlement related to these matters with government agencies.

The Company confirmed that one of its standalone domestic agencies has been contacted by the Department of Justice Antitrust Division for documents regarding video production practices and is cooperating with the government.

Recent Accounting Standards (Notes)	12 Months Ended
Recent Accounting Standards (Notes)	Dec. 31, 2017
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recent Accounting Standards	Recent Accounting Standards Accounting pronouncements not listed below were assessed and determined to be not applicable or are expected to have minimal impact on our Consolidated Financial Statements. Derivatives and Hedging In August 2017, the Financial Accounting Standards Board (the "FASB") issued amended guidance on hedge accounting which expands an entity’s ability to hedge non-financial and financial risk components and aligns the recognition and presentation of the effects of the hedging instrument and the hedged item in the financial statements. The new guidance also eliminates the requirement to separately measure and report hedge ineffectiveness. This amended guidance is effective beginning January 1, 2019, with early adoption permitted. We are currently assessing the impact the adoption of the amended guidance will have on our Consolidated Financial Statements. Pensions In March 2017, the FASB issued amended guidance which requires presentation of all net periodic pension and postretirement benefit costs, other than service costs, in non-operating expenses in the Consolidated Statement of Operations. We have early adopted this amended guidance retrospectively as of the quarter ended March 31, 2017 using the practical expedient, which permits the use of amounts disclosed in our Employee Benefits note for prior comparative periods as the estimation basis for applying the retrospective presentation requirements. This resulted in the reclassification of a portion of postretirement costs from "Salaries and related expenses" to "Other expense, net" in the amount of $9.6, $3.0 and $2.9 for the years ended December 31, 2017, 2016 and 2015, respectively. Restricted Cash In November 2016, the FASB issued amended guidance which requires that the Consolidated Statement of Cash Flows present the change during the period in the total cash, cash equivalents and amounts generally described as restricted cash or restricted cash equivalents. We have early adopted this amended guidance retrospectively as of the quarter ended March 31, 2017. The Consolidated Statements of Cash Flows now reflect the inclusion and activity of restricted cash balances of $6.8, $2.6, $3.2 and $3.8 as of December 31, 2017, 2016, 2015 and 2014, respectively. Financial Instrument Credit Losses In June 2016, the FASB issued amended guidance on the accounting for credit losses on certain types of financial instruments, including trade receivables. The new model uses a forward-looking expected loss method, as opposed to the incurred loss method in current U.S. GAAP, which will generally result in earlier recognition of allowances for losses. This amended guidance is effective beginning January 1, 2020, with early adoption permitted as early as January 1, 2019. We are currently assessing the impact the adoption of the amended guidance will have on our Consolidated Financial Statements. Leases In February 2016, the FASB issued amended guidance on lease accounting which requires an entity to recognize a right-of-use asset and a corresponding lease liability on its balance sheet for virtually all of its leases with a term of more than 12 months, including those classified as operating leases. Both the asset and liability will initially be measured at the present value of the future minimum lease payments, with the asset being subject to adjustments such as initial direct costs. Consistent with current U.S. GAAP, the presentation of expenses and cash flows will depend primarily on the classification of the lease as either a finance or an operating lease. The new standard also requires additional quantitative and qualitative disclosures regarding the amount, timing and uncertainty of cash flows arising from leases in order to provide additional information about the nature of an organization’s leasing activities. This amended guidance, which will be effective beginning January 1, 2019, requires modified retrospective application, with early adoption permitted. We expect the adoption of this amended guidance to have a significant impact on our Consolidated Balance Sheets but not on our Consolidated Statements of Operations. Fair Value Measurements In January 2016, the FASB issued amended guidance which updates the fair value presentation requirements for certain financial instruments. Equity investments with readily determinable fair values, other than those accounted for using the equity method of accounting, will be measured at fair value with changes recorded through current earnings rather than other comprehensive income. This amended guidance will be effective for us beginning January 1, 2018, and is required to be adopted prospectively with a cumulative-effect adjustment recorded on our Consolidated Balance Sheets, if applicable. We do not expect the adoption of this amended guidance to have a significant impact on our Consolidated Financial Statements. Revenue Recognition In May 2014, the FASB issued amended guidance on revenue recognition which requires an entity to recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods and services. We have elected to adopt the standard, effective January 1, 2018, using the full retrospective method. The standard, which accelerates the recognition of revenue primarily as a result of estimating variable consideration, mostly impacts the timing of revenue recognition between quarters, but also can affect, to a lesser extent, the amount of annual revenue recognized. Although we have determined that the standard results in an increase in the number of performance obligations within certain of our contractual arrangements, this is not expected to materially impact the amount or timing of revenue recognized. The standard will also result in an increase in third party costs of approximately $1,100.0 to $1,300.0 being included in revenue and costs, primarily in connection with our events businesses, which has no impact on operating income, net income or cash flows. The increase to retained earnings as of December 31, 2017 as a result of adopting the standard is not material.

Results by Quarter (Unaudited) (Notes)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Information

Results by Quarter (Unaudited)



	Three Months Ended March 31,						Three Months Ended June 30,						Three Months Ended September 30,						Three Months Ended December 31,
	2017			2016			2017			2016			2017			2016			2017			2016
Revenue	$	1,753.9		$	1,742.0		$	1,884.9		$	1,917.9		$	1,902.6		$	1,922.2		$	2,341.0		$	2,264.5
Salaries and related expenses ¹	1,275.4			1,268.8			1,239.3			1,229.5			1,227.6			1,228.0			1,325.8			1,308.8
Office and general expenses	448.8			450.2			439.1			464.1			455.9			486.2			496.9			470.0
Operating income	29.7			23.0			206.5			224.3			219.1			208.0			518.3			485.7
Other income (expense), net ^1,2	0.8			(19.2		)	(15.4		)	0.4			(9.9		)	5.3			(1.7		)	(26.8		)
Total (expenses) and other income	(14.9		)	(36.0		)	(36.4		)	(18.5		)	(26.8		)	(11.7		)	(19.5		)	(44.6		)
(Benefit of) provision for income taxes ³	(2.1		)	(15.6		)	75.4			43.7			42.5			63.8			166.1			106.1
Net income	18.1			2.7			94.6			160.2			148.8			132.7			333.5			336.9
Net income available to IPG common stockholders	$	21.5		$	5.4		$	94.7		$	156.9		$	146.2		$	128.6		$	316.6		$	317.6

Earnings per share available to IPG common stockholders:
Basic	$	0.05		$	0.01		$	0.24		$	0.39		$	0.38		$	0.32		$	0.82		$	0.81
Diluted	$	0.05		$	0.01		$	0.24		$	0.38		$	0.37		$	0.32		$	0.81		$	0.78

Dividends declared per common share	$	0.18		$	0.15		$	0.18		$	0.15		$	0.18		$	0.15		$	0.18		$	0.15


1	As part of the adoption of FASB ASU 2017-07, we have reclassified a portion of postretirement costs from salaries and related expenses to other income (expense), net.


2	The three months ended June 30 and September 30, 2017 included pre-tax net losses of $13.1 and $8.7, respectively, on sales of businesses. The three months ended March 31 and December 31, 2016 included pre-tax net losses of $16.3 and $25.3, respectively, on sales of businesses.

The three months ended September 30, 2017 included a tax benefit of $31.2 related to foreign tax credits from distributions of unremitted earnings, which was reversed during the three months ended December 31, 2017 as a result of the enactment of the Tax Cuts and Jobs Act. The three months ended December 31, 2017 included a net tax benefit of $36.0 as a result of the enactment of the Tax Cuts and Jobs Act. The three months ended March 31, 2016 included a tax benefit of $12.2 due to the reversal of valuation allowances. The three months ended June 30, 2016 included a tax benefit of $23.4 related to the conclusion and settlement of a tax examination of previous years. The three months ended December 31, 2016 included a tax benefit of $37.4 for refunds to be claimed on future amended U.S. federal returns.

Subsequent Events (Notes)	12 Months Ended
Subsequent Events (Notes)	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events [Text Block]	Subsequent Events In February 2018, we announced that our Board had approved a new share repurchase program to repurchase from time to time up to $300.0, excluding fees, of our common stock (the "2018 Share Repurchase Program"). The authorization for repurchases under the 2018 Share Repurchase Program is in addition to any amounts remaining for repurchase under the 2017 Share Repurchase Program. See Note 5 for further information on the 2017 Share Repurchase Program. There is no expiration date associated with the share repurchase programs. We may effect such repurchases through open market purchases, trading plans established in accordance with SEC rules, derivative transactions or other means. We expect to continue to repurchase our common stock in future periods, although the timing and amount of the repurchases will depend on market conditions and other funding requirements. We also announced in February 2018 that our Board had declared a common stock cash dividend of $0.21 per share, payable on March 15, 2018 to holders of record as of the close of business on March 1, 2018.

Significant Accounting Policies Principles of Consolidation (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The Consolidated Financial Statements include the accounts of the Company and its consolidated subsidiaries, some of which are not wholly owned. Investments in companies over which we do not have control, but have the ability to exercise significant influence, are accounted for using the equity method of accounting. Investments in companies over which we have neither control nor have the ability to exercise significant influence are accounted for under the cost method. All intercompany accounts and transactions have been eliminated in consolidation. We have consolidated certain entities meeting the definition of variable interest entities, and the inclusion of these entities does not have a material impact on our Consolidated Financial Statements.

Significant Accounting Policies Reclassifications (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Reclassifications	Reclassifications Certain reclassifications and immaterial revisions have been made to the prior period financial statements to conform to the current-year presentation. We plan to adopt a new presentation for our Consolidated Statements of Operations beginning the first quarter of 2018 which will separately present Cost of services; Selling, general and administrative expenses; and Depreciation and amortization within our Operating expenses. For the years ended December 31, 2017 and 2016, our Selling, general and administrative expenses were $118.6 and $138.8, respectively, which are primarily the expenses of our “Corporate and other” group, as disclosed further in Note 12, excluding depreciation and amortization. For the years ended December 31, 2017 and 2016, Depreciation and amortization were $157.1 and $160.2, respectively, which is also presented on the Consolidated Statements of Cash Flows. This change in presentation of expenses does not impact total operating expenses or operating income.

Significant Accounting Policies Use of Estimates (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) requires us to make judgments, assumptions and estimates that affect the amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the reporting date and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from these estimates and assumptions.

Significant Accounting Policies Revenue Recognition (Policies)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Revenue Recognition

•


•	Fees are recognized on a straight-line or monthly basis when service is provided essentially on a pro-rata basis and the terms of the contract support monthly basis accounting.

•

Significant Accounting Policies Cash and Cash Equivalents (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Cash and Cash Equivalents	Cash and Cash Equivalents Cash equivalents are highly liquid investments, which include certificates of deposit, government securities, commercial paper and time deposits with original maturities of three months or less at the time of purchase and are stated at estimated fair value, which approximates cost. Cash is maintained at multiple high-credit-quality financial institutions.

Significant Accounting Policies Allowance for Doubtful Accounts (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Allowance for Doubtful Accounts	Allowance for Doubtful Accounts The allowance for doubtful accounts is estimated based on the aging of accounts receivable, reviews of client credit reports, industry trends and economic indicators, as well as reviews of recent payment history for specific customers. The estimate is based largely on a formula-driven calculation but is supplemented with economic indicators and knowledge of potential write-offs of specific client accounts.

- Definition

Disclosure of accounting policy for trade and other accounts receivable, and finance, loan and lease receivables, including those classified as held for investment and held for sale. This disclosure may include (1) the basis at which such receivables are carried in the entity's statements of financial position (2) how the level of the valuation allowance for receivables is determined (3) when impairments, charge-offs or recoveries are recognized for such receivables (4) the treatment of origination fees and costs, including the amortization method for net deferred fees or costs (5) the treatment of any premiums or discounts or unearned income (6) the entity's income recognition policies for such receivables, including those that are impaired, past due or placed on nonaccrual status and (7) the treatment of foreclosures or repossessions (8) the nature and amount of any guarantees to repurchase receivables.

+ References + Details

Significant Accounting Policies Expenditures Billable to Clients (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Expenditures Billable to Clients	Expenditures Billable to Clients Expenditures billable to clients are primarily comprised of production and media costs that have been incurred but have not yet been billed to clients, as well as fees that have been earned which have not yet been billed to clients. Unbilled amounts are presented in expenditures billable to clients regardless of whether they relate to our fees or production and media costs. A provision is made for unrecoverable costs as deemed appropriate.

Significant Accounting Policies Investments (Policies)	12 Months Ended
Significant Accounting Policies Investments (Policies)	Dec. 31, 2017
Accounting Policies [Abstract]
Investments	Investments Our investments in short-term marketable securities include investment-grade time deposits, commercial paper, government securities with maturities greater than three months but less than twelve months and publicly traded companies over which we do not exert a significant influence. These investments are classified as available-for-sale and reported at fair value based on quoted market prices with net unrealized gains and losses reported as a component of accumulated other comprehensive loss. Our non-publicly traded investments and all other publicly traded investments, including investments to fund certain deferred compensation and retirement obligations, are accounted for using the equity method or cost method. We do not disclose the fair value for all equity method investments or investments held at cost as it is not practical to estimate fair value since there is no readily available market data and it is cost prohibitive to obtain independent valuations. We regularly review our equity and cost method investments to determine whether a significant event or change in circumstances has occurred that may impact the fair value of each investment. In the event a decline in fair value of an investment occurs, we determine if the decline has been other-than-temporary. We consider our investments strategic and long-term in nature, so we determine if the fair value decline is recoverable within a reasonable period. For our investments, we evaluate fair value based on specific information (valuation methodologies, estimates of appraisals, financial statements, etc.) in addition to quoted market price, if available. We consider all known quantitative and qualitative factors in determining if an other-than-temporary decline in value of an investment has occurred.

- Definition

Disclosure of accounting policy for investments in financial assets, including marketable securities (debt and equity securities with readily determinable fair values), investments accounted for under the equity method and cost method, securities borrowed and loaned, and repurchase and resale agreements. For marketable securities, the disclosure may include the entity's accounting treatment for transfers between investment categories and how the fair values for such securities are determined. Also, for all investments, an entity may describe its policy for assessing, recognizing and measuring impairment of the investment.

+ References + Details

Significant Accounting Policies Derivatives (Policies)	12 Months Ended
Significant Accounting Policies Derivatives (Policies)	Dec. 31, 2017
Accounting Policies [Abstract]
Derivatives	Derivatives We are exposed to market risk related to interest rates, foreign currency rates and certain balance sheet items. From time to time we enter into derivative instruments for risk management purposes, and not for speculative purposes. All derivative instruments are recorded at fair value on our balance sheet. Changes in fair value are immediately included in earnings if the derivatives are not designated as a hedge instrument or if the derivatives do not qualify as effective hedges. For derivatives designated as hedge instruments, we evaluate for hedge accounting both at inception and throughout the hedge period. If a derivative is designated as a fair value hedge, then changes in the fair value of the derivative are offset against the changes in the fair value of the underlying hedged item. If a derivative is designated as a cash flow hedge, then the effective portion of the changes in the fair value of the derivative is recognized as a component of accumulated other comprehensive income and subsequently reclassified to earnings in our Consolidated Statement of Operations in the same period as the underlying hedged transaction affects earnings.

Significant Accounting Policies Property and Equipment (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Property and Equipment	Property and Equipment Furniture, equipment, leasehold improvements and buildings are stated at cost, net of accumulated depreciation. Furniture and equipment are depreciated generally using the straight-line method over the estimated useful lives of the related assets, which range from 3 to 7 years for furniture and equipment, 10 to 35 years for buildings and the shorter of the useful life or the remaining lease term for leasehold improvements. Land is stated at cost and is not depreciated. We capitalize certain internal and external costs incurred to acquire or create internal use software, principally related to our enterprise resource planning (“ERP”) systems. Our ERP systems are stated at cost, net of accumulated amortization, and are amortized using the straight-line method over 10 years. All other internal use computer software are stated at cost, net of accumulated amortization and are amortized using the straight-line method over the estimated useful lives of the related assets, which range from 3 to 7 years.

Significant Accounting Policies Goodwill and Other Intangible Assets (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets We account for our business combinations using the acquisition accounting method, which requires us to determine the fair value of net assets acquired and the related goodwill and other intangible assets. Determining the fair value of assets acquired and liabilities assumed requires management's judgment and involves the use of significant estimates, including projections of future cash inflows and outflows, discount rates, asset lives and market multiples. Considering the characteristics of advertising, specialized marketing and communication services companies, our acquisitions usually do not have significant amounts of tangible assets, as the principal asset we typically acquire is creative talent. As a result, a substantial portion of the purchase price is allocated to goodwill and other intangible assets. We review goodwill and other intangible assets with indefinite lives not subject to amortization as of October 1^st each year and whenever events or significant changes in circumstances indicate that the carrying value may not be recoverable. We evaluate the recoverability of goodwill at a reporting unit level. We have 11 reporting units that were subject to the 2017 annual impairment testing. Our annual impairment review as of October 1, 2017 did not result in an impairment charge for any of our reporting units. For reporting units not included in the qualitative assessment, or for any reporting units identified in the qualitative assessment as "more likely than not" that the fair value is less than its carrying value, the quantitative impairment test is performed. For our annual impairment test, we compare the respective fair value of our reporting units' equity to the carrying value of their net assets. The sum of the fair values of all our reporting units is also reconciled to our current market capitalization plus an estimated control premium. Goodwill allocated to a reporting unit whose fair value is equal to or greater than its carrying value is not impaired, and no further testing is required. Should the carrying amount for a reporting unit exceed its fair value, then the quantitative impairment test is failed and impaired goodwill is written down to its fair value with a charge to expense in the period the impairment is identified. The fair value of each reporting unit for 2017 and 2016 was estimated using a combination of the income approach, which incorporates the use of the discounted cash flow method, and the market approach, which incorporates the use of earnings and revenue multiples based on market data. We review intangible assets with definite lives subject to amortization whenever events or circumstances indicate that a carrying amount of an asset may not be recoverable. Recoverability of these assets is determined by comparing the carrying value of these assets to the estimated undiscounted future cash flows expected to be generated by these assets. These assets are impaired when their carrying value exceeds their fair value. Impaired intangible assets with definite lives subject to amortization are written down to their fair value with a charge to expense in the period the impairment is identified. Intangible assets with definite lives are amortized on a straight-line basis with estimated useful lives generally between 7 and 15 years. Events or circumstances that might require impairment testing include the loss of a significant client, the identification of other impaired assets within a reporting unit, loss of key personnel, the disposition of a significant portion of a reporting unit, significant decline in stock price or a significant adverse change in business climate or regulations.

Significant Accounting Policies Foreign Currencies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Foreign Currencies	Foreign Currencies The functional currency of our foreign operations is generally their respective local currency. Assets and liabilities are translated at the exchange rates in effect at the balance sheet date, and revenues and expenses are translated at the average exchange rates during the period presented. The resulting translation adjustments are recorded as a component of accumulated other comprehensive loss in the stockholders’ equity section of our Consolidated Balance Sheets. Currency transaction gains or losses primarily arising from transactions in currencies other than the functional currency are included in office and general expenses. Foreign currency transactions resulted in pre-tax gains of $1.9, $2.1 and $2.0 in for the years ended December 31, 2017, 2016 and 2015, respectively. We monitor the currencies of countries in which we operate in order to determine if the country should be considered a highly inflationary environment. A currency is determined to be highly inflationary when there is cumulative inflation of approximately 100% or more over a three-year period. If this occurs the functional currency of that country would be changed to our reporting currency, the U.S. Dollar, and foreign exchange gains or losses would be recognized on all monetary transactions, assets and liabilities in currencies other than the U.S. Dollar until the currency is no longer considered highly inflationary.

Significant Accounting Policies Income Taxes (Policies)	12 Months Ended
Significant Accounting Policies Income Taxes (Policies)	Dec. 31, 2017
Accounting Policies [Abstract]
Income Taxes	Income Taxes The provision for income taxes includes U.S. federal, state, local and foreign taxes. Income taxes are accounted for under the liability method. Deferred tax assets and liabilities are recognized for the estimated future tax consequences of temporary differences between the financial statement carrying amounts and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the year in which the temporary differences are expected to be reversed. We evaluate the realizability of our deferred tax assets and establish a valuation allowance when it is “more likely than not” that all or a portion of the deferred tax assets will not be realized. We evaluate our tax positions using the “more likely than not” recognition threshold and then apply a measurement assessment to those positions that meet the recognition threshold. The factors used in assessing valuation allowances include all available evidence, such as past operating results, estimates of future taxable income and the feasibility of tax planning strategies. We have established tax reserves that we believe to be adequate in relation to the potential for additional assessments in each of the jurisdictions in which we are subject to taxation. We regularly assess the likelihood of additional tax assessments in those jurisdictions and adjust our reserves as additional information or events require. In response to the enactment of the Tax Act, the SEC issued SAB 118 on December 22, 2017, which acknowledges that the information necessary to determine such income tax effects may not be sufficiently available, prepared or analyzed in reasonable detail to complete the accounting under U.S. GAAP. SAB 118 allows for the reporting of provisional amounts for those specific tax effects for which a reasonable estimate can be made, and for no amounts to be recorded where a reasonable estimate cannot be made. Any subsequent adjustments to reported amounts will be made over the measurement period, which begins in the reporting period that includes the Tax Act's enactment date and ends when an entity has obtained, prepared and analyzed the information that is needed in order to complete the accounting requirements under U.S. GAAP, not to exceed one year from the enactment date. We have reasonably estimated and recorded provisional amounts resulting from the enactment of the Tax Act. Refer to Note 7 to our Consolidated Financial Statements for further information.

- Definition

Disclosure of accounting policy for income taxes, which may include its accounting policies for recognizing and measuring deferred tax assets and liabilities and related valuation allowances, recognizing investment tax credits, operating loss carryforwards, tax credit carryforwards, and other carryforwards, methodologies for determining its effective income tax rate and the characterization of interest and penalties in the financial statements.

+ References + Details

Significant Accounting Policies Redeemable Noncontrolling Interests (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Redeemable Noncontrolling Interests	Redeemable Noncontrolling Interests Many of our acquisitions include provisions under which the noncontrolling equity owners can require us to purchase additional interests in a subsidiary at their discretion. Payments for these redeemable noncontrolling interests may be contingent on projected operating performance and satisfying other conditions specified in the related agreements. These payments are also subject to revision in accordance with the terms of the agreements. We record these redeemable noncontrolling interests in “mezzanine equity” in our Consolidated Balance Sheets. Each reporting period, redeemable noncontrolling interests are reported at their estimated redemption value, but not less than their initial fair value. Any adjustment to the redemption value above initial value prior to exercise will also impact retained earnings or additional paid-in capital (“APIC”), but will not impact net income. Adjustments as a result of currency translation will affect the redeemable noncontrolling interest balance, but do not impact retained earnings or additional paid-in capital.

Significant Accounting Policies Earnings Per Share (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Earnings Per Share	Earnings Per Share (“EPS”) Basic EPS available to IPG common stockholders equals net income available to IPG common stockholders divided by the weighted-average number of common shares outstanding for the applicable period. Diluted EPS equals net income available to IPG common stockholders divided by the weighted-average number of common shares outstanding, plus any additional common shares that would have been outstanding if potentially dilutive shares had been issued. Diluted EPS reflect the potential dilution that would occur if certain potentially dilutive securities were exercised. The potential issuance of common stock is assumed to occur at the beginning of the year (or at the time of issuance of the potentially dilutive instrument, if later) and the incremental shares are included using the treasury stock method. The proceeds utilized in applying the treasury stock method consist of the amount, if any, to be paid upon exercise and, as it relates to stock-based compensation, the amount of compensation cost attributed to future service not yet recognized. These proceeds are then assumed to be used to purchase common stock at the average market price of our stock during the period. The incremental shares (difference between the shares assumed to be issued and the shares assumed to be purchased), to the extent they would have been dilutive, are included in the denominator of the diluted EPS calculation. We may be required to calculate basic EPS using the two-class method as a result of our redeemable noncontrolling interests. To the extent that the redemption value increases and exceeds the then-current fair value of a redeemable noncontrolling interest, net income available to IPG common stockholders (used to calculate EPS) could be negatively impacted by that increase, subject to certain limitations. The partial or full recovery of any reductions to net income available to IPG common stockholders (used to calculate EPS) is limited to any cumulative prior-period reductions. For the years ended December 31, 2017, 2016 and 2015, there was no impact to EPS for adjustments related to our redeemable noncontrolling interests.

Significant Accounting Policies Pension and Postretirement Benefits (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Pension and Postretirement Benefits	Pension and Postretirement Benefits We have pension and postretirement benefit plans covering certain domestic and international employees. We use various actuarial methods and assumptions in determining our net pension and postretirement benefit costs and obligations, including the discount rate used to determine the present value of future benefits, expected long-term rate of return on plan assets and healthcare cost trend rates. The overfunded or underfunded status of our pension and postretirement benefit plans is recorded on our Consolidated Balance Sheet.

- Definition

Disclosure of accounting policy for pension and other postretirement benefit plans. This accounting policy may address (1) the types of plans sponsored by the entity, and the benefits provided by each plan (2) groups that participate in (or are covered by) each plan (3) how plan assets, liabilities and expenses are measured, including the use of any actuaries and (4) significant assumptions used by the entity to value plan assets and liabilities and how such assumptions are derived.

+ References + Details

Significant Accounting Policies Stock-Based Compensation (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Stock-Based Compensation	Stock-Based Compensation Compensation costs related to share-based transactions, including employee stock options, are recognized in the Consolidated Financial Statements based on fair value. Stock-based compensation expense is generally recognized ratably over the requisite service period based on the estimated grant-date fair value, net of estimated forfeitures.

Significant Accounting Policies Treasury Stock (Policies)	12 Months Ended
	Dec. 31, 2017
Treasury Stock, Shares [Abstract]
Treasury Stock [Text Block]	Treasury Stock We account for repurchased common stock under the cost method and include such treasury stock as a component of our Consolidated Statements of Stockholders' Equity. Upon retirement, we reduce common stock for the par value of the shares being retired and the excess of the cost of the shares over par value as a reduction to APIC, to the extent there is APIC in the same class of stock, and any remaining amount to retained earnings. These retired shares remain authorized but unissued. In October and November 2017, we retired 13.4 shares of our treasury stock, which resulted in a reduction in common stock of $1.3, treasury stock of $304.4 and APIC of $303.1. In October 2016, we retired 13.7 shares of our treasury stock, which resulted in a reduction in common stock of $1.4, treasury stock of $311.0 and APIC of $309.6. In October 2015, we retired 11.3 shares of our treasury stock, which resulted in a reduction in common stock of $1.2, treasury stock of $233.2 and APIC of $232.0. There was no effect on total stockholders' equity as a result of these retirements.

Debt and Credit Agreements Schedule of Long-term Debt Instruments (Tables)

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Schedule of Long-term Debt Instruments [Table Text Block]

A summary of the carrying amounts and fair values of our long-term debt is listed below.



	Effective Interest Rate		December 31,
			2017				2016
			Book Value		Fair Value ¹		Book Value		Fair Value ¹
2.25% Senior Notes due 2017	2.30	%	$	0.0	$	0.0	$	299.4	$	301.4
4.00% Senior Notes due 2022 (less unamortized discount and issuance costs of $1.3 and $1.1, respectively)	4.13	%	247.6		259.0		247.0		258.4
3.75% Senior Notes due 2023 (less unamortized discount and issuance costs of $0.8 and $2.1, respectively)	4.32	%	497.1		513.2		496.6		503.3
4.20% Senior Notes due 2024 (less unamortized discount and issuance costs of $0.7 and $2.6, respectively)	4.24	%	496.7		524.2		496.2		511.6
Other notes payable and capitalized leases			46.2		46.2		65.4		65.4
Total long-term debt			1,287.6				1,604.6
Less: current portion			2.0				323.9
Long-term debt, excluding current portion			$	1,285.6			$	1,280.7


1	See Note 10 for information on the fair value measurement of our long-term debt.

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21475-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e),(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21538-112644

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21506-112644

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28541-108399

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21521-112644

+ Details

Acquisitions Cash Paid for Current and Prior Years' Acquisitions (Tables)

12 Months Ended

Dec. 31, 2017

Business Combinations [Abstract]

Cash Paid For Current And Prior Years' Acquisitions [Table Text Block]

Details of cash paid for current and prior years' acquisitions are listed below.



	Years ended December 31,
	2017			2016			2015
Cost of investment: current-year acquisitions	$	36.8		$	65.7		$	37.8
Cost of investment: prior-year acquisitions	54.6			40.7			53.1
Less: net cash acquired	(7.1		)	(13.6		)	(9.2		)
Total cost of investment	84.3			92.8			81.7
Operating payments¹	47.1			19.1			18.4
Total cash paid for acquisitions ²	$	131.4		$	111.9		$	100.1

Supplementary Data Valuation and Qualifying Accounts - Allowance for Uncollectible Accounts (Tables)

12 Months Ended

Dec. 31, 2017

Valuation and Qualifying Accounts - Allowance for Uncollectible Accounts [Abstract]

Valuation and Qualifying Accounts - Allowance for Uncollectible Accounts Receivable

Valuation and Qualifying Accounts – Allowance for Uncollectible Accounts Receivable



	Years ended December 31,
	2017			2016			2015
Balance at beginning of period	$	55.7		$	54.2		$	59.5
Charges to costs and expenses	9.5			16.7			11.4
Deductions:
Dispositions	(1.0		)	(2.5		)	(2.8		)
Uncollectible accounts written off	(25.5		)	(9.4		)	(9.8		)
Foreign currency translation adjustments	4.0			(3.3		)	(4.1		)
Balance at end of period	$	42.7		$	55.7		$	54.2

Supplementary Data Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2017

Property and Equipment [Abstract]

Property, Plant and Equipment [Table Text Block]

Property and Equipment



	December 31,
	2017			2016
Furniture and equipment	$	634.8		$	604.2
Leasehold improvements	641.5			599.8
Internal-use computer software	331.3			306.5
Land and buildings	79.0			73.1
Gross property and equipment	1,686.6			1,583.6
Less: accumulated depreciation	(1,036.2		)	(961.6		)
Total property and equipment, net	$	650.4		$	622.0

Intangible Assets Changes in Carrying Value of Goodwill (Tables)

12 Months Ended

Dec. 31, 2017

Goodwill and Intangible Assets Disclosure [Abstract]

Changes in Carrying Value of Goodwill

The changes in the carrying value of goodwill for our segments, IAN and CMG, for the years ended December 31, 2017 and 2016 are listed below.



	IAN			CMG			Total ¹
Balance as of December 31, 2015	$	3,051.4		$	557.1		$	3,608.5
Acquisitions	32.7			89.3			122.0
Foreign currency and other	(40.3		)	(15.8		)	(56.1		)
Balance as of December 31, 2016	$	3,043.8		$	630.6		$	3,674.4
Acquisitions	39.6			15.5			55.1
Foreign currency and other	78.4			12.5			90.9
Balance as of December 31, 2017	$	3,161.8		$	658.6		$	3,820.4


1	For all periods presented, no goodwill impairment charge has been recorded.

Intangible Assets Summary of Other Intangible Assets (Tables)

12 Months Ended

Dec. 31, 2017

Summary of Other Intangible Assets [Abstract]

Schedule of Finite-Lived Intangible Assets [Table Text Block]

The following table provides a summary of other intangible assets, which are included in other assets on our Consolidated Balance Sheets.



	December 31,
	2017							2016
	Gross Amount		Accumulated Amortization			Net Amount		Gross Amount		Accumulated Amortization			Net Amount
Customer lists	$	267.3	$	(172.2	)	$	95.1	$	252.4	$	(151.4	)	$	101.0
Trade names	68.8		(33.8		)	35.0		65.5		(28.9		)	36.6
Other	14.4		(3.8		)	10.6		14.3		(3.8		)	10.5
Total	$	350.5	$	(209.8	)	$	140.7	$	332.2	$	(184.1	)	$	148.1

Income Taxes Schedule of Components of Provision for Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]

The provision for income taxes is listed below.



	Years ended December 31,
	2017			2016			2015
U.S. federal income taxes (including foreign withholding taxes):
Current	$	154.1		$	54.3		$	117.8
Deferred	(32.2		)	36.6			46.9
	121.9			90.9			164.7
State and local income taxes:
Current	18.8			8.2			15.1
Deferred	20.4			(1.5		)	13.0
	39.2			6.7			28.1
Foreign income taxes:
Current	107.9			89.8			100.4
Deferred	12.9			10.6			(10.4		)
	120.8			100.4			90.0
Total	$	281.9		$	198.0		$	282.8

Income Taxes Schedule of Effective Income Tax Rate Reconciliation (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]

A reconciliation of the effective income tax rate as reflected in our Consolidated Statements of Operations to the U.S. federal statutory income tax rate is listed below.



	Years ended December 31,
	2017			2016			2015
U.S. federal statutory income tax rate	35.0		%	35.0		%	35.0		%

Income tax provision at U.S. federal statutory rate	$	306.6		$	290.6		$	266.8
State and local income taxes, net of U.S. federal income tax benefit	23.5			4.3			18.3
Impact of foreign operations, including withholding taxes	(6.7		)	(23.9		)	14.7
Change in net valuation allowance ¹	1.4			(13.4		)	(20.6		)
Divestitures	1.1			9.7			11.9
U.S. federal tax credits	(1.7		)	(44.6		)	0.0
Stock compensation	(15.3		)	(9.0		)	0.0
Increase/(decrease) in unrecognized tax benefits	7.0			(22.2		)	(6.5		)
Net impact of the Tax Act	(36.0		)	0.0			0.0
Statutory tax rate changes	0.0			11.4			1.4
Other	2.0			(4.9		)	(3.2		)
Provision for income taxes	$	281.9		$	198.0		$	282.8

Effective income tax rate on operations	32.2		%	23.8		%	37.1		%


1	Reflects changes in valuation allowances that impacted the effective income tax rate for each year presented.

Income Taxes Schedule of Deferred Tax Assets and Liabilities (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule of Deferred Tax Assets and Liabilities [Table Text Block]

The components of deferred tax assets and liabilities are listed below.



	December 31,
	2017			2016
Postretirement/post-employment benefits	$	19.5		$	23.1
Deferred compensation	91.7			192.4
Pension costs	27.6			36.6
Basis differences in fixed assets	(52.0		)	(80.2		)
Rent	27.5			41.7
Interest	45.8			58.9
Accruals and reserves	18.4			17.2
Allowance for doubtful accounts	10.2			13.3
Basis differences in intangible assets	(281.3		)	(405.0		)
Investments in equity securities	(3.3		)	(6.3		)
Tax loss/tax credit carry forwards	357.9			354.6
Prepaid expenses	(1.7		)	(2.9		)
Deferred revenue	(38.2		)	(32.0		)
Other	44.7			44.3
Total deferred tax assets, net	266.8			255.7
Valuation allowance	(243.3		)	(255.6		)
Net deferred tax assets	$	23.5		$	0.1

Accumulated Other Comprehensive Loss, Net of Tax Schedule of Accumulated Other Comprehensive Income (Loss) (Tables)

12 Months Ended

Dec. 31, 2017

Accumulated Other Comprehensive Loss [Abstract]

Schedule of Accumulated Other Comprehensive Income (Loss)

The following table presents the changes in accumulated other comprehensive loss, net of tax, by component.



	Foreign Currency Translation Adjustments			Available-for-Sale Securities			Derivative Instruments			Defined Benefit Pension and Other Postretirement Plans			Total
Balance as of December 31, 2015	$	(665.6	)	$	1.3		$	(9.6	)	$	(171.7	)	$	(845.6	)
Other comprehensive (loss) income before reclassifications	(54.8		)	0.5			0.0			(70.7		)	(125.0		)
Amount reclassified from accumulated other comprehensive loss, net of tax	3.7			(1.2		)	1.2			4.4			8.1
Balance as of December 31, 2016	$	(716.7	)	$	0.6		$	(8.4	)	$	(238.0	)	$	(962.5	)
Other comprehensive income (loss) before reclassifications	130.7			0.0			0.0			(9.7		)	121.0
Amount reclassified from accumulated other comprehensive loss, net of tax	1.1			(0.6		)	1.6			12.0			14.1
Balance as of December 31, 2017	$	(584.9	)	$	0.0		$	(6.8	)	$	(235.7	)	$	(827.4	)

Accumulated Other Comprehensive Loss, Net of Tax Reclassification out of Accumulated Other Comprehensive Income (Tables)

12 Months Ended

Dec. 31, 2017

Accumulated Other Comprehensive Loss [Abstract]

Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]

Amounts reclassified from accumulated other comprehensive loss, net of tax, for the years ended December 31, 2017, 2016 and 2015 are as follows:



	Years ended December 31,									Affected Line Item in the Consolidated Statements of Operations
	2017			2016			2015
Foreign currency translation adjustments ¹	$	1.1		$	3.7		$	23.3		Other expense, net
Gains on available-for-sale securities	(0.7		)	(1.3		)	0.0			Other expense, net
Losses on derivative instruments	2.1			2.0			2.0			Interest expense
Amortization of defined benefit pension and postretirement plans items	13.7			5.8			10.4			Other expense, net
Tax effect	(2.1		)	(2.1		)	(4.2		)	Provision for income taxes
Total amount reclassified from accumulated other comprehensive loss, net of tax	$	14.1		$	8.1		$	31.5


1	These foreign currency translation adjustments are primarily a result of the sales of businesses.

Incentive Compensation Plans Schedule of Stock-based Compensation Expense (Tables)

12 Months Ended

Dec. 31, 2017

Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]

Schedule of Stock-based Compensation Expense

The amounts of stock-based compensation expense as reflected in salaries and related expenses in our Consolidated Statements of Operations, and the related tax benefit, are listed below.



	Years ended December 31,
	2017		2016		2015
Stock options	$	0.0	$	0.2	$	1.0
Stock-settled awards	20.5		16.0		11.6
Cash-settled awards	1.0		0.9		0.7
Performance-based awards	61.5		69.4		57.7
Employee stock purchase plan	1.0		0.7		0.7
Other ¹	0.5		0.8		0.9
Stock-based compensation expense	$	84.5	$	88.0	$	72.6
Tax benefit	$	30.4	$	32.1	$	26.3


1	Represents charges recorded for severance expense related to stock-based compensation awards.

Incentive Compensation Plans Schedule of Stock Options Activity (Tables)

12 Months Ended

Dec. 31, 2017

Summary of Stock Options Assumptions [Abstract]

Share-based Compensation, Stock Options, Activity [Table Text Block]

The following table summarizes our stock option activity during 2017.



	Options		Weighted- Average Exercise Price (per option)		Weighted- Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Stock options outstanding as of January 1, 2017	4.8		$	9.83
Exercised	(1.1	)	11.15
Stock options outstanding as of December 31, 2017	3.7		$	9.44	2.6	$	39.2

Incentive Compensation Plans Stock-based Compensation, Grants in Period Weighted Average (Tables)

12 Months Ended

Dec. 31, 2017

Summary of Stock Options Assumptions [Abstract]

Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value [Table Text Block]

Stock-based compensation awards expected to be settled in cash have been classified as liabilities in our Consolidated Balance Sheets as of December 31, 2017 and 2016.



	Years ended December 31,
	2017		2016		2015
Stock-Settled Awards:
Awards granted	0.8		1.1		0.8
Weighted-average grant-date fair value (per award)	$	24.18	$	21.87	$	22.07
Total fair value of vested awards distributed	$	22.6	$	17.5	$	18.8
Cash-Settled Awards:
Awards granted	0.0		0.1		0.1
Weighted-average grant-date fair value (per award)	$	23.33	$	22.54	$	20.46
Total fair value of vested awards distributed	$	0.9	$	0.7	$	0.2
Performance-Based Awards:
Awards granted	4.8		3.3		2.9
Weighted-average grant-date fair value (per award)	$	20.06	$	19.58	$	20.88
Total fair value of vested awards distributed	$	112.4	$	27.9	$	18.7

Incentive Compensation Plans Schedule of Nonvested Stock Activity (Tables)

12 Months Ended

Dec. 31, 2017

Summary of Stock Options Assumptions [Abstract]

Schedule of Nonvested Share Activity [Table Text Block]



	Stock-Settled Awards					Cash-Settled Awards				Performance-Based Awards
	Awards			Weighted- Average Grant-Date Fair Value (per award)		Awards		Weighted- Average Grant-Date Fair Value (per award)		Awards			Weighted- Average Grant-Date Fair Value (per award)
Non-vested as of January 1, 2017	2.3			$	20.84	0.1		$	20.49	8.5			$	19.16
Granted	0.8			24.18		0.0		23.33		4.8			20.06
Vested	(1.0		)	19.49		0.0		19.27		(4.6		)	16.64
Forfeited	0.0			21.86		0.0		20.50		(0.4		)	20.00
Non-vested as of December 31, 2017	2.1			$	22.78	0.1		$	22.52	8.3			$	21.05
Total unrecognized compensation expense remaining	$	24.1				$	1.0			$	71.9
Weighted-average years expected to be recognized over	1.0					1.0				1.7

Fair Value Measurements Fair Value of Assets and Liabilities Measured on a Recurring Basis (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]



	December 31, 2017								Balance Sheet Classification
	Level 1		Level 2		Level 3		Total		Balance Sheet Classification
Assets
Cash equivalents	$	201.6	$	0.0	$	0.0	$	201.6	Cash and cash equivalents

Liabilities
Contingent acquisition obligations ¹	$	0.0	$	0.0	$	147.0	$	147.0

	December 31, 2016								Balance Sheet Classification
	Level 1		Level 2		Level 3		Total		Balance Sheet Classification
Assets
Cash equivalents	$	440.8	$	0.0	$	0.0	$	440.8	Cash and cash equivalents

Liabilities
Contingent acquisition obligations ¹	$	0.0	$	0.0	$	205.4	$	205.4

Fair Value Measurements Assets and Liabilities Measured at Fair Value on a Nonrecurring (Tables)

12 Months Ended

Dec. 31, 2017

Assets and Liabilities Measured at Fair Value on Recurring Basis [Abstract]

Fair Value Measurements, Nonrecurring [Table Text Block]



	December 31, 2017
	Level 1		Level 2		Level 3		Total
Total long-term debt	$	0.0	$	1,296.4	$	46.2	$	1,342.6

Schedule of Defined Benefit Plans Disclosures (Tables)

12 Months Ended

Dec. 31, 2017

Retirement Benefits [Abstract]

Schedule of Defined Benefit Plans Disclosures



	Domestic Pension Plan						Foreign Pension Plans						Domestic Postretirement Benefit Plan
	Domestic Pension Plan						Foreign Pension Plans						Domestic Postretirement Benefit Plan
Years ended December 31,	2017			2016			2017			2016			2017			2016
Benefit Obligation
Projected benefit obligation as of January 1	$	126.6		$	126.9		$	530.6		$	537.9		$	32.3		$	33.9
Service cost	0.0			0.0			4.9			6.7			0.0			0.0
Interest cost	5.1			5.9			13.5			15.1			1.3			1.5
Benefits paid	(11.4		)	(13.6		)	(19.0		)	(25.7		)	(5.9		)	(5.8		)
Plan participant contributions	0.0			0.0			0.2			0.2			1.6			1.6
Actuarial losses	5.1			7.4			20.3			115.6			2.5			1.1
Settlements and curtailments	0.0			0.0			(19.8		)	(6.3		)	0.0			0.0
Foreign currency effect	0.0			0.0			50.4			(84.2		)	0.0			0.0
Other	0.0			0.0			1.2			(28.7		)	0.0			0.0

Projected benefit obligation as of December 31	$	125.4		$	126.6		$	582.3		$	530.6		$	31.8		$	32.3

Fair Value of Plan Assets
Fair value of plan assets as of January 1	$	95.2		$	101.1		$	365.9		$	399.6		$	0.0		$	0.0
Actual return on plan assets	12.4			7.7			25.1			47.9			0.0			0.0
Employer contributions	2.6			0.0			17.5			23.2			4.3			4.2
Plan participant contributions	0.0			0.0			0.2			0.2			1.6			1.6
Benefits paid	(11.4		)	(13.6		)	(19.0		)	(25.7		)	(5.9		)	(5.8		)
Settlements	0.0			0.0			(19.1		)	(2.2		)	0.0			0.0
Foreign currency effect	0.0			0.0			33.2			(68.6		)	0.0			0.0
Other	0.0			0.0			0.4			(8.5		)	0.0			0.0
																0.0
Fair value of plan assets as of December 31	$	98.8		$	95.2		$	404.2		$	365.9		$	0.0		$	0.0

Funded status of the plans at December 31	$	(26.6	)	$	(31.4	)	$	(178.1	)	$	(164.7	)	$	(31.8	)	$	(32.3	)



	Domestic Pension Plan						Foreign Pension Plans						Domestic Postretirement Benefit Plan
December 31,	2017			2016			2017			2016			2017			2016
Amounts recognized in Consolidated Balance Sheets
Non-current asset	$	0.0		$	0.0		$	9.0		$	7.6		$	0.0		$	0.0
Current liability	0.0			0.0			(6.5		)	(5.5		)	(3.1		)	(3.2		)
Non-current liability	(26.6		)	(31.4		)	(180.6		)	(166.8		)	(28.7		)	(29.1		)

Net liability recognized	$	(26.6	)	$	(31.4	)	$	(178.1	)	$	(164.7	)	$	(31.8	)	$	(32.3	)

Accumulated benefit obligation	$	125.4		$	126.6		$	577.9		$	526.2

Amounts recognized in Accumulated Other Comprehensive Loss, net
Net actuarial loss	$	52.2		$	54.9		$	201.6		$	183.4		$	4.2		$	1.7
Prior service cost (credit)	0.0			0.0			1.1			0.9			(0.4		)	(0.6		)

Total amount recognized	$	52.2		$	54.9		$	202.7		$	184.3		$	3.8		$	1.1



	Domestic Pension Plan				Foreign Pension Plans
December 31,	2017		2016		2017		2016
Pension plans with underfunded or unfunded accumulated benefit obligation
Aggregate projected benefit obligation	$	125.4	$	126.6	$	576.6	$	525.3
Aggregate accumulated benefit obligation	125.4		126.6		575.2		523.8
Aggregate fair value of plan assets	98.8		95.2		389.5		352.9

Employee Benefits Schedule of Net Benefit Costs (Tables)

12 Months Ended

Dec. 31, 2017

Retirement Benefits [Abstract]

Schedule of Net Benefit Costs [Table Text Block]

The components of net periodic benefit cost and key assumptions are listed below.



	Domestic Pension Plan									Foreign Pension Plans									Domestic Postretirement Benefit Plan
Years ended December 31,	2017			2016			2015			2017			2016			2015			2017			2016			2015
Service cost	$	0.0		$	0.0		$	0.0		$	4.9		$	6.7		$	11.1		$	0.0		$	0.0		$	0.0
Interest cost	5.1			5.9			0.3			13.5			15.1			18.9			1.3			1.5			1.5
Expected return on plan assets	(6.2		)	(6.6		)	(7.6		)	(17.7		)	(18.7		)	(20.6		)	0.0			0.0			0.0
Settlement and curtailment losses (gains)	0.0			0.0			0.0			6.8			0.4			(0.2		)	0.0			0.0			0.0
Amortization of:
Prior service cost (credit)	0.0			0.0			0.0			0.1			0.1			0.1			(0.2		)	(0.2		)	(0.1		)
Net actuarial losses	1.5			1.3			6.5			5.5			4.2			4.1			0.0			0.0			0.0
Net periodic cost	$	0.4		$	0.6		$	(0.8	)	$	13.1		$	7.8		$	13.4		$	1.1		$	1.3		$	1.4

Assumptions



	Domestic Pension Plan						Foreign Pension Plans						Domestic Postretirement Benefit Plan
Years ended December 31,	2017		2016		2015		2017		2016		2015		2017		2016		2015

Net periodic cost
Discount rate	4.20	%	4.80	%	4.15	%	2.52	%	3.61	%	3.41	%	4.05	%	4.65	%	4.00	%
Rate of compensation increase	N/A		N/A		N/A		2.36	%	3.18	%	2.99	%	N/A		N/A		N/A
Expected return on plan assets	7.00	%	7.00	%	7.00	%	4.66	%	5.38	%	5.01	%	N/A		N/A		N/A

Benefit obligation
Discount rate	3.70	%	4.20	%	4.80	%	2.36	%	2.52	%	3.61	%	3.65	%	4.05	%	4.65	%
Rate of compensation increase	N/A		N/A		N/A		2.37	%	2.36	%	3.25	%	N/A		N/A		N/A

Health care cost trend rate assumed for next year
Initial rate (weighted-average)													6.50	%	6.75	%	7.00	%
Year ultimate rate is reached													2024		2024		2024
Ultimate rate													5.00	%	5.00	%	5.00	%

Employee Benefits Fair Value of Pension Plan Assets (Tables)

12 Months Ended

Dec. 31, 2017

Retirement Benefits [Abstract]

Fair Value of Pension Plan Assets [Table Text Block]



	December 31, 2017								December 31, 2016
Plan assets subject to fair value hierarchy	Level 1		Level 2		Level 3		Total		Level 1		Level 2		Level 3		Total
Registered investment companies	$	14.7	$	0.0	$	0.0	$	14.7	$	14.4	$	0.0	$	0.0	$	14.4
Limited partnerships	0.0		0.0		29.5		29.5		0.0		0.0		28.0		28.0
Fixed income securities	23.4		0.0		0.0		23.4		22.6		0.3		0.0		22.9
Insurance contracts	0.0		7.9		0.0		7.9		0.0		7.8		0.0		7.8
Other	27.7		0.0		0.0		27.7		20.1		0.0		0.0		20.1
Total plan assets, subject to leveling	$	65.8	$	7.9	$	29.5	$	103.2	$	57.1	$	8.1	$	28.0	$	93.2
Plan assets measured at net asset value
Other investments measured at net asset value ¹							399.8								367.9
Total plan assets							$	503.0							$	461.1


1	Certain investments that are measured at fair value using the net asset value per share (or its equivalent) as a practical expedient have not been classified in the fair value hierarchy but are included to reconcile to the amounts presented in the fair value of plan assets table above.

Employee Benefits Schedule of Allocation of Plan Assets (Tables)

12 Months Ended

Dec. 31, 2017

Retirement Benefits [Abstract]

Schedule of Allocation of Plan Assets [Table Text Block]

As of December 31, 2017, the weighted-average target and actual asset allocations relating to our domestic and foreign pension plans' assets are listed below.



			December 31,
Asset Class	2018 Target Allocation		2017		2016
Alternative investments ¹	27	%	27	%	21	%
Equity securities	23	%	23	%	23	%
Fixed income securities	21	%	21	%	26	%
Liability driven investments ²	14	%	14	%	14	%
Real estate	6	%	6	%	6	%
Other	9	%	9	%	10	%
Total	100	%	100	%	100	%


1	Alternative investments have the flexibility to dynamically invest across a broad range of asset classes including bonds, equity, cash, property and commodities.


2	Liability driven investment strategies use government bonds as well as derivative instruments to hedge a portion of the impact of interest rates and inflation movements on the long-term liabilities.

Segment Information Schedule of Segment Reporting Information, by Segment (Tables)

12 Months Ended

Dec. 31, 2017

Segment Reporting [Abstract]

Schedule of Segment Reporting Information, by Segment

Summarized financial information concerning our reportable segments is shown in the following tables.



	Years ended December 31,
	2017			2016			2015
Revenue:
IAN	$	6,397.3		$	6,319.4		$	6,145.4
CMG	1,485.1			1,527.2			1,468.4
Total	$	7,882.4		$	7,846.6		$	7,613.8

Segment operating income (loss):
IAN	$	907.4		$	898.2		$	850.3
CMG	192.8			190.0			166.3
Corporate and other	(126.6		)	(147.2		)	(141.8		)
Total	973.6			941.0			874.8

Interest expense	(90.8		)	(90.6		)	(85.8		)
Interest income	19.4			20.1			22.8
Other expense, net	(26.2		)	(40.3		)	(49.6		)
Income before income taxes	$	876.0		$	830.2		$	762.2

Depreciation and amortization of property, equipment and intangible assets:
IAN	$	111.8		$	117.7		$	117.5
CMG	20.4			19.5			18.4
Corporate and other	24.9			23.0			21.1
Total	$	157.1		$	160.2		$	157.0

Capital expenditures:
IAN	$	112.0		$	149.2		$	117.5
CMG	17.7			16.6			12.7
Corporate and other	26.2			34.9			30.9
Total	$	155.9		$	200.7		$	161.1

	December 31,
	2017			2016
Total assets:
IAN	$	10,973.0		$	10,660.0
CMG	1,422.9			1,428.3
Corporate and other	299.3			396.9
Total	$	12,695.2		$	12,485.2

Segment Information Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas (Tables)

12 Months Ended

Dec. 31, 2017

Segment Reporting [Abstract]

Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block]

Revenue and long-lived assets, excluding intangible assets, are presented by major geographic area in the following table.



	Revenue						Long-Lived Assets
	Years ended December 31,						December 31,
	2017		2016		2015		2017		2016
Domestic	$	4,714.3	$	4,684.8	$	4,475.5	$	705.5	$	684.8
International:
United Kingdom	681.8		695.7		687.7		56.2		52.0
Continental Europe	716.1		699.8		697.2		73.6		57.0
Asia Pacific	913.6		923.0		916.9		115.5		118.3
Latin America	355.9		372.7		383.5		48.2		49.0
Other	500.7		470.6		453.0		46.1		43.3
Total International	3,168.1		3,161.8		3,138.3		339.6		319.6
Total Consolidated	$	7,882.4	$	7,846.6	$	7,613.8	$	1,045.1	$	1,004.4

Commitments and Contingencies Schedule of Future Minimum Lease Commitments (Tables)

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]



Period	Rent Obligations		Sublease Rental Income			Net Rent
2018	$	335.0	$	(4.2	)	$	330.8
2019	312.1		(3.8		)	308.3
2020	285.3		(2.5		)	282.8
2021	251.4		(1.4		)	250.0
2022	204.1		(0.8		)	203.3
Thereafter	727.2		(0.5		)	726.7
Total	$	2,115.1	$	(13.2	)	$	2,101.9

Commitments and Contingencies Schedule of Contingent Acquisition Obligations (Tables)

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Schedule of Business Acquisitions by Acquisition, Contingent Consideration [Table Text Block]

The following table details the estimated future contingent acquisition obligations payable in cash as of December 31, 2017.



	2018		2019		2020		2021		2022		Thereafter		Total
Deferred acquisition payments	$	41.9	$	27.5	$	16.1	$	24.4	$	4.8	$	6.3	$	121.0
Redeemable noncontrolling interests and call options with affiliates ¹	37.1		26.4		62.9		10.3		6.6		4.1		147.4
Total contingent acquisition payments	$	79.0	$	53.9	$	79.0	$	34.7	$	11.4	$	10.4	$	268.4

Results by Quarter (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Financial Information

Results by Quarter (Unaudited)



	Three Months Ended March 31,						Three Months Ended June 30,						Three Months Ended September 30,						Three Months Ended December 31,
	2017			2016			2017			2016			2017			2016			2017			2016
Revenue	$	1,753.9		$	1,742.0		$	1,884.9		$	1,917.9		$	1,902.6		$	1,922.2		$	2,341.0		$	2,264.5
Salaries and related expenses ¹	1,275.4			1,268.8			1,239.3			1,229.5			1,227.6			1,228.0			1,325.8			1,308.8
Office and general expenses	448.8			450.2			439.1			464.1			455.9			486.2			496.9			470.0
Operating income	29.7			23.0			206.5			224.3			219.1			208.0			518.3			485.7
Other income (expense), net ^1,2	0.8			(19.2		)	(15.4		)	0.4			(9.9		)	5.3			(1.7		)	(26.8		)
Total (expenses) and other income	(14.9		)	(36.0		)	(36.4		)	(18.5		)	(26.8		)	(11.7		)	(19.5		)	(44.6		)
(Benefit of) provision for income taxes ³	(2.1		)	(15.6		)	75.4			43.7			42.5			63.8			166.1			106.1
Net income	18.1			2.7			94.6			160.2			148.8			132.7			333.5			336.9
Net income available to IPG common stockholders	$	21.5		$	5.4		$	94.7		$	156.9		$	146.2		$	128.6		$	316.6		$	317.6

Earnings per share available to IPG common stockholders:
Basic	$	0.05		$	0.01		$	0.24		$	0.39		$	0.38		$	0.32		$	0.82		$	0.81
Diluted	$	0.05		$	0.01		$	0.24		$	0.38		$	0.37		$	0.32		$	0.81		$	0.78

Dividends declared per common share	$	0.18		$	0.15		$	0.18		$	0.15		$	0.18		$	0.15		$	0.18		$	0.15


1	As part of the adoption of FASB ASU 2017-07, we have reclassified a portion of postretirement costs from salaries and related expenses to other income (expense), net.


2	The three months ended June 30 and September 30, 2017 included pre-tax net losses of $13.1 and $8.7, respectively, on sales of businesses. The three months ended March 31 and December 31, 2016 included pre-tax net losses of $16.3 and $25.3, respectively, on sales of businesses.

^[1]

[1]	As part of the adoption of FASB ASU 2017-07, we have reclassified a portion of postretirement costs from salaries and related expenses to other income (expense), net.

Summary of Significant Accounting Policies (Details) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares
Retirement of treasury stock, amount	$ 0.0	$ 0.0	$ 0.0
ERP Systems, Useful Life	10
Selling, general and administrative expense	$ 118.6	138.8
Depreciation and amortization	$ 157.1	160.2	157.0
Leasehold Improvements, Useful Life	the shorter of the useful life or the remaining lease term
Number of Reporting Units for Purposes of Annual Goodwill Impairment Test	11
Foreign Currency Transaction pre-tax Gain (Loss)	$ 1.9	$ 2.1	$ 2.0
Minimum
Furniture and Equipment, Useful Life	3 years
Buildings, Useful Life	10 years
Other Internal Use Software, Useful Life	3
Finite-Lived Intangible Assets, Useful Life	7 years
Maximum
Furniture and Equipment, Useful Life	7 years
Buildings, Useful Life	35 years
Other Internal Use Software, Useful Life	7
Finite-Lived Intangible Assets, Useful Life	15 years
Common Stock [Member]
Retirement of treasury stock, shares \| shares	(13.4)	(13.7)	(11.3)
Retirement of treasury stock, amount	$ (1.3)	$ (1.4)	$ (1.2)
Treasury Stock [Member]
Retirement of treasury stock, amount	304.4	311.0	233.2
Additional Paid-in Capital [Member]
Retirement of treasury stock, amount	$ (303.1)	$ (309.6)	$ (232.0)

Debt and Credit Agreements Long-Term Debt (Details) - USD ($)
$ in Millions

12 Months Ended

Dec. 31, 2017

Dec. 31, 2016

Debt Instrument [Line Items]

Long-term debt, gross

$ 1,287.6

$ 1,604.6

Long-term debt, current maturities

2.0

323.9

Long-term debt, excluding current maturities

1,285.6

1,280.7

Deb instrument, unamortized debt issuance costs

13.0

12.3

Long-term debt, fair value

1,342.6

2.25% Notes

Debt Instrument [Line Items]

Debt instrument, face amount

300.0

Long-term debt, gross

0.0

299.4

Debt instrument, unamortized discount

0.0

Deb instrument, unamortized debt issuance costs

0.0

Long-term debt, fair value

^[1]

$ 0.0

301.4

Debt instrument, maturity date

Nov. 15, 2017

Interest rate, stated percentage

2.25%

Debt instrument, interest rate, effective percentage

2.30%

Total cash paid to redeem 2.25% Note

$ 303.4

Accrued and unpaid interest

3.4

4.00% Notes

Debt Instrument [Line Items]

Debt instrument, face amount

250.0

Long-term debt, gross

247.6

247.0

Debt instrument, unamortized discount

1.3

Deb instrument, unamortized debt issuance costs

1.1

Long-term debt, fair value

^[1]

$ 259.0

258.4

Debt instrument, maturity date

Mar. 15, 2022

Interest rate, stated percentage

4.00%

Debt instrument, interest rate, effective percentage

4.13%

3.75% Notes

Debt Instrument [Line Items]

Debt instrument, face amount

$ 500.0

Long-term debt, gross

497.1

496.6

Debt instrument, unamortized discount

0.8

Deb instrument, unamortized debt issuance costs

2.1

Long-term debt, fair value

^[1]

$ 513.2

503.3

Debt instrument, maturity date

Feb. 15, 2023

Interest rate, stated percentage

3.75%

Debt instrument, interest rate, effective percentage

4.32%

4.20% Notes

Debt Instrument [Line Items]

Debt instrument, face amount

$ 500.0

Long-term debt, gross

496.7

496.2

Debt instrument, unamortized discount

0.7

Deb instrument, unamortized debt issuance costs

2.6

Long-term debt, fair value

^[1]

$ 524.2

511.6

Debt instrument, maturity date

Apr. 15, 2024

Interest rate, stated percentage

4.20%

Debt instrument, interest rate, effective percentage

4.24%

Notes Payable, Other Payables [Member]

Debt Instrument [Line Items]

Long-term debt, gross

$ 46.2

65.4

Long-term debt, fair value

^[1]

$ 46.2

$ 65.4

[1]	See Note 10 for information on the fair value measurement of our long-term debt.

Debt and Credit Agreements Annual Maturities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
Long-term debt, maturities, repayments of principal in next twelve months	$ 2.0
Long-term debt, maturities, repayments of principal in year two	3.1
Long-term debt, maturities,repayments of principal in year three	1.0
Long-term debt, maturities, repayments of principal in year four	0.0
Long-term debt, maturities, repayments of principal in year five	247.6
Long-term debt, maturities, repayments of principal after year five	1,033.9
Total long-term debt	$ 1,287.6	$ 1,604.6

Debt and Credit Agreements Credit Agreements (Details) - USD ($)
$ in Millions

12 Months Ended

Dec. 31, 2017

Dec. 31, 2016

Sep. 30, 2017

Line of Credit Facility [Line Items]

Margin for base rate advances

0.10%

Margin for Eurocurrency rate advances

1.10%

Annual rate for fronting fees accrued on letters of credit

0.25%

Annual facility fee

0.15%

Interest coverage ratio minimum

^[1]

5.00x

Leverage ratio maximum

^[2]

3.50x

Committed credit facility [Member]

Line of Credit Facility [Line Items]

Line of credit facility, maximum borrowing capacity

$ 1,500.0

$ 1,000.0

Line of credit facility, available capacity increase amount

$ 250.0

Line of credit facility, expiration date

Oct. 25, 2022

Limits on letters of credit

$ 50.0

Line of credit facility, amount outstanding

0.0

Letters of credit, amount outstanding

8.4

$ 4.9

Line of credit facility, remaining borrowing capacity

1,491.6

995.1

Uncommitted credit facility

Line of Credit Facility [Line Items]

Line of credit facility, amount outstanding

84.9

85.7

Line of credit facility, current borrowing capacity

926.2

856.6

Line of credit facility, average outstanding amount

$ 223.8

$ 216.0

Line of credit facility, weighted average interest rate, over time

2.90%

[1]

The interest coverage ratio is defined as EBITDA, as defined in the Credit Agreement, to net interest expense for the four quarters then ended.

[2]

Debt and Credit Agreements Commercial Paper (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017
Debt Disclosure [Abstract]
Commercial paper, current borrowing capacity	$ 1,500.0	$ 1,000.0
Commercial paper, amount outstanding	0.0
Commercial paper, average outstanding amount	$ 477.4
Commercial paper, weighted average interest rate, over time	1.50%
Commercial paper, weighted-average maturity days outstanding, over time	17

Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income available to IPG common stockholders									$ 579.0	$ 608.5	$ 454.6
Weighted-average number of common shares outstanding - basic									389.6	397.9	408.1
Restricted stock, stock options and other equity awards									7.7	10.1	7.6
Weighted-average number of common shares outstanding - diluted									397.3	408.0	415.7
Basic	$ 0.82	$ 0.38	$ 0.24	$ 0.05	$ 0.81	$ 0.32	$ 0.39	$ 0.01	$ 1.49	$ 1.53	$ 1.11
Diluted	$ 0.81	$ 0.37	$ 0.24	$ 0.05	$ 0.78	$ 0.32	$ 0.38	$ 0.01	$ 1.46	$ 1.49	$ 1.09

Acquisitions Narrative (Details) $ in Millions	12 Months Ended
Acquisitions Narrative (Details) $ in Millions	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Goodwill and intangible assets related to acquisitions	$ 62.0	$ 149.0	$ 61.0
Number of businesses acquired	10	10	5
IAN
Number of businesses acquired	8	3	4
CMG
Number of businesses acquired	2	7	1

Acquisitions Cash Paid for Acquisitions (Details) - USD ($)
$ in Millions

12 Months Ended

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Cash Paid for Acquisitions [Abstract]

Cost of investment: current-year acquisitions

$ 36.8

$ 65.7

$ 37.8

Cost of investment: prior-year acquisitions

54.6

40.7

53.1

Less: net cash acquired

(7.1)

(13.6)

(9.2)

Total cost of investment

84.3

92.8

81.7

Operating payments

^[1]

47.1

19.1

18.4

Total cash paid for acquisitions

^[2]

131.4

111.9

100.1

Acquisitions, net of cash acquired, investing cash flows

30.6

52.0

28.6

Payments for previous acquisition, financing cash flows

$ 53.7

$ 40.8

$ 53.1

[1]

[2]

Redeemable Noncontrolling Interests (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Redeemable Noncontrolling Interests
Balance at beginning of period	$ 252.8	$ 251.9	$ 257.4
Change in related noncontrolling interest balance	(2.8)	4.9	0.8
Changes in redemption value of redeemable noncontrolling interests:
Additions	7.7	6.8	16.5
Redemptions and other	(18.5)	(14.8)	(25.1)
Redemption value adjustments	12.9	4.0	2.3
Balance at end of period	$ 252.1	$ 252.8	$ 251.9

Valuation and Qualifying Accounts - Allowance for Uncollectible Accounts Receivable (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 55.7	$ 54.2	$ 59.5
Charges to costs and expenses	9.5	16.7	11.4
Deductions:
Dispositions	(1.0)	(2.5)	(2.8)
Uncollectible accounts written off	(25.5)	(9.4)	(9.8)
Foreign currency translation adjustment	4.0	(3.3)	(4.1)
Balance at end of period	$ 42.7	$ 55.7	$ 54.2

Supplementary Data Property and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Furniture and equipment	$ 634.8	$ 604.2
Leasehold improvements	641.5	599.8
Internal-use computer software	331.3	306.5
Land and buildings	79.0	73.1
Total property and equipment, gross	1,686.6	1,583.6
Less: accumulated depreciation	(1,036.2)	(961.6)
Total property and equipment, net	650.4	622.0
Depreciation and amortization expense for property and equipment	$ 135.9	$ 138.3	$ 130.9

Accrued Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Accrued Liabilities [Abstract]
Salaries, benefits and related expenses	$ 441.7	$ 499.0
Office and related expenses	53.2	46.7
Acquisition obligations	42.0	77.5
Interest	16.4	17.3
Other	121.4	153.5
Total accrued liabilities	$ 674.7	$ 794.0

Other Expense, Net (Details) - USD ($)
$ in Millions

3 Months Ended

12 Months Ended

Dec. 31, 2017

^[1],[2]

Sep. 30, 2017

^[1],[2]

Jun. 30, 2017

^[1],[2]

Mar. 31, 2017

^[1],[2]

Dec. 31, 2016

^[1],[2]

Sep. 30, 2016

^[1],[2]

Jun. 30, 2016

^[1],[2]

Mar. 31, 2016

^[1],[2]

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Other Nonoperating Income (Expense) [Abstract]

Net losses on sales of businesses

$ (24.1)

$ (41.4)

$ (50.0)

Other

(2.1)

1.1

0.4

Total other expense, net

$ (1.7)

$ (9.9)

$ (15.4)

$ 0.8

$ (26.8)

$ 5.3

$ 0.4

$ (19.2)

$ (26.2)

$ (40.3)

$ (49.6)

[1]	As part of the adoption of FASB ASU 2017-07, we have reclassified a portion of postretirement costs from salaries and related expenses to other income (expense), net.
[2]	The three months ended June 30 and September 30, 2017 included pre-tax net losses of $13.1 and $8.7, respectively, on sales of businesses. The three months ended March 31 and December 31, 2016 included pre-tax net losses of $16.3 and $25.3, respectively, on sales of businesses.

Share Repurchase Program (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of shares repurchased	13.7	13.3	13.6
Aggregate cost, including fees	$ 300.1	$ 303.3	$ 285.2
Average price per share, including fees	$ 21.97	$ 22.76	$ 20.97
2017 Share Repurchase Program
Share repurchase program, initial authorized amount	$ 300.0
Stock repurchase program, remaining authorized repurchase amount	$ 155.5

Supplemental Cash Flow Information (Details) - USD ($)
$ in Millions

12 Months Ended

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Supplemental Cash Flow Information [Abstract]

Cash paid for interest

$ 82.3

$ 78.8

$ 74.5

Cash paid for income taxes, net of refunds

^[1]

228.4

244.1

231.9

Tax refunds

$ 31.9

$ 26.6

$ 13.0

[1]	Refunds of $31.9, $26.6 and $13.0 were received for the years ended December 31, 2017, 2016 and 2015, respectively.

Goodwill (Details) - USD ($)
$ in Millions

12 Months Ended

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Goodwill

Goodwill

$ 3,820.4

$ 3,674.4

$ 3,608.5

^[1]

Current year acquisitions

55.1

122.0

Foreign currency and other

90.9

(56.1)

IAN

Goodwill

Goodwill

^[1]

3,161.8

3,043.8

3,051.4

Current year acquisitions

39.6

32.7

Foreign currency and other

78.4

(40.3)

CMG

Goodwill

Goodwill

^[1]

658.6

630.6

$ 557.1

Current year acquisitions

15.5

89.3

Foreign currency and other

$ 12.5

$ (15.8)

[1]	For all periods presented, no goodwill impairment charge has been recorded.

Other Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
Other Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Future amortization expense 2018	$ 23.3
Future amortization expense 2019	22.1
Future amortization expense 2020	20.4
Future amortization expense 2021	19.3
Future amortization expense 2022	16.4
Finite-Lived Intangible Assets [Line Items]
Amortization expense of intangible assets	21.2	$ 21.9	$ 26.1
Acquired finite-lived intangible assets related to acquisitions	7.0	29.0
Gross Amount	350.5	332.2
Accumulated Amortization	(209.8)	(184.1)
Net Amount	140.7	148.1
Customer lists
Finite-Lived Intangible Assets [Line Items]
Gross Amount	267.3	252.4
Accumulated Amortization	(172.2)	(151.4)
Net Amount	95.1	101.0
Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Amount	68.8	65.5
Accumulated Amortization	(33.8)	(28.9)
Net Amount	35.0	36.6
Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross Amount	14.4	14.3
Accumulated Amortization	(3.8)	(3.8)
Net Amount	$ 10.6	$ 10.5
Minimum
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, useful life	7 years
Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, useful life	15 years

Income Taxes The 2017 U.S. Tax Cuts and Jobs Act (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Foreign tax credits	$ 31.2
Provisional deferred income tax benefit due to the Tax Act		$ 104.7
Provisional tax effect of this deemed repatriation of unremitted foreign earnings		$ 62.3

Components of Income Before Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income before income taxes, Domestic	$ 528.2	$ 504.7	$ 461.0
Income before income taxes, Foreign	347.8	325.5	301.2
Income before income taxes	$ 876.0	$ 830.2	$ 762.2

Provision for Income Taxes (Details) - USD ($)
$ in Millions

3 Months Ended

12 Months Ended

Dec. 31, 2017

^[1]

Sep. 30, 2017

^[1]

Jun. 30, 2017

^[1]

Mar. 31, 2017

^[1]

Dec. 31, 2016

^[1]

Sep. 30, 2016

^[1]

Jun. 30, 2016

^[1]

Mar. 31, 2016

^[1]

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

U.S. federal income taxes (including foreign withholding taxes):

Current federal income taxes

$ 154.1

$ 54.3

$ 117.8

Deferred federal income taxes

(32.2)

36.6

46.9

Total federal income taxes

121.9

90.9

164.7

State and local income taxes:

Current state and local income taxes

18.8

8.2

15.1

Deferred state and local income taxes

20.4

(1.5)

13.0

Total state and local income taxes

39.2

6.7

28.1

Foreign income taxes:

Current foreign income taxes

107.9

89.8

100.4

Deferred foreign income taxes

12.9

10.6

(10.4)

Total foreign income taxes

120.8

100.4

90.0

Total provision for income taxes

$ 166.1

$ 42.5

$ 75.4

$ (2.1)

$ 106.1

$ 63.8

$ 43.7

$ (15.6)

$ 281.9

$ 198.0

$ 282.8

[1]

Reconciliation of Effective Income Tax Rate (Details) - USD ($)
$ in Millions

3 Months Ended

12 Months Ended

Dec. 31, 2017

^[2]

Sep. 30, 2017

^[2]

Jun. 30, 2017

^[2]

Mar. 31, 2017

^[2]

Dec. 31, 2016

^[2]

Sep. 30, 2016

^[2]

Jun. 30, 2016

^[2]

Mar. 31, 2016

^[2]

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Valuation Allowance [Line Items]

U.S. federal statutory income tax rate

35.00%

Income tax provision at U.S. federal statutory rate

$ 306.6

$ 290.6

$ 266.8

State and local income taxes, net of federal income tax benefit

23.5

4.3

18.3

Impact of foreign operations, including withholding taxes

(6.7)

(23.9)

14.7

Change in net valuation allowance

^[1]

1.4

(13.4)

(20.6)

Divestitures

1.1

9.7

11.9

U.S. federal tax credits

(1.7)

(44.6)

0.0

Stock Compensation

(15.3)

(9.0)

0.0

Increase (decrease) in unrecognized tax benefits

7.0

(22.2)

(6.5)

Net impact of the Tax Act

(36.0)

0.0

Statutory tax rate changes

0.0

11.4

1.4

Other

2.0

(4.9)

(3.2)

Total provision for income taxes

$ 166.1

$ 42.5

$ 75.4

$ (2.1)

$ 106.1

$ 63.8

$ 43.7

$ (15.6)

$ 281.9

$ 198.0

$ 282.8

Effective income tax rate on operations

32.20%

23.80%

37.10%

[1]

Reflects changes in valuation allowances that impacted the effective income tax rate for each year presented.

[2]

Income Taxes Primary Impact on Provision for Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Net impact of the Tax Act	$ 36.0	$ 0.0	$ 0.0
Tax credits	$ 1.7	44.6	$ 0.0
Previously unrecognized tax benefits		23.4
Reversal of valuation allowance		$ 12.2

Components of Deferred Tax Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred Tax Assets, Net [Abstract]
Postretirement/post-employment benefits	$ 19.5	$ 23.1
Deferred compensation	91.7	192.4
Pension costs	27.6	36.6
Basis differences in fixed assets	(52.0)	(80.2)
Rent	27.5	41.7
Interest	45.8	58.9
Accruals and reserves	18.4	17.2
Allowance for doubtful accounts	10.2	13.3
Basis differences in intangible assets	(281.3)	(405.0)
Investments in equity securities	(3.3)	(6.3)
Tax loss/tax credit carry forwards	357.9	354.6
Prepaid expenses	(1.7)	(2.9)
Deferred revenue	(38.2)	(32.0)
Other	44.7	44.3
Total deferred tax assets, net	266.8	255.7
Valuation allowance	(243.3)	(255.6)	$ (275.1)	$ (332.2)
Net deferred tax assets	$ 23.5	$ 0.1

Income Taxes Change in Valuation Allowances (Details) - USD ($)
$ in Millions

12 Months Ended

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Summary of Valuation Allowances

Beginning balance

$ 255.6

$ 275.1

$ 332.2

Reversed to costs and expenses

(4.6)

(15.4)

(20.8)

(Reversed) charged to gross tax assets and other accounts 1

^[1]

(27.0)

9.5

(9.2)

Foreign currency translation

19.3

(13.6)

(27.1)

Ending balance

243.3

255.6

$ 275.1

Deferred Tax Assets, Operating Loss Carryforwards, Components [Abstract]

Operating Loss Carryforwards

1,186.8

Deferred Tax Liabilities, Undistributed Foreign Earnings

2,774.8

$ 2,622.4

Foreign Tax Authority

Deferred Tax Assets, Operating Loss Carryforwards, Components [Abstract]

Deferred Tax Assets, Operating Loss Carryforwards, Not Subject to Expiration

656.6

Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration

530.2

State and Local Jurisdiction [Member]

Deferred Tax Assets, Operating Loss Carryforwards, Components [Abstract]

Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration

$ 45.0

Minimum | Foreign Tax Authority

Deferred Tax Assets, Operating Loss Carryforwards, Components [Abstract]

Operating Loss Carryforwards, Expiration Date

Jan. 01, 2018

Minimum | State and Local Jurisdiction [Member]

Deferred Tax Assets, Operating Loss Carryforwards, Components [Abstract]

Operating Loss Carryforwards, Expiration Date

Jan. 01, 2018

Maximum | Foreign Tax Authority

Deferred Tax Assets, Operating Loss Carryforwards, Components [Abstract]

Operating Loss Carryforwards, Expiration Date

Jan. 01, 2037

Maximum | State and Local Jurisdiction [Member]

Deferred Tax Assets, Operating Loss Carryforwards, Components [Abstract]

Operating Loss Carryforwards, Expiration Date

Jan. 01, 2037

[1]	Primarily represents changes to the valuation allowance related to the change of a corresponding deferred tax asset.

Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued [Abstract]
Balance at beginning of period	$ 246.7	$ 226.9	$ 238.0
Increases as a result of tax positions taken during a prior year	6.3	65.0	5.2
Decreases as a result of tax positions taken during a prior year	(8.1)	(47.5)	(19.7)
Settlements with taxing authorities	(0.8)	(4.6)	(4.1)
Lapse of statutes of limitation	(3.3)	(11.8)	(3.8)
Increases as a result of tax positions taken during the current year	31.1	18.7	11.3
Balance at end of period	271.9	246.7	$ 226.9
Income Tax Contingency [Line Items]
Unrecognized tax benefits that would impact effective tax rate	249.2
Income tax penalties and interest accrued	27.9	20.9
Income tax penalties and interest expense	7.0	$ 0.7
Minimum [Member]
Income Tax Contingency [Line Items]
Anticipated decrease in unrecognized tax benefits	28.0
Maximum [Member]
Income Tax Contingency [Line Items]
Anticipated decrease in unrecognized tax benefits	$ 38.0

Accumulated Other Comprehensive Loss, Net of Tax Changes in AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Available-for-sale securities, before reclassifications	$ 0.0	$ 0.5	$ 0.5
Total other comprehensive income, before reclassifications	121.0	(125.0)
Total reclassification from AOCI	14.1	8.1	31.5
Accumulated Other Comprehensive Income (Loss), net of tax	(827.4)	(962.5)	(845.6)
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Foreign currency translation adjustment, before reclassifications	130.7	(54.8)
Foreign currency translation adjustment, amount reclassified from AOCI, net of tax	1.1	3.7
Foreign currency translation adjustment, net of tax	(584.9)	(716.7)	(665.6)
Available-for-sale Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Available-for-sale securities, before reclassifications	0.0	0.5
Available-for-sale securities, amount reclassified from AOCI, net of tax	(0.6)	(1.2)
Available-for-sale securities adjustment, net of tax	0.0	0.6	1.3
Derivative Instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Derivative instruments, before reclassifications	0.0	0.0
Derivative instruments, amount reclassified from AOCI, net of tax	1.6	1.2
Derivative Instruments, net of tax	(6.8)	(8.4)	(9.6)
Defined Benefit and Postretirement Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined Benefit and Postretirement Plans, before reclassifications	(9.7)	(70.7)
Defined benefit and Postretirement Plans, amount reclassified from AOCI, net of tax	12.0	4.4
Pension and Other Postretirement Benefit Plans, net of tax	$ (235.7)	$ (238.0)	$ (171.7)

Accumulated Other Comprehensive Loss, Net of Tax Reclassifications from AOCI, net of tax (Details) - USD ($)
$ in Millions

12 Months Ended

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]

Total income tax effect

$ (2.1)

$ (4.2)

Total reclassified from AOCI, net of tax

14.1

8.1

31.5

Foreign Currency Translation Adjustment

Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]

Reclassification from AOCI, before tax

^[1]

1.1

3.7

23.3

Available-for-sale Securities

Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]

Reclassification from AOCI, before tax

(0.7)

(1.3)

0.0

Derivative Instruments

Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]

Reclassification from AOCI, before tax

2.1

2.0

Defined Benefit and Postretirement Plans

Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]

Reclassification from AOCI, before tax

$ 13.7

$ 5.8

$ 10.4

[1]	These foreign currency translation adjustments are primarily a result of the sales of businesses.

Plan Information (Details) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) shares
Incentive compensation plan initiation year	2014
Number of shares initially available for grant	28.8
Maximum shares participants are eligible to receive	2.0
Maximum cash award per employee \| $	$ 10.0
Number of years stock options expire from grant date	10 years
Vesting period in which the fair value of shares on grant date is amortized over, years	3 years
Minimum [Member]
Stock options exercisable period	2 years
Maximum [Member]
Stock options exercisable period	4 years

Stock Based Compensation Expense (Details) - USD ($)
$ in Millions

12 Months Ended

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Stock-based Payment Award

Stock-based compensation expense

$ 84.5

$ 88.0

$ 72.6

Tax benefit

30.4

32.1

26.3

Employee Stock Option

Stock-based Payment Award

Stock-based compensation expense

0.0

0.2

1.0

Stock-settled awards

Stock-based Payment Award

Stock-based compensation expense

20.5

16.0

11.6

Cash-settled awards

Stock-based Payment Award

Stock-based compensation expense

1.0

0.9

0.7

Performance-based awards

Stock-based Payment Award

Stock-based compensation expense

61.5

69.4

57.7

Employee stock purchase plan

Stock-based Payment Award

Stock-based compensation expense

1.0

0.7

Other

Stock-based Payment Award

Stock-based compensation expense

^[1]

$ 0.5

$ 0.8

$ 0.9

[1]	Represents charges recorded for severance expense related to stock-based compensation awards.

Incentive Compensation Plans Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock-based Payment Award
Intrinsic value of stock options exercised	$ 15.1	$ 15.2	$ 16.1
Proceeds from stock options exercised including taxes withheld	$ 20.0	$ 18.2	$ 20.4
Employee Stock Option
Stock-based Payment Award
Stock options outstanding as of January 1, 2017	4.8
Stock options outstanding as of Jan 1, 2017, Weighted-average exercise price	$ 9.83
Exercised	(1.1)	(1.2)	(1.4)
Exercised, weighted-average exercise price	$ 11.15
Stock options outstanding as of December 31, 2017	3.7	4.8
Stock options outstanding as of Dec 31, 2017, Weighted-average exercise price	$ 9.44	$ 9.83
Options outstanding, weighted average remaining contractual term	2 years 7 months
Stock options outstanding, aggregate intrinsic value	$ 39.2

Share-based Compensation Awards (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock-settled awards
Stock-based Payment Award
Awards granted	0.8	1.1	0.8
Weighted-average grant-date fair value (per award)	$ 24.18	$ 21.87	$ 22.07
Total fair value of vested awards distributed	$ 22.6	$ 17.5	$ 18.8
Accrued dividends on non-vested stock-settled awards	1.5	1.3
Dividends paid for stock-settled awards	$ 1.2	$ 0.6
Cash-settled awards
Stock-based Payment Award
Awards granted	0.0	0.1	0.1
Weighted-average grant-date fair value (per award)	$ 23.33	$ 22.54	$ 20.46
Total fair value of vested awards distributed	$ 0.9	$ 0.7	$ 0.2
Performance-based awards
Stock-based Payment Award
Awards granted	4.8	3.3	2.9
Weighted-average grant-date fair value (per award)	$ 20.06	$ 19.58	$ 20.88
Total fair value of vested awards distributed	$ 112.4	$ 27.9	$ 18.7

Non-vested Award Activity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock-settled awards
Stock-based Payment Award
Non-vested as of January 1, 2017	2.3
Nonvested as of January 1, 2017, weighted-average grant date fair value	$ 20.84
Granted	0.8
Granted, Weighted-average grant-date fair value	$ 24.18	$ 21.87	$ 22.07
Vested	(1.0)
Vested, Weighted-average grant date fair value	$ 19.49
Forfeited	0.0
Forfeited, Weighted-average grant date fair value	$ 21.86
Non-vested as of December 31, 2017	2.1	2.3
Nonvested as of December 31, 2017, weighted-average grant date fair value	$ 22.78	$ 20.84
Total unrecognized compensation expense remaining	$ 24.1
Weighted-average years expected to be recognized over	1 year
Cash-settled awards
Stock-based Payment Award
Non-vested as of January 1, 2017	0.1
Nonvested as of January 1, 2017, weighted-average grant date fair value	$ 20.49
Granted	0.0
Granted, Weighted-average grant-date fair value	$ 23.33	$ 22.54	$ 20.46
Vested	0.0
Vested, Weighted-average grant date fair value	$ 19.27
Forfeited	0.0
Forfeited, Weighted-average grant date fair value	$ 20.50
Non-vested as of December 31, 2017	0.1	0.1
Nonvested as of December 31, 2017, weighted-average grant date fair value	$ 22.52	$ 20.49
Total unrecognized compensation expense remaining	$ 1.0
Weighted-average years expected to be recognized over	1 year
Cash awards granted during the period target value	$ 2.8	$ 5.2	$ 1.3
Incentive compensation expense, non share-based	$ 2.5	$ 3.1	$ 3.0
Performance-based awards
Stock-based Payment Award
Non-vested as of January 1, 2017	8.5
Nonvested as of January 1, 2017, weighted-average grant date fair value	$ 19.16
Granted	4.8
Granted, Weighted-average grant-date fair value	$ 20.06	$ 19.58	$ 20.88
Vested	(4.6)
Vested, Weighted-average grant date fair value	$ 16.64
Forfeited	(0.4)
Forfeited, Weighted-average grant date fair value	$ 20.00
Non-vested as of December 31, 2017	8.3	8.5
Nonvested as of December 31, 2017, weighted-average grant date fair value	$ 21.05	$ 19.16
Total unrecognized compensation expense remaining	$ 71.9
Weighted-average years expected to be recognized over	1 year 8 months
Cash awards granted during the period target value	$ 38.4	$ 37.4	$ 31.8
Incentive compensation expense, non share-based	$ 35.3	$ 39.8	$ 35.8

Incentive Compensation Plans Employee Stock Purchase Plans (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2015
Employee Stock Ownership Plan (ESOP), Shares in ESOP [Abstract]
Maximum employee subscription rate	10.00%
Maximum number of shares per employee	900
Employee stock purchase plan description	90% of the lesser of the average market price of a share on the first business day of the offering period or the average market price of a share on the last business day of the offering period of three months
Employee Stock Purchase Plan, stock issued, shares	500,000	3,000,000
Employee Stock Purchase Plan, stock reserved for issuance, shares	10,000,000

Fair Value on a Recurring Basis (Details) - USD ($)
$ in Millions

12 Months Ended

Dec. 31, 2017

Dec. 31, 2016

Fair value assets and liabilities measured on recurring basis

Cash equivalents

$ 201.6

$ 440.8

Contingent acquisition obligations

^[1]

147.0

205.4

Contingent acquisition obligation, total change

(58.4)

Contingent acquisition obligation, payments

(105.3)

Contingent acquisition obligation, additions

40.8

Level 1

Fair value assets and liabilities measured on recurring basis

Cash equivalents

201.6

440.8

Contingent acquisition obligations

^[1]

0.0

Level 2

Fair value assets and liabilities measured on recurring basis

Cash equivalents

0.0

Contingent acquisition obligations

^[1]

0.0

Level 3

Fair value assets and liabilities measured on recurring basis

Cash equivalents

0.0

Contingent acquisition obligations

^[1]

$ 147.0

$ 205.4

[1]

Fair Value on a Nonrecurring Basis (Details) $ in Millions	Dec. 31, 2017 USD ($)
Fair value assets and liabilities measured on nonrecurring basis
Long-term debt, fair value	$ 1,342.6
Level 1
Fair value assets and liabilities measured on nonrecurring basis
Long-term debt, fair value	0.0
Level 2
Fair value assets and liabilities measured on nonrecurring basis
Long-term debt, fair value	1,296.4
Level 3
Fair value assets and liabilities measured on nonrecurring basis
Long-term debt, fair value	$ 46.2

Employee Benefits (Details) $ in Millions	12 Months Ended
Employee Benefits (Details) $ in Millions	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Retirement Benefits, Description [Abstract]
Number of participants domestic pension plan	3,500
Number of participants postretirement benefit plan	1,700
Deferred Compensation Arrangements [Abstract]
Deferred compensation liability	$ 96.2	$ 92.4
Deferred compensation expense	11.2	9.7	$ 6.3
Deferred benefit liability	117.0	129.1
Deferred benefit expense	7.3	8.8	$ 9.7
Cash surrender value of life insurance	177.4	171.5
Deferred compensation plan assets	15.9	12.9
Long-Term Disability Plan [Abstract]
Long-term disability plan obligation	8.4	$ 8.2
Long term disability plan, income replacement benefit obligation	$ 0.0

Pension and Postretirement Benefit Obligation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets (Period Start)	$ 461.1
Fair Value of Plan Assets (Period End)	503.0	$ 461.1
Domestic Plan [Member]
Benefit Obligation [Roll Forward]
Benefit obligation (period start)	126.6	126.9
Service cost	0.0	0.0	$ 0.0
Interest cost	5.1	5.9	0.3
Benefits Paid	(11.4)	(13.6)
Plan participant contributions	0.0	0.0
Actuarial losses (gains)	5.1	7.4
Settlements and curtailments	0.0	0.0
Foreign currency effect	0.0	0.0
Other	0.0	0.0
Benefit Obligation (Period End)	125.4	126.6	126.9
Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets (Period Start)	95.2	101.1
Actual return on plan assets	12.4	7.7
Employer contributions	2.6	0.0
Plan participant contributions	0.0	0.0
Benefits paid	(11.4)	(13.6)
Settlements	0.0	0.0
Foreign currency effect	0.0	0.0
Other	0.0	0.0
Fair Value of Plan Assets (Period End)	98.8	95.2	101.1
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(26.6)	(31.4)
Amounts Recognized in Consolidated Balance Sheets
Non-current asset	0.0	0.0
Current liability	0.0	0.0
Non-current liability	(26.6)	(31.4)
Net liability recognized	(26.6)	(31.4)
Accumulated benefit obligation	125.4	126.6
Amounts recognized in Accumulated Other Comprehensive Loss, net
Net actuarial loss	52.2	54.9
Prior service cost (credit)	0.0	0.0
Total amount recognized	52.2	54.9
Net actuarial losses from AOCI into net periodic cost	1.5
Pension plans with underfunded or unfunded accumulated benefit obligation
Aggregate projected benefit obligation	125.4	126.6
Aggregate accumulated benefit obligation	125.4	126.6
Aggregate fair value of plan assets	98.8	95.2
Foreign Plan [Member]
Benefit Obligation [Roll Forward]
Benefit obligation (period start)	530.6	537.9
Service cost	4.9	6.7	11.1
Interest cost	13.5	15.1	18.9
Benefits Paid	(19.0)	(25.7)
Plan participant contributions	0.2	0.2
Actuarial losses (gains)	20.3	115.6
Settlements and curtailments	(19.8)	(6.3)
Foreign currency effect	50.4	(84.2)
Other	1.2	(28.7)
Benefit Obligation (Period End)	582.3	530.6	537.9
Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets (Period Start)	365.9	399.6
Actual return on plan assets	25.1	47.9
Employer contributions	17.5	23.2
Plan participant contributions	0.2	0.2
Benefits paid	(19.0)	(25.7)
Settlements	(19.1)	(2.2)
Foreign currency effect	33.2	(68.6)
Other	0.4	(8.5)
Fair Value of Plan Assets (Period End)	404.2	365.9	399.6
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(178.1)	(164.7)
Amounts Recognized in Consolidated Balance Sheets
Non-current asset	9.0	7.6
Current liability	(6.5)	(5.5)
Non-current liability	(180.6)	(166.8)
Net liability recognized	(178.1)	(164.7)
Accumulated benefit obligation	577.9	526.2
Amounts recognized in Accumulated Other Comprehensive Loss, net
Net actuarial loss	201.6	183.4
Prior service cost (credit)	1.1	0.9
Total amount recognized	202.7	184.3
Net actuarial losses from AOCI into net periodic cost	6.0
Pension plans with underfunded or unfunded accumulated benefit obligation
Aggregate projected benefit obligation	576.6	525.3
Aggregate accumulated benefit obligation	575.2	523.8
Aggregate fair value of plan assets	389.5	352.9
Other Postretirement Benefits Plan [Member]
Benefit Obligation [Roll Forward]
Benefit obligation (period start)	32.3	33.9
Service cost	0.0	0.0	0.0
Interest cost	1.3	1.5	1.5
Benefits Paid	(5.9)	(5.8)
Plan participant contributions	1.6	1.6
Actuarial losses (gains)	2.5	1.1
Settlements and curtailments	0.0	0.0
Foreign currency effect	0.0	0.0
Other	0.0	0.0
Benefit Obligation (Period End)	31.8	32.3	33.9
Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets (Period Start)	0.0	0.0
Actual return on plan assets	0.0	0.0
Employer contributions	4.3	4.2
Plan participant contributions	1.6	1.6
Benefits paid	(5.9)	(5.8)
Settlements	0.0	0.0
Foreign currency effect	0.0	0.0
Other	0.0	0.0
Fair Value of Plan Assets (Period End)	0.0	0.0	$ 0.0
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(31.8)	(32.3)
Amounts Recognized in Consolidated Balance Sheets
Non-current asset	0.0	0.0
Current liability	(3.1)	(3.2)
Non-current liability	(28.7)	(29.1)
Net liability recognized	(31.8)	(32.3)
Amounts recognized in Accumulated Other Comprehensive Loss, net
Net actuarial loss	4.2	1.7
Prior service cost (credit)	(0.4)	(0.6)
Total amount recognized	3.8	$ 1.1
Other Foreign Pension Plans
Fair Value of Plan Assets [Roll Forward]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	$ 56.2

Net Periodic Cost (Details) - USD ($) $ in Millions	12 Months Ended
Net Periodic Cost (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Domestic Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost
Service cost	$ 0.0	$ 0.0	$ 0.0
Interest cost	5.1	5.9	0.3
Expected return on plan assets	(6.2)	(6.6)	(7.6)
Settlement and curtailment losses (gains)	0.0	0.0	0.0
Amortization of:
Prior service cost (credit)	0.0	0.0	0.0
Net actuarial losses	1.5	1.3	6.5
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ 0.4	$ 0.6	$ (0.8)
Discount rate	4.20%	4.80%	4.15%
Expected return on plan assets	7.00%	7.00%	7.00%
Discount rate	3.70%	4.20%	4.80%
Foreign Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost
Service cost	$ 4.9	$ 6.7	$ 11.1
Interest cost	13.5	15.1	18.9
Expected return on plan assets	(17.7)	(18.7)	(20.6)
Settlement and curtailment losses (gains)	6.8	0.4	(0.2)
Amortization of:
Prior service cost (credit)	0.1	0.1	0.1
Net actuarial losses	5.5	4.2	4.1
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ 13.1	$ 7.8	$ 13.4
Discount rate	2.52%	3.61%	3.41%
Rate of compensation increase	2.36%	3.18%	2.99%
Expected return on plan assets	4.66%	5.38%	5.01%
Discount rate	2.36%	2.52%	3.61%
Rate of compensation increase	2.37%	2.36%	3.25%
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost
Service cost	$ 0.0	$ 0.0	$ 0.0
Interest cost	1.3	1.5	1.5
Expected return on plan assets	0.0	0.0	0.0
Settlement and curtailment losses (gains)	0.0	0.0	0.0
Amortization of:
Prior service cost (credit)	(0.2)	(0.2)	(0.1)
Net actuarial losses	0.0	0.0	0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ 1.1	$ 1.3	$ 1.4
Discount rate	4.05%	4.65%	4.00%
Discount rate	3.65%	4.05%	4.65%
Health care cost trend rate assumed for next year	6.50%	6.75%	7.00%
Year ultimate rate is reached	2024	2024	2024
Ultimate rate	5.00%	5.00%	5.00%

Fair Value of Pension Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	$ 503.0	$ 461.1
Investment funds
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	14.7	14.4
Limited partnerships
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	29.5	28.0
Fixed income securities
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	23.4	22.9
Insurance contracts
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	7.9	7.8
Other plan assets
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	27.7	20.1
Total plan assets subject to leveling
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	103.2	93.2
Investments measured at net asset value
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	399.8	367.9
Level 1 \| Investment funds
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	14.7	14.4
Level 1 \| Limited partnerships
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	0.0	0.0
Level 1 \| Fixed income securities
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	23.4	22.6
Level 1 \| Insurance contracts
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	0.0	0.0
Level 1 \| Other plan assets
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	27.7	20.1
Level 1 \| Total plan assets subject to leveling
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	65.8	57.1
Level 2 \| Investment funds
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	0.0	0.0
Level 2 \| Limited partnerships
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	0.0	0.0
Level 2 \| Fixed income securities
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	0.0	0.3
Level 2 \| Insurance contracts
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	7.9	7.8
Level 2 \| Other plan assets
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	0.0	0.0
Level 2 \| Total plan assets subject to leveling
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	7.9	8.1
Level 3 \| Investment funds
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	0.0	0.0
Level 3 \| Limited partnerships
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	29.5	28.0
Balance at beginning of period	28.0	31.0
Actual return on plan assets	1.5	(3.0)
Balance at end of period	29.5	28.0
Level 3 \| Fixed income securities
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	0.0	0.0
Level 3 \| Insurance contracts
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	0.0	0.0
Level 3 \| Other plan assets
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	0.0	0.0
Level 3 \| Total plan assets subject to leveling
Fair value assets and liabilities measured on recurring basis
Defined Benefit Plan, Fair Value of Plan Assets	$ 29.5	$ 28.0

Employee Benefits Allocation of Plan Assets (Details)	Dec. 31, 2017	Dec. 31, 2016
Allocation of Plan Assets
Defined benefit plan, plan assets, target allocation, percentage	100.00%
Defined benefit plan, actual plan asset allocations	100.00%	100.00%
Alternative Investments
Allocation of Plan Assets
Defined benefit plan, plan assets, target allocation, percentage	27.00%
Defined benefit plan, actual plan asset allocations	27.00%	21.00%
Equity securities
Allocation of Plan Assets
Defined benefit plan, plan assets, target allocation, percentage	23.00%
Defined benefit plan, actual plan asset allocations	23.00%	23.00%
Fixed income securities
Allocation of Plan Assets
Defined benefit plan, plan assets, target allocation, percentage	21.00%
Defined benefit plan, actual plan asset allocations	21.00%	26.00%
Liability driven investments
Allocation of Plan Assets
Defined benefit plan, plan assets, target allocation, percentage	14.00%
Defined benefit plan, actual plan asset allocations	14.00%	14.00%
Real estate
Allocation of Plan Assets
Defined benefit plan, plan assets, target allocation, percentage	6.00%
Defined benefit plan, actual plan asset allocations	6.00%	6.00%
Other plan assets
Allocation of Plan Assets
Defined benefit plan, plan assets, target allocation, percentage	9.00%
Defined benefit plan, actual plan asset allocations	9.00%	10.00%

Pension Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
Pension Cash Flows (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans
Estimated U.S. federal subsidies expected to be received under the Medicare Prescription Drug, Improvement and Modernization Act of 2003, no more than	$ 0.3
Domestic Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans
Employer contributions	2.6	$ 0.0
Defined benefit plan, estimated future employer contributions in next fiscal year	10.0
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity
Expected future benefit payments in 2018	13.7
Expected future benefit payments in 2019	8.5
Expected future benefit payments in 2020	8.6
Expected future benefit payments in 2021	8.0
Expected future benefit payments in 2022	8.4
Expected future benefit payments in 2023-2027	37.2
Foreign Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans
Employer contributions	17.5	23.2
Defined benefit plan, estimated future employer contributions in next fiscal year	18.0
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity
Expected future benefit payments in 2018	22.3
Expected future benefit payments in 2019	23.8
Expected future benefit payments in 2020	21.6
Expected future benefit payments in 2021	22.3
Expected future benefit payments in 2022	23.5
Expected future benefit payments in 2023-2027	124.0
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans
Employer contributions	4.3	$ 4.2
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity
Expected future benefit payments in 2018	3.2
Expected future benefit payments in 2019	3.0
Expected future benefit payments in 2020	2.8
Expected future benefit payments in 2021	2.6
Expected future benefit payments in 2022	2.4
Expected future benefit payments in 2023-2027	$ 10.4

Savings Plans (Details) - USD ($) $ in Millions	12 Months Ended
Savings Plans (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Domestic Tax Authority
Defined Benefit Plans and Other Postretirement Benefit Plans
Cost Recognized	$ 47.2	$ 47.0	$ 44.5
Discretionary Company Contribution
Defined Benefit Plans and Other Postretirement Benefit Plans
Cost Recognized	3.6	6.1	5.8
Defined Contribution Plans Participant Forfeitures
Defined Benefit Plans and Other Postretirement Benefit Plans
Cost Recognized	4.6	4.4	3.8
Foreign Tax Authority
Defined Benefit Plans and Other Postretirement Benefit Plans
Cost Recognized	$ 47.4	$ 44.5	$ 43.9

Segment Operations (Details) - USD ($)
$ in Millions

3 Months Ended

12 Months Ended

Dec. 31, 2017

Sep. 30, 2017

Jun. 30, 2017

Mar. 31, 2017

Dec. 31, 2016

Sep. 30, 2016

Jun. 30, 2016

Mar. 31, 2016

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Segments:

Revenue

$ 2,341.0

$ 1,902.6

$ 1,884.9

$ 1,753.9

$ 2,264.5

$ 1,922.2

$ 1,917.9

$ 1,742.0

$ 7,882.4

$ 7,846.6

$ 7,613.8

Segment operating income

973.6

941.0

874.8

Interest expense

(90.8)

(90.6)

(85.8)

Interest income

19.4

20.1

22.8

Other expense, net

(1.7)

^[1],[2]

$ (9.9)

^[1],[2]

$ (15.4)

^[1],[2]

$ 0.8

^[1],[2]

(26.8)

^[1],[2]

$ 5.3

^[1],[2]

$ 0.4

^[1],[2]

$ (19.2)

^[1],[2]

(26.2)

(40.3)

(49.6)

Income before income taxes

876.0

830.2

762.2

Depreciation and amortization of fixed assets and intangible assets

157.1

160.2

157.0

Capital expenditures

155.9

200.7

161.1

Assets

12,695.2

12,485.2

12,695.2

12,485.2

IAN

Segments:

Revenue

6,397.3

6,319.4

6,145.4

Segment operating income

907.4

898.2

850.3

Depreciation and amortization of fixed assets and intangible assets

111.8

117.7

117.5

Capital expenditures

112.0

149.2

117.5

Assets

10,973.0

10,660.0

10,973.0

10,660.0

CMG

Segments:

Revenue

1,485.1

1,527.2

1,468.4

Segment operating income

192.8

190.0

166.3

Depreciation and amortization of fixed assets and intangible assets

20.4

19.5

18.4

Capital expenditures

17.7

16.6

12.7

Assets

1,422.9

1,428.3

1,422.9

1,428.3

Corporate and Other

Segments:

Segment operating income

(126.6)

(147.2)

(141.8)

Depreciation and amortization of fixed assets and intangible assets

24.9

23.0

21.1

Capital expenditures

26.2

34.9

$ 30.9

Assets

$ 299.3

$ 396.9

$ 299.3

$ 396.9

[1]	As part of the adoption of FASB ASU 2017-07, we have reclassified a portion of postretirement costs from salaries and related expenses to other income (expense), net.
[2]	The three months ended June 30 and September 30, 2017 included pre-tax net losses of $13.1 and $8.7, respectively, on sales of businesses. The three months ended March 31 and December 31, 2016 included pre-tax net losses of $16.3 and $25.3, respectively, on sales of businesses.

Segment Information Major Geographic Area (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues and Long-Lived Assets
Revenue	$ 2,341.0	$ 1,902.6	$ 1,884.9	$ 1,753.9	$ 2,264.5	$ 1,922.2	$ 1,917.9	$ 1,742.0	$ 7,882.4	$ 7,846.6	$ 7,613.8
Long-Lived Assets	1,045.1				1,004.4				1,045.1	1,004.4
Domestic
Revenues and Long-Lived Assets
Revenue									4,714.3	4,684.8	4,475.5
Long-Lived Assets	705.5				684.8				705.5	684.8
Total International
Revenues and Long-Lived Assets
Revenue									3,168.1	3,161.8	3,138.3
Long-Lived Assets	339.6				319.6				339.6	319.6
United Kingdom
Revenues and Long-Lived Assets
Revenue									681.8	695.7	687.7
Long-Lived Assets	56.2				52.0				56.2	52.0
Continental Europe
Revenues and Long-Lived Assets
Revenue									716.1	699.8	697.2
Long-Lived Assets	73.6				57.0				73.6	57.0
Asia Pacific
Revenues and Long-Lived Assets
Revenue									913.6	923.0	916.9
Long-Lived Assets	115.5				118.3				115.5	118.3
Latin America
Revenues and Long-Lived Assets
Revenue									355.9	372.7	383.5
Long-Lived Assets	48.2				49.0				48.2	49.0
Other
Revenues and Long-Lived Assets
Revenue									500.7	470.6	$ 453.0
Long-Lived Assets	$ 46.1				$ 43.3				$ 46.1	$ 43.3

Commitments and Contingencies Net Rent Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Gross rent expense	$ 371.0	$ 366.1	$ 336.5
Third-party sublease rental income	(4.6)	(4.1)	(5.5)
Net rent expense	$ 366.4	$ 362.0	$ 331.0

Future Minimum Lease Payments (Details) $ in Millions	Dec. 31, 2017 USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Rent Obligations, due 2018	$ 335.0
Rent Obligations, due 2019	312.1
Rent Obligations, due 2020	285.3
Rent Obligations, due 2021	251.4
Rent Obligations, due 2022	204.1
Rent Obligations, due thereafter	727.2
Total Rent Obligations	2,115.1
Sublease Rental Income, due 2018	(4.2)
Sublease Rental Income, due 2019	(3.8)
Sublease Rental Income, due 2020	(2.5)
Sublease Rental Income, due 2021	(1.4)
Sublease Rental Income, due 2022	(0.8)
Sublease Rental Income, due thereafter	(0.5)
Total Sublease Rental Income	(13.2)
Net Rent, due 2018	330.8
Net Rent, due 2019	308.3
Net Rent, due 2020	282.8
Net Rent, due 2021	250.0
Net Rent, due 2022	203.3
Net Rent, due thereafter	726.7
Total Net Rent	$ 2,101.9

Guarantees (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Parent company guarantees on lease obligations	$ 829.2	$ 857.3
Parent company guarantees relating to credit facilities	491.0	$ 395.6
Assets pledged as security for parent company guarantees	$ 0.0

Contingent Acquisition Obligations (Details)
$ in Millions

Dec. 31, 2017

USD ($)

Deferred acquisition payments

Business Acquisition, Contingent Consideration [Line Items]

Future contingent acquisition obligation due in 2018

$ 41.9

Future contingent acquisition obligation due in 2019

27.5

Future contingent acquisition obligation due in 2020

16.1

Future contingent acquisition obligation due in 2021

24.4

Future contingent acquisition obligation due in 2022

4.8

Future contingent acquisition obligation due thereafter

6.3

Future contingent acquisition obligation due, total

121.0

Redeemable noncontrolling interests and call options with affiliates

Business Acquisition, Contingent Consideration [Line Items]

Future contingent acquisition obligation due in 2018

37.1

^[1]

Future contingent acquisition obligation due in 2019

26.4

^[1]

Future contingent acquisition obligation due in 2020

62.9

^[1]

Future contingent acquisition obligation due in 2021

10.3

^[1]

Future contingent acquisition obligation due in 2022

6.6

^[1]

Future contingent acquisition obligation due thereafter

4.1

^[1]

Future contingent acquisition obligation due, total

147.4

^[1]

Redeemable at noncontrolling equity owners discretion

Business Acquisition, Contingent Consideration [Line Items]

Future contingent acquisition obligation due in 2018

24.8

Total contingent acquisition payments

Business Acquisition, Contingent Consideration [Line Items]

Future contingent acquisition obligation due in 2018

79.0

Future contingent acquisition obligation due in 2019

53.9

Future contingent acquisition obligation due in 2020

79.0

Future contingent acquisition obligation due in 2021

34.7

Future contingent acquisition obligation due in 2022

11.4

Future contingent acquisition obligation due thereafter

10.4

Future contingent acquisition obligation due, total

$ 268.4

[1]

Recent Accounting Standards Recent Accounting Standards (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Net periodic costs excluding service costs	$ 9.6	$ 3.0	$ 2.9
Restricted cash and cash equivalents	6.8	$ 2.6	$ 3.2	$ 3.8
Increase in third-party costs due to revenue standard low range	1,100.0
Increase in third-party costs due to revenue standard high range	$ 1,300.0

Results by Quarter (Unaudited) (Details) - USD ($)
$ / shares in Units, $ in Millions

3 Months Ended

12 Months Ended

Dec. 31, 2017

Sep. 30, 2017

Jun. 30, 2017

Mar. 31, 2017

Dec. 31, 2016

Sep. 30, 2016

Jun. 30, 2016

Mar. 31, 2016

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Quarterly Financial Information Disclosure [Abstract]

Revenue

$ 2,341.0

$ 1,902.6

$ 1,884.9

$ 1,753.9

$ 2,264.5

$ 1,922.2

$ 1,917.9

$ 1,742.0

$ 7,882.4

$ 7,846.6

$ 7,613.8

Salaries and related expenses

1,325.8

^[1]

1,227.6

^[1]

1,239.3

^[1]

1,275.4

^[1]

1,308.8

^[1]

1,228.0

^[1]

1,229.5

^[1]

1,268.8

^[1]

5,068.1

5,035.1

4,854.8

Office and general expenses

496.9

455.9

439.1

448.8

470.0

486.2

464.1

450.2

1,840.7

1,870.5

1,884.2

Operating income

518.3

219.1

206.5

29.7

485.7

208.0

224.3

23.0

973.6

941.0

874.8

Other income (expense), net

(1.7)

^[1],[2]

(9.9)

^[1],[2]

(15.4)

^[1],[2]

0.8

^[1],[2]

(26.8)

^[1],[2]

5.3

^[1],[2]

0.4

^[1],[2]

(19.2)

^[1],[2]

(26.2)

(40.3)

(49.6)

Total (expenses) and other income

(19.5)

(26.8)

(36.4)

(14.9)

(44.6)

(11.7)

(18.5)

(36.0)

(97.6)

(110.8)

(112.6)

(Benefit of) provision for income taxes

166.1

^[3]

42.5

^[3]

75.4

^[3]

(2.1)

^[3]

106.1

^[3]

63.8

^[3]

43.7

^[3]

(15.6)

^[3]

281.9

198.0

282.8

Net income

333.5

148.8

94.6

18.1

336.9

132.7

160.2

2.7

$ 595.0

$ 632.5

$ 480.5

Net income available to IPG common stockholders

$ 316.6

$ 146.2

$ 94.7

$ 21.5

$ 317.6

$ 128.6

$ 156.9

$ 5.4

Basic earnings per share

$ 0.82

$ 0.38

$ 0.24

$ 0.05

$ 0.81

$ 0.32

$ 0.39

$ 0.01

$ 1.49

$ 1.53

$ 1.11

Diluted earnings per share

0.81

0.37

0.24

0.05

0.78

0.32

0.38

0.01

1.46

1.49

1.09

Dividends declared per common share

$ 0.18

$ 0.15

$ 0.72

$ 0.60

$ 0.48

Pre-tax losses on sales of businesses

$ 8.7

$ 13.1

$ 25.3

$ 16.3

Foreign tax credits

$ 31.2

Net impact of the Tax Act

$ 36.0

$ 0.0

Tax benefit (reversal of valuation allowance)

12.2

Tax benefit (conclusion and settlement of a tax examination of previous years)

$ 23.4

Tax benefit (refunds to be claimed on future amended U.S. federal tax returns)

$ 37.4

[1]	As part of the adoption of FASB ASU 2017-07, we have reclassified a portion of postretirement costs from salaries and related expenses to other income (expense), net.
[2]	The three months ended June 30 and September 30, 2017 included pre-tax net losses of $13.1 and $8.7, respectively, on sales of businesses. The three months ended March 31 and December 31, 2016 included pre-tax net losses of $16.3 and $25.3, respectively, on sales of businesses.
[3]	The three months ended September 30, 2017 included a tax benefit of $31.2 related to foreign tax credits from distributions of unremitted earnings, which was reversed during the three months ended December 31, 2017 as a result of the enactment of the Tax Cuts and Jobs Act. The three months ended December 31, 2017 included a net tax benefit of $36.0 as a result of the enactment of the Tax Cuts and Jobs Act. The three months ended March 31, 2016 included a tax benefit of $12.2 due to the reversal of valuation allowances. The three months ended June 30, 2016 included a tax benefit of $23.4 related to the conclusion and settlement of a tax examination of previous years. The three months ended December 31, 2016 included a tax benefit of $37.4 for refunds to be claimed on future amended U.S. federal returns.

Subsequent Events (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares
Subsequent Event [Line Items]
Dividends payable, amount per share \| $ / shares	$ 0.21
Dividends payable, date to be paid	Mar. 15, 2018
Dividends payable, date of record	Mar. 01, 2018
2018 Share Repurchase Program
Subsequent Event [Line Items]
Share repurchase program, initial authorized amount \| $	$ 300.0

Debt and Credit Agreements Cash Pooling (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
Cash debt pooling arrangements, amount netted	$ 1,412.0	$ 1,300.6