Business Combination Disclosure [Text Block]

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 2018, we completed five acquisitions, one of which was included in the IAN reportable segment, three of which were included in the CMG reportable segment, and Acxiom which is included in the "Corporate and other" group. See Note 6 for discussion of our acquisition of Acxiom. These acquisitions include a full-service digital agency based in Brazil, an entertainment marketing and brand licensing agency in the fashion and lifestyle sector based in the U.K., a content-focused social creative agency based in the U.K., a data and technology company based in the U.S., and a content production firm based in Israel. During 2018, we recorded approximately $2,131.0 of goodwill and other intangible assets related to our acquisitions.

During 2017, we completed ten acquisitions, eight of which were included in the IAN reportable segment, and two of which were included in the CMG reportable 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 2017, we recorded approximately $62.0 of goodwill and other intangible assets related to our acquisitions.

During 2016, we completed ten acquisitions, three of which were included in the IAN reportable segment, and seven of which was included in the CMG reportable 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 2016, we recorded approximately $149.0 of goodwill and other intangible assets related to our 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 2018, 2017 or 2016.

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



	Years ended December 31,
	2018			2017			2016
Cost of investment: current-year acquisitions ¹	$	2,323.4		$	36.8		$	65.7
Cost of investment: prior-year acquisitions	33.9			54.6			40.7
Less: net cash acquired	(13.8		)	(7.1		)	(13.6		)
Total cost of investment	2,343.5			84.3			92.8
Operating payments²	19.4			47.1			19.1
Total cash paid for acquisitions ³	$	2,362.9		$	131.4		$	111.9


1	The cost of investment: current-year acquisitions line significantly increased in the year ended December 31, 2018, primarily as a result of payments related to the acquisition of Acxiom. See Note 6 for further information on the Acxiom Acquisition.

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, $2,309.8, $30.6 and $52.0 for the years ended December 31, 2018, 2017 and 2016, 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, $33.7, $53.7 and $40.8 for the years ended December 31, 2018, 2017 and 2016, 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 15 for further information on contingent acquisition obligations. Redeemable noncontrolling interests are adjusted quarterly, if necessary, to their estimated redemption value, but not less than their initial fair value. Any adjustments to the redemption value impact retained earnings or additional paid in capital, except for foreign currency translation adjustments. The following table presents changes in our redeemable noncontrolling interests.



	Years ended December 31,
	2018			2017			2016
Balance at beginning of period	$	252.1		$	252.8		$	251.9
Change in related noncontrolling interests balance	(10.7		)	(2.8		)	4.9
Changes in redemption value of redeemable noncontrolling interests:
Additions	—			7.7			6.8
Redemptions and other	(33.7		)	(18.5		)	(14.8		)
Redemption value adjustments	(39.8		)	12.9			4.0
Balance at end of period	$	167.9		$	252.1		$	252.8

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.

Acxiom Acquisition (Notes)

12 Months Ended

Dec. 31, 2018

Business Combination Disclosure [Text Block]

Acxiom Acquisition

On October 1, 2018, pursuant to the terms of the Membership Interest Purchase Agreement dated as of July 2, 2018, the Company completed the acquisition of Acxiom Holdings, Inc.’s Marketing Solutions business ("Acxiom") through the acquisition of 100% of the equity interests of Acxiom for $2,327.9, subject to customary closing adjustments. The purpose of the acquisition is to combine the Company's media, creative, marketing services and analytics capabilities, global scale and consumer insights, with Acxiom's expertise in identity, data, integrations and data stewardship.

The Company funded the acquisition of Acxiom from a term loan agreement with third-party lenders for $500.0 and unsecured senior notes issued for a total of $2,000.0 in aggregate principal amount. See Note 3 for further information regarding the Company's debt.

The following table summarizes the preliminary fair values of the assets acquired and liabilities assumed at the closing date:



	October 1, 2018
Cash and cash equivalents	$	13.3
Accounts receivable	112.9
Accounts receivable, billable to clients	8.3
Other current assets	28.2
Property and equipment, net	159.7
Deferred income taxes	(0.6		)
Goodwill	1,110.8
Intangible assets, net	995.0
Other non-current assets	8.3
Accounts payable	(37.1		)
Accrued liabilities	(46.9		)
Contract liabilities	(23.2		)
Other non-current liabilities	(0.8		)
Net assets acquired	$	2,327.9

The preliminary fair values of the identifiable intangible assets acquired at the closing date are as follows:



	Fair Value		Weighted Average Amortization Period (Years)
Customer lists	$	600.0	15.0
Know-how and technology	235.0		9.0
Trade names	160.0		15.0 to indefinite
Total intangible assets	995.0

The preliminary fair value of the customer lists was determined by applying the multi-period excess earnings method, a variation of the income approach. The preliminary fair values of the know-how and technology and the trade names were determined using the relief from royalty method of the income approach. Goodwill generated by the Acxiom Acquisition, the majority of which is tax deductible, primarily relates to intangible assets that do not qualify for separate recognition, including assembled workforce and synergies. The purchase accounting process has not been completed primarily because the valuation of acquired assets has not been finalized. We expect to complete the purchase accounting as soon as practicable but no later than one year from the acquisition date. We do not believe there will be material adjustments.

The operating results of Acxiom for the period from October 1, 2018 to December 31, 2018, including net revenue of $181.7 and net income available to IPG common stockholders of $20.4, are included in our Consolidated Statements of Operations for the year ended December 31, 2018.

The Company incurred a total of $35.0 in "Selling, general and administrative expenses," $3.7 in "Interest expense," $0.4 in "Interest income" and $10.3 in "Other expense, net," for transaction-related costs in connection with the acquisition.

The following table presents the combined results of the Company and Acxiom for the years ended December 31, 2018 and 2017 on an unaudited pro forma basis, as if the acquisition had occurred on January 1, 2017. The unaudited pro forma financial information is presented for informational purposes only and is not indicative of the results of operations that would have been achieved if that acquisition had taken place at the beginning of January 1, 2017. It also does not reflect changes in cost structure or operations resulting from restructuring activities, changes in the business, or future events that may occur after the completion of the acquisition. The pro forma combined results of operations shown below include after-tax nonrecurring transaction-related charges of $27.6 in 2017, and the business combination accounting effects resulting from the acquisition.



	(unaudited)
	December 31,
	2018		2017
Pro forma revenues	$	10,230.4	$	9,736.1
Pro forma net income	642.2		519.2

Supplementary Data (Notes)

12 Months Ended

Dec. 31, 2018

Supplementary Data [Abstract]

Supplementary Data

Valuation and Qualifying Accounts – Allowance for Uncollectible Accounts Receivable



	Years ended December 31,
	2018			2017			2016
Balance at beginning of period	$	42.7		$	55.7		$	54.2
Charges to costs and expenses	6.5			9.5			16.7
Adjustments:
Acquisitions/(dispositions)	2.2			(1.0		)	(2.5		)
Uncollectible accounts written off	(7.1		)	(25.5		)	(9.4		)
Foreign currency translation adjustments	(1.8		)	4.0			(3.3		)
Balance at end of period	$	42.5		$	42.7		$	55.7

Property and Equipment



	December 31,
	2018			2017
Furniture and equipment	$	681.7		$	634.8
Leasehold improvements	629.0			641.5
Internal-use computer software	368.5			331.3
Land and buildings	146.6			79.0
Gross property and equipment	1,825.8			1,686.6
Less: accumulated depreciation	(1,034.9		)	(1,036.2		)
Total property and equipment, net	$	790.9		$	650.4

Total depreciation and amortization expense for property and equipment for the years ended December 31, 2018, 2017 and 2016 was $165.3, $136.0 and $138.3, respectively.

Accrued Liabilities

The following table presents the components of accrued liabilities.



	December 31,
	2018		2017
Salaries, benefits and related expenses	$	494.9	$	441.7
Acquisition obligations	65.7		42.0
Office and related expenses	52.2		53.2
Interest	43.6		16.4
Other	150.5		121.4
Total accrued liabilities	$	806.9	$	674.7

Other Expense, Net

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



	Years ended December 31,
	2018			2017			2016
Net losses on sales of businesses	$	(61.9	)	$	(24.1	)	$	(41.4	)
Other	(7.7		)	(2.1		)	1.1
Total other expense, net	$	(69.6	)	$	(26.2	)	$	(40.3	)

Net losses on sales of businesses – During 2018, the amounts recognized were related to sales of businesses and the classification of certain assets and liabilities, consisting primarily of cash, as held for sale within our IAN and CMG reportable segments. 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 2017, the amounts recognized were 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 reportable segment. 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 reportable segments.

Other – During 2018, the amounts recognized were primarily a result of transaction-related costs from the Acxiom Acquisition.

Share Repurchase Program

In February 2018, 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, which was in addition to the remaining amount available to be repurchased from the $300.0 authorization made by the Board in February 2017.

We may effect such repurchases through open market purchases, trading plans established in accordance with SEC rules, derivative transactions or other means. The timing and amount of repurchases in future periods 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,
	2018		2017		2016
Number of shares repurchased	5.1		13.7		13.3
Aggregate cost, including fees	$	117.1	$	300.1	$	303.3
Average price per share, including fees	$	23.03	$	21.97	$	22.76

On July 2, 2018, in connection with the announcement of the Acxiom acquisition, we announced that share repurchases will be suspended for a period of time in order to reduce the increased debt levels incurred in conjunction with the acquisition. As of December 31, 2018, $338.4 remained available for repurchase under the share repurchase programs, which has no expiration date.

Supplemental Cash Flow Information



	Years ended December 31,
	2018		2017		2016
Cash paid for interest	$	88.7	$	82.3	$	78.8
Cash paid for income taxes, net of refunds ¹	207.9		228.4		244.1


1	Refunds of $24.3, $31.9 and $26.6 were received for the years ended December 31, 2018, 2017 and 2016, respectively.

Goodwill and Other Intangible Assets (Notes)

12 Months Ended

Dec. 31, 2018

Goodwill and Intangible Assets [Abstract]

Goodwill and Intangible Assets Disclosure [Text Block]

Goodwill and Other 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, CMG and Corporate & other, for the years ended December 31, 2018 and 2017 are listed below.



	IAN			CMG			Corporate & other ¹			Total ²
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
Acquisitions	1.2			20.0			1,110.8			1,132.0
Foreign currency and other	(63.3		)	(12.0		)	(1.2		)	(76.5		)
Balance as of December 31, 2018	$	3,099.7		$	666.6		$	1,109.6		$	4,875.9


1	During 2018, the increase in goodwill is primarily due to the acquisition of Acxiom. See Note 6 for further information on the Acxiom Acquisition.


2	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 primarily consist of customer lists and know-how and technology, which have definite lives and are subject to amortization on a straight-line basis with estimated useful lives generally between 7 and 15 years, as well as trade names which have both indefinite and definite lives which are subject to amortization on a straight-line basis with estimated useful lives of 15 years. Amortization expense for other intangible assets for the years ended December 31, 2018, 2017 and 2016 was $37.6, $21.1 and $21.9, respectively. There were no material impairment charges on other intangibles for the years ended December 31, 2018, 2017 and 2016. During 2018 and 2017, we recorded approximately $999.0 and $7.0 of other intangible assets related to our acquisitions in the respective year. The increase in 2018 is primarily due to the acquisition of Acxiom.

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



	December 31,
	2018							2017
	Gross Amount		Accumulated Amortization			Net Amount		Gross Amount		Accumulated Amortization			Net Amount
Customer lists	$	857.2	$	(190.9	)	$	666.3	$	267.3	$	(172.2	)	$	95.1
Know-how and technology	235.0		(6.5		)	228.5		—		—			—
Trade names	226.2		(36.8		)	189.4		68.8		(33.8		)	35.0
Other	14.4		(3.8		)	10.6		14.4		(3.8		)	10.6
Total	$	1,332.8	$	(238.0	)	$	1,094.8	$	350.5	$	(209.8	)	$	140.7

The estimated annual amortization expense for other intangible assets for the next five years as of December 31, 2018 is listed below.



	2019		2020		2021		2022		2023
Estimated amortization expense	$	87.8	$	87.3	$	85.6	$	82.3	$	78.2

Income Taxes (Notes)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Income Tax Disclosure [Text Block]

Income Taxes

The components of income before income taxes are listed below.



	Years ended December 31,
	2018		2017		2016
Domestic	$	474.0	$	514.8	$	502.1
Foreign	364.0		326.0		323.5
Total	$	838.0	$	840.8	$	825.6

The provision for income taxes is listed below.



	Years ended December 31,
	2018			2017			2016
U.S. federal income taxes (including foreign withholding taxes):
Current	$	38.1		$	154.1		$	54.3
Deferred	29.9			(37.6		)	35.7
	68.0			116.5			90.0
State and local income taxes:
Current	25.1			18.8			8.2
Deferred	3.4			19.7			(1.6		)
	28.5			38.5			6.6
Foreign income taxes:
Current	121.9			107.9			89.8
Deferred	(19.2		)	8.4			10.5
	102.7			116.3			100.3
Total	$	199.2		$	271.3		$	196.9

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,
	2018			2017			2016
U.S. federal statutory income tax rate	21.0		%	35.0		%	35.0		%

Income tax provision at U.S. federal statutory rate	$	176.0		$	294.3		$	289.0
State and local income taxes, net of U.S. federal income tax benefit	23.8			23.5			4.3
Impact of foreign operations, including withholding taxes	50.7			(6.7		)	(23.9		)
U.S. tax incentives	(17.5		)	(1.3		)	(1.3		)
Change in net valuation allowance ¹	(16.9		)	1.4			(13.4		)
Divestitures	11.7			1.1			9.7
U.S. federal tax credits	(48.1		)	(0.4		)	(44.6		)
Stock compensation	(6.8		)	(15.3		)	(9.0		)
Increase/(decrease) in unrecognized tax benefits	8.4			7.0			(21.8		)
Net impact of the Tax Act	13.4			(36.0		)	0.0
Statutory tax rate changes	0.0			0.0			11.4
Other	4.5			3.7			(3.5		)
Provision for income taxes	$	199.2		$	271.3		$	196.9

Effective income tax rate on operations	23.8		%	32.3		%	23.8		%


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

In 2018, our effective income tax rate of 23.8% was positively impacted by U.S. tax incentives, foreign tax credits from a distribution of unremitted earnings, the net reversal of valuation allowance in Continental Europe and research and development credits. The effective income tax rate was negatively impacted by losses in certain foreign jurisdictions where we receive no tax benefit due to 100% valuation allowances, non-deductible losses on sales of businesses and assets held for sale, by tax expense associated with the change to our assertion regarding the permanent reinvestment of undistributed earnings attributable to certain foreign subsidiaries, and by tax expense related to the true-up of our December 31, 2017 tax reform estimates as permitted by SEC Staff issued Accounting Bulletin No. 118 (“SAB 118”).

Public Law 115-97, commonly referred to as the Tax Cuts and Jobs Act (the "Tax Act") was signed into law on December 22, 2017. The Tax Act legislated many new tax provisions which have impacted our operations. At December 31, 2017, provisional amounts were recorded as permitted by SAB 118. We have finalized our calculations of the impact of the Tax Act and have revised our estimates as required by SAB 118. This resulted in a tax expense of $13.4, primarily attributable to our estimate of the tax imposed on the deemed repatriation of unremitted foreign earnings.

The Tax Act imposed a new tax on certain foreign earnings generated in 2018 and forward. These global intangible low-taxed income ("GILTI") tax rules are complex. U.S. GAAP allows us to choose 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. The Company has elected to account for the GILTI tax as a current expense.

In 2017, our effective income tax rate of 32.3% was positively impacted by a net benefit of $36.0 as a result of the Tax Act as well as 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 the 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.

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



	December 31,
	2018			2017
Postretirement/post-employment benefits	$	17.9		$	19.5
Deferred compensation	99.8			91.7
Pension costs	22.2			27.6
Basis differences in fixed assets	(71.7		)	(52.0		)
Rent	27.3			27.5
Interest	48.8			45.8
Accruals and reserves	21.0			18.4
Allowance for doubtful accounts	7.4			10.2
Basis differences in intangible assets	(302.7		)	(281.3		)
Investments in equity securities	1.2			(3.3		)
Tax loss/tax credit carry forwards	345.6			357.9
Prepaid expenses	(6.3		)	(1.7		)
Deferred revenue	(26.8		)	(41.3		)
Unremitted foreign earnings	(9.5		)	0.0
Other	38.2			43.7
Total deferred tax assets, net	212.4			262.7
Valuation allowance	(211.0		)	(243.0		)
Net deferred tax assets	$	1.4		$	19.7

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,
	2018			2017			2016
Balance at beginning of period	$	243.0		$	255.6		$	275.1
Reversed to costs and expenses	(28.0		)	(4.6		)	(15.4		)
Charged (reversed) to gross tax assets and other accounts ¹	5.1			(27.3		)	9.5
Foreign currency translation	(9.1		)	19.3			(13.6		)
Balance at end of period	$	211.0		$	243.0		$	255.6


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

In 2018, 2017, and 2016, 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, 2018, there were $1,149.4 of loss carryforwards. These loss carryforwards were all non-U.S. tax loss carryforwards, of which $994.1 have unlimited carryforward periods and $155.3 have expiration periods from 2019 to 2038. As of December 31, 2018, the Company also had $26.8 in deferred tax assets for state net operating loss carryforwards and tax credit carryforwards, which will expire between 2019 and 2038.

As of December 31, 2018, we had $1,079.1 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 any deferred taxes on such amounts. During the third quarter ended September 30, 2018, as a result of our increased debt and associated servicing commitments in connection with the Acxiom Acquisition that was consummated on October 1, 2018, the Company re-evaluated its global cash needs and as a result determined that approximately $435.0 of undistributed foreign earnings from certain international entities are no longer subject to the permanent reinvestment assertion. We recorded a tax expense of $10.8 representing our estimate of the tax costs associated with this change to our assertion. We have not changed our permanent reinvestment assertion with respect to any other international entities as we intend to use the related historical earnings and profits to fund international operations and investments.

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



	Years ended December 31,
	2018			2017			2016
Balance at beginning of period	$	271.9		$	246.7		$	226.9
Increases as a result of tax positions taken during a prior year	65.9			6.3			65.0
Decreases as a result of tax positions taken during a prior year	(10.8		)	(8.1		)	(47.5		)
Settlements with taxing authorities	(6.5		)	(0.8		)	(4.6		)
Lapse of statutes of limitation	(1.7		)	(3.3		)	(11.8		)
Increases as a result of tax positions taken during the current year	16.6			31.1			18.7
Balance at end of period	$	335.4		$	271.9		$	246.7

Included in the total amount of unrecognized tax benefits of $335.4 as of December 31, 2018, is $313.5 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, 2018 and 2017 is $42.4 and $27.9, respectively, of which a detriment of $14.5 and $7.0 is included in our 2018 and 2017 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 $15.0 and $25.0 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 2009.

Accumulated Other Comprehensive Loss, Net of Tax (Notes)

12 Months Ended

Dec. 31, 2018

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, 2016	$	(718.6	)	$	0.6		$	(8.4	)	$	(238.0	)	$	(964.4	)
Other comprehensive income (loss) before reclassifications	132.2			0.0			0.0			(9.7		)	122.5
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	$	(585.3	)	$	0.0		$	(6.8	)	$	(235.7	)	$	(827.8	)
Other comprehensive (loss) income before reclassifications	(146.8		)	0.0			0.0			11.4			(135.4		)
Amount reclassified from accumulated other comprehensive loss, net of tax	15.7			0.0			1.5			4.9			22.1
Balance as of December 31, 2018	$	(716.4	)	$	0.0		$	(5.3	)	$	(219.4	)	$	(941.1	)

Amounts reclassified from accumulated other comprehensive loss, net of tax, for the years ended December 31, 2018, 2017 and 2016 are as follows:



	Years ended December 31,									Affected Line Item in the Consolidated Statements of Operations
	2018			2017			2016
Foreign currency translation adjustments ¹	$	15.7		$	1.1		$	3.7		Other expense, net
Gains on available-for-sale securities	0.0			(0.7		)	(1.3		)	Other expense, net
Losses on derivative instruments	2.2			2.1			2.0			Interest expense
Amortization of defined benefit pension and postretirement plans items	6.5			13.7			5.8			Other expense, net
Tax effect	(2.3		)	(2.1		)	(2.1		)	Provision for income taxes
Total amount reclassified from accumulated other comprehensive loss, net of tax	$	22.1		$	14.1		$	8.1


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

Incentive Compensation Plans (Notes)

12 Months Ended

Dec. 31, 2018

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,
	2018		2017		2016
Stock options	$	0.0	$	0.0	$	0.2
Stock-settled awards	24.7		20.5		16.0
Cash-settled awards	0.6		1.0		0.9
Performance-based awards	57.5		61.5		69.4
Employee stock purchase plan	0.9		1.0		0.7
Other ¹	0.9		0.5		0.8
Stock-based compensation expense	$	84.6	$	84.5	$	88.0
Tax benefit	$	20.4	$	30.4	$	32.1


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 after 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, 2018, 2017 and 2016. As of December 31, 2018, all stock options granted were fully vested and exercisable.

The following table summarizes our stock option activity during 2018.



	Options		Weighted- Average Exercise Price (per option)		Weighted- Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Stock options outstanding as of January 1, 2018	3.7		$	9.44
Exercised	(1.9	)	$	8.30
Stock options outstanding as of December 31, 2018	1.8		$	10.66	2.8	$	17.6

There were 1.9, 1.1 and 1.2 stock options exercised in 2018, 2017 and 2016, respectively. The total intrinsic value of stock options exercised during 2018, 2017 and 2016 was $27.9, $15.1 and $15.2, respectively. The cash received from the stock options exercised in 2018, 2017 and 2016 was $29.0, $20.0 and $18.2, which include taxes withheld of $13.3, $6.8, and $7.8, 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, 2018 and 2017.



	Years ended December 31,
	2018		2017		2016
Stock-Settled Awards:
Awards granted	2.1		0.8		1.1
Weighted-average grant-date fair value (per award)	$	23.60	$	24.18	$	21.87
Total fair value of vested awards distributed	$	24.2	$	22.6	$	17.5
Cash-Settled Awards:
Awards granted	0.1		0.0		0.1
Weighted-average grant-date fair value (per award)	$	23.62	$	23.33	$	22.54
Total fair value of vested awards distributed	$	0.8	$	0.9	$	0.7
Performance-Based Awards:
Awards granted	2.9		4.8		3.3
Weighted-average grant-date fair value (per award)	$	21.13	$	20.06	$	19.58
Total fair value of vested awards distributed	$	87.2	$	112.4	$	27.9

In conjunction with common stock dividends declared in 2018 and 2017, we accrued dividends of $2.4 and $1.5, respectively, on non-vested stock-settled awards and paid dividends of $1.5 and $1.2 for stock-settled awards that vested during 2018 and 2017, respectively.

A summary of the activity of our non-vested stock-settled awards, cash-settled awards and performance-based awards during 2018 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, 2018	2.1			$	22.78	0.1			$	22.52	8.3			$	21.05
Granted	2.1			23.60		0.1			23.62		2.9			21.13
Vested	(1.0		)	22.18		(0.1		)	21.54		(3.6		)	21.02
Forfeited	(0.1		)	23.67		0.0			23.17		(0.6		)	21.06
Non-vested as of December 31, 2018	3.1			$	23.51	0.1			$	23.47	7.0			$	21.10
Total unrecognized compensation expense remaining	$	39.4				$	1.0				$	54.7
Weighted-average years expected to be recognized over	1.6					1.3					1.7

In conjunction with our annual grant of long-term incentive compensation awards, we reviewed our estimates and assumptions in 2018, 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, 2018, 2017 and 2016, the Compensation Committee granted cash awards under the Cash Plan with a total target value of $20.9, $2.8 and $5.2, respectively. For those same years, we recognized $7.0, $2.5 and $3.1, respectively, in salaries and related expenses in our Consolidated Statements of Operations.

During the years ended December 31, 2018, 2017 and 2016, the Compensation Committee granted performance awards to be settled in cash under the 2014 PIP with a total target value of $39.9, $38.4, and $37.4, respectively. For those same years, we recognized $37.6, $35.3 and $39.8, 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 0.8 shares have been issued since the inception of the ESPP through December 31, 2018.

Fair Value Measurements (Notes)

12 Months Ended

Dec. 31, 2018

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 2018 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, 2018 and 2017, and indicates the fair value hierarchy of the valuation techniques utilized to determine such fair value.



	December 31, 2018								Balance Sheet Classification
	Level 1		Level 2		Level 3		Total		Balance Sheet Classification
Assets
Cash equivalents	$	132.1	$	0.0	$	0.0	$	132.1	Cash and cash equivalents

Liabilities
Contingent acquisition obligations ¹	$	0.0	$	0.0	$	148.4	$	148.4

	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

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 increase in this balance of $1.4 from December 31, 2017 to December 31, 2018 is primarily due to acquisitions and exercised put options of $61.8, partially offset by payments of $54.0. 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, 2018, and indicates the fair value hierarchy of the valuation techniques utilized to determine such fair value.



	December 31, 2018
	Level 1		Level 2		Level 3		Total
Total long-term debt	$	0.0	$	3,605.6	$	38.0	$	3,643.6

Our long-term debt is comprised of senior notes, a term loan 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 term loan is a fixed price commitment that cannot be traded on the open market, and therefore is 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 3 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.

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.

Commitments and Contingencies Disclosure [Abstract]

Employee Benefits (Notes)

12 Months Ended

Dec. 31, 2018

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 3,300 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 1,600 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.

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
	2018			2017			2018			2017			2018			2017
Benefit Obligation
Projected benefit obligation as of January 1	$	125.4		$	126.6		$	582.3		$	530.6		$	31.8		$	32.3
Service cost	0.0			0.0			5.4			4.9			0.0			0.0
Interest cost	4.5			5.1			13.1			13.5			1.1			1.3
Benefits paid	(9.5		)	(11.4		)	(27.4		)	(19.0		)	(5.9		)	(5.9		)
Plan participant contributions	0.0			0.0			0.1			0.2			1.8			1.6
Actuarial (gains) losses	(5.0		)	5.1			(47.6		)	20.3			(1.1		)	2.5
Settlements and curtailments	0.0			0.0			(5.8		)	(19.8		)	0.0			0.0
Foreign currency effect	0.0			0.0			(26.4		)	50.4			0.0			0.0
Other	0.0			0.0			2.3			1.2			0.0			0.0

Projected benefit obligation as of December 31	$	115.4		$	125.4		$	496.0		$	582.3		$	27.7		$	31.8

Fair Value of Plan Assets
Fair value of plan assets as of January 1	$	98.8		$	95.2		$	404.2		$	365.9		$	0.0		$	0.0
Actual return on plan assets	(8.1		)	12.4			(8.0		)	25.1			0.0			0.0
Employer contributions	8.6			2.6			19.1			17.5			4.1			4.3
Plan participant contributions	0.0			0.0			0.1			0.2			1.8			1.6
Benefits paid	(9.5		)	(11.4		)	(27.4		)	(19.0		)	(5.9		)	(5.9		)
Settlements	0.0			0.0			(4.6		)	(19.1		)	0.0			0.0
Foreign currency effect	0.0			0.0			(21.1		)	33.2			0.0			0.0
Other	0.0			0.0			1.6			0.4			0.0			0.0
																0.0
Fair value of plan assets as of December 31	$	89.8		$	98.8		$	363.9		$	404.2		$	0.0		$	0.0

Funded status of the plans at December 31	$	(25.6	)	$	(26.6	)	$	(132.1	)	$	(178.1	)	$	(27.7	)	$	(31.8	)



	Domestic Pension Plan						Foreign Pension Plans						Domestic Postretirement Benefit Plan
December 31,	2018			2017			2018			2017			2018			2017
Amounts recognized in Consolidated Balance Sheets
Non-current asset	$	0.0		$	0.0		$	8.6		$	9.0		$	0.0		$	0.0
Current liability	0.0			0.0			(6.2		)	(6.5		)	(2.9		)	(3.1		)
Non-current liability	(25.6		)	(26.6		)	(134.5		)	(180.6		)	(24.8		)	(28.7		)

Net liability recognized	$	(25.6	)	$	(26.6	)	$	(132.1	)	$	(178.1	)	$	(27.7	)	$	(31.8	)

Accumulated benefit obligation	$	115.4		$	125.4		$	493.2		$	577.9

Amounts recognized in Accumulated Other Comprehensive Loss, net
Net actuarial loss	$	60.4		$	52.2		$	165.6		$	201.6		$	3.1		$	4.2
Prior service cost (credit)	0.0			0.0			1.2			1.1			(0.3		)	(0.4		)

Total amount recognized	$	60.4		$	52.2		$	166.8		$	202.7		$	2.8		$	3.8

Actuarial gains of $5.0 for the Domestic Pension Plan are attributed to an increase in the discount rate from 3.70% as of December 31, 2017 to 4.35% as of December 31, 2018, partially offset by changes in demographic experience. Actuarial gains of $47.6 for the foreign pension plans are attributed to an increase in the weighted-average discount rate from 2.36% as of December 31, 2017 to 2.61% as of December 31, 2018 and changes in demographic experience.



	Domestic Pension Plan				Foreign Pension Plans
December 31,	2018		2017		2018		2017
Pension plans with an accumulated benefit obligation and projected benefit obligation in excess of plan assets
Aggregate projected benefit obligation	$	115.4	$	125.4	$	491.2	$	576.6
Aggregate accumulated benefit obligation	115.4		125.4		489.9		575.2
Aggregate fair value of plan assets	89.8		98.8		350.5		389.5

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,	2018			2017			2016			2018			2017			2016			2018			2017			2016
Service cost	$	0.0		$	0.0		$	0.0		$	5.4		$	4.9		$	6.7		$	0.0		$	0.0		$	0.0
Interest cost	4.5			5.1			5.9			13.1			13.5			15.1			1.1			1.3			1.5
Expected return on plan assets	(6.6		)	(6.2		)	(6.6		)	(18.8		)	(17.7		)	(18.7		)	0.0			0.0			0.0
Settlement and curtailment (gains) losses	0.0			0.0			0.0			(1.0		)	6.8			0.4			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		)	(0.2		)
Net actuarial losses	1.6			1.5			1.3			5.9			5.5			4.2			0.1			0.0			0.0
Net periodic cost	$	(0.5	)	$	0.4		$	0.6		$	4.7		$	13.1		$	7.8		$	1.0		$	1.1		$	1.3

Assumptions



	Domestic Pension Plan						Foreign Pension Plans						Domestic Postretirement Benefit Plan
Years ended December 31,	2018		2017		2016		2018		2017		2016		2018		2017		2016

Net periodic cost
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	%	3.18	%	N/A		N/A		N/A
Expected return on plan assets	7.00	%	7.00	%	7.00	%	4.70	%	4.66	%	5.38	%	N/A		N/A		N/A
Interest crediting rates	5.10	%	5.10	%	5.10	%	1.31	%	1.29	%	1.35	%	N/A		N/A		N/A

Benefit obligation
Discount rate	4.35	%	3.70	%	4.20	%	2.61	%	2.36	%	2.52	%	4.30	%	3.65	%	4.05	%
Rate of compensation increase	N/A		N/A		N/A		2.58	%	2.37	%	2.36	%	N/A		N/A		N/A
Interest crediting rates	5.10	%	5.10	%	5.10	%	1.44	%	1.31	%	1.29	%	N/A		N/A		N/A

Health care cost trend rate assumed for next year
Initial rate (weighted-average)													6.25	%	6.50	%	6.75	%
Year ultimate rate is reached													2024		2024		2024
Ultimate rate													5.00	%	5.00	%	5.00	%

Discount Rates – At December 31, 2018, 2017 and 2016, 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, 2018 and 2017, and indicates the fair value hierarchy of the valuation techniques utilized to determine such fair value. See Note 12 for a description of the fair value hierarchy.



	December 31, 2018								December 31, 2017
Plan assets subject to fair value hierarchy	Level 1		Level 2		Level 3		Total		Level 1		Level 2		Level 3		Total
Registered investment companies	$	13.0	$	0.0	$	0.0	$	13.0	$	14.7	$	0.0	$	0.0	$	14.7
Limited partnerships	0.0		0.0		25.6		25.6		0.0		0.0		29.5		29.5
Fixed income securities	23.1		0.0		0.0		23.1		23.4		0.0		0.0		23.4
Insurance contracts	0.0		5.8		0.0		5.8		0.0		7.9		0.0		7.9
Other	20.0		0.0		0.0		20.0		27.7		0.0		0.0		27.7
Total plan assets, subject to leveling	$	56.1	$	5.8	$	25.6	$	87.5	$	65.8	$	7.9	$	29.5	$	103.2
Plan assets measured at net asset value
Other investments measured at net asset value ¹							366.2								399.8
Total plan assets							$	453.7							$	503.0


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	2018			2017
Balance at beginning of period	$	29.5		$	28.0
Actual return on plan assets	(3.9		)	1.5
Balance at end of period	$	25.6		$	29.5

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, 2018, the weighted-average target and actual asset allocations relating to our domestic and foreign pension plans' assets are listed below.



			December 31,
Asset Class	2019 Target Allocation		2018		2017
Alternative investments ¹	26	%	26	%	27	%
Equity securities	23	%	22	%	23	%
Fixed income securities	21	%	21	%	21	%
Liability driven investments ²	16	%	16	%	14	%
Real estate	6	%	6	%	6	%
Other	8	%	9	%	9	%
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 2018, we contributed $8.6 and $19.1 of cash to our domestic and foreign pension plans, respectively. For 2019, we expect to contribute approximately $2.5 and $17.0 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
2019	$	14.5	$	21.7	$	3.0
2020	8.8		18.7		2.8
2021	8.0		19.8		2.6
2022	8.3		20.9		2.4
2023	7.8		21.8		2.2
2024 - 2028	36.7		117.2		9.8

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 2018, 2017 and 2016 were $52.6, $47.2 and $47.0, respectively. Expenses include a discretionary Company contribution of $6.7, $3.6 and $6.1 offset by participant forfeitures of $5.8, $4.6 and $4.4 in 2018, 2017 and 2016, respectively. In addition, we maintain defined contribution plans in various foreign countries and contributed $51.3, $47.4 and $44.5 to these plans in 2018, 2017 and 2016, respectively.

Deferred Compensation and Benefit Arrangements

We have deferred compensation and benefit 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. These arrangements may provide participants with the amounts deferred plus interest upon attaining certain conditions, such as completing a certain number of years of service, attaining a certain age or upon retirement or termination. As of December 31, 2018 and 2017, the deferred compensation and deferred benefit liability balance was $196.2 and $213.2, respectively. Amounts expensed for deferred compensation and benefit arrangements in 2018, 2017 and 2016 were $10.0, $18.5 and $18.5, 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, 2018 and 2017, the cash surrender value of these policies was $177.3 and $177.4, respectively.

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, 2018 and 2017. 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 $5.9 and $8.4 as of December 31, 2018 and 2017, respectively.

Segment Information (Notes)

12 Months Ended

Dec. 31, 2018

Segment Reporting [Abstract]

Segment Information

As of December 31, 2018, 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 range of solutions for our clients. Our digital specialist agencies provide digital capabilities and serve 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.

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.

Corporate and other is primarily comprised of selling, general and administrative expenses as well as three months of results from Acxiom in 2018. Selling, general and administrative expenses includes corporate office expenses as well as shared service center and certain other centrally managed expenses that are not fully allocated to operating divisions; salaries, long-term incentives, annual bonuses and other miscellaneous benefits for corporate office employees; professional fees related to internal control compliance, financial statement audits and legal, information technology and other consulting services that are engaged and managed through the corporate office; and rental expense for properties occupied by corporate office employees. A portion of centrally managed expenses is 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,
	2018			2017			2016
Total Revenue:
IAN	$	7,374.4		$	7,009.6		$	6,992.8
CMG	2,158.3			2,038.0			2,063.4
Corporate and other ¹	181.7			—			—
Total	$	9,714.4		$	9,047.6		$	9,056.2

Net revenue:
IAN	$	6,585.8		$	6,266.7		$	6,201.4
CMG	1,264.1			1,206.8			1,250.9
Corporate and other ¹	181.7			—			—
Total	$	8,031.6		$	7,473.5		$	7,452.3

Segment operating income (loss):
IAN	$	982.8		$	875.1		$	894.3
CMG	175.0			189.9			189.3
Corporate and other	(149.0		)	(126.6		)	(147.2		)
Total	1,008.8			938.4			936.4

Interest expense	(123.0		)	(90.8		)	(90.6		)
Interest income	21.8			19.4			20.1
Other expense, net	(69.6		)	(26.2		)	(40.3		)
Income before income taxes	$	838.0		$	840.8		$	825.6

Depreciation and amortization
IAN	$	142.8		$	125.5		$	129.2
CMG	24.3			23.5			22.4
Corporate and other	35.8			8.1			8.6
Total	$	202.9		$	157.1		$	160.2

Capital expenditures:
IAN	$	128.5		$	112.0		$	149.2
CMG	13.0			17.7			16.6
Corporate and other	35.6			26.2			34.9
Total	$	177.1		$	155.9		$	200.7



	December 31,
	2018		2017
Total assets:
IAN	$	11,446.2	$	10,978.0
CMG	1,516.7		1,427.4
Corporate and other ²	2,657.4		299.3
Total	$	15,620.3	$	12,704.7

¹ Revenue is from Acxiom which was acquired on October 1, 2018. See Note 6 for further detail on the acquisition.

² Includes $2,421.7 of assets held at Acxiom. See Note 6 for further detail on the acquisition.

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



	Net Revenue						Long-Lived Assets
	Years ended December 31,						December 31,
	2018		2017		2016		2018		2017
Domestic	$	4,825.0	$	4,458.8	$	4,443.2	$	892.9	$	694.5
International:
United Kingdom	711.7		613.1		604.3		57.9		56.2
Continental Europe	737.5		687.8		682.0		57.9		73.6
Asia Pacific	896.8		866.9		887.7		121.7		115.5
Latin America	350.1		350.8		367.8		43.6		48.2
Other	510.5		496.1		467.3		45.7		46.1
Total International	3,206.6		3,014.7		3,009.1		326.8		339.6
Total Consolidated	$	8,031.6	$	7,473.5	$	7,452.3	$	1,219.7	$	1,034.1

Net 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, 2018

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,
	2018			2017			2016
Gross rent expense	$	375.9		$	371.0		$	366.1
Third-party sublease rental income	(5.3		)	(4.6		)	(4.1		)
Net rent expense	$	370.6		$	366.4		$	362.0

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
2019	$	352.0	$	(7.7	)	$	344.3
2020	324.3		(5.2		)	319.1
2021	282.3		(2.2		)	280.1
2022	242.5		(1.3		)	241.2
2023	184.0		(0.6		)	183.4
Thereafter	714.6		(0.5		)	714.1
Total	$	2,099.7	$	(17.5	)	$	2,082.2

Guarantees

We have guaranteed certain obligations of our subsidiaries relating principally to operating leases and uncommitted lines of credit of certain subsidiaries. As of December 31, 2018 and 2017, the amount of parent company guarantees on lease obligations was $824.5 and $829.2, respectively, the amount of parent company guarantees primarily relating to uncommitted lines of credit was $349.1 and $308.8, respectively, and the amount of parent company guarantees related to daylight overdrafts, primarily utilized to manage intra-day overdrafts due to timing of transactions under cash pooling arrangements without resulting in incremental borrowings, was $207.8 and $182.2, 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, 2018, 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, 2018.



	2019		2020		2021		2022		2023		Thereafter		Total
Deferred acquisition payments	$	65.7	$	20.0	$	23.6	$	4.7	$	10.2	$	2.7	$	126.9
Redeemable noncontrolling interests and call options with affiliates ¹	30.1		30.6		42.9		5.7		3.5		2.5		115.3
Total contingent acquisition payments	$	95.8	$	50.6	$	66.5	$	10.4	$	13.7	$	5.2	$	242.2

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, 2018. These estimated payments of $24.9 are included within the total payments expected to be made in 2019, and will continue to be carried forward into 2020 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 5 for further information relating to the payment structure of our acquisitions.

Legal Matters

We are involved in various legal proceedings, and subject to investigations, inspections, audits, inquiries and similar actions by governmental authorities arising in the normal course of business. 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 has been in the process of concluding a settlement related to these matters with government agencies, and that settlement was fully executed in April 2018. The Company has previously provided for such settlement in its Consolidated Financial Statements.

In December 2016, one of the Company's standalone domestic agencies was contacted by the Department of Justice Antitrust Division (the "DOJ") for documents regarding video production practices. By letter dated November 5, 2018, the DOJ confirmed that the foregoing investigation has been closed, and all documents produced by the Company and its subsidiary were returned to the Company. The DOJ did not bring any charges against the Company or its subsidiary.

Recent Accounting Standards (Notes)	12 Months Ended
Recent Accounting Standards (Notes)	Dec. 31, 2018
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. Revenue Recognition See Notes 1 and 2 for further discussion on the adoption of ASC 606. Employee Benefits In August 2018, the Financial Accounting Standards Board (the "FASB") issued amended guidance that modifies the disclosure requirements for employers that sponsor defined benefit pension or other postretirement plans by removing disclosures that are no longer considered cost beneficial, clarifying requirements for certain disclosures, and adding disclosure requirements identified as relevant. The amended guidance is effective December 31, 2020, with early adoption permitted. We early adopted this amended guidance prospectively as of the quarter ended December 31, 2018. The adoption of this amended guidance did not have a significant impact on our Consolidated Financial Statements. Derivatives and Hedging In August 2017, 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 early adopted this amended guidance prospectively as of the quarter ended December 31, 2018, and applied the adoption as of January 1, 2018, as required. The adoption of this amended guidance did not have a significant impact on our Consolidated Financial Statements. 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 is effective beginning January 1, 2019, requires modified retrospective application, and allows for the application of the new guidance at the adoption date. We have made significant progress in implementing the system upgrades required to adopt the leasing standard, and are currently in the process of establishing appropriate controls and procedures surrounding the new guidance. As an accounting policy, we have elected not to apply the recognition requirements to short-term leases, not to separate non-lease components from lease components, and have elected the package of practical expedients as it relates to reassessment of existing leases as granted by the FASB. We do not expect the adoption of this amended guidance to have a significant impact on our Consolidated Statements of Operations, but will result in an estimated right-of-use asset and lease liability between $1,300.0 to $1,600.0 each on our Consolidated Balance Sheet effective January 1, 2019. Fair Value Measurements In January 2016, the FASB issued amended guidance that 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 was effective January 1, 2018. The adoption of this amended guidance did not have a significant impact on our Consolidated Financial Statements.

Results by Quarter (Unaudited) (Notes)

12 Months Ended

Dec. 31, 2018

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,
	2018			2017			2018			2017			2018			2017			2018			2017
Revenue:
Net revenue ^1,2	$	1,774.0		$	1,675.3		$	1,948.2		$	1,834.6		$	1,895.7		$	1,832.5		$	2,413.7		$	2,131.1
Billable expenses ^1,2	395.1			388.5			443.6			351.2			401.8			375.7			442.3			458.7
Total Revenue ^1,2	2,169.1			2,063.8			2,391.8			2,185.8			2,297.5			2,208.2			2,856.0			2,589.8

Operating Expenses:
Salaries and related expenses ²	1,330.3			1,251.7			1,292.9			1,228.9			1,251.4			1,218.8			1,423.7			1,291.3
Office and other direct ² expenses	323.8			312.7			333.3			318.4			317.0			302.9			381.0			334.8
Billable expenses ^1,2	395.1			388.5			443.6			351.2			401.8			375.7			442.3			458.7
Cost of services ²	2,049.2			1,952.9			2,069.8			1,898.5			1,970.2			1,897.4			2,247.0			2,084.8
Selling, general and administrative expenses ²	35.1			35.2			28.8			20.3			21.6			13.6			81.0			49.4
Depreciation and amortization ²	46.0			41.0			44.0			41.3			44.0			42.2			68.9			32.6
Total operating expenses ^1,2	2,130.3			2,029.1			2,142.6			1,960.1			2,035.8			1,953.2			2,396.9			2,166.8
Operating income ¹	38.8			34.7			249.2			225.7			261.7			255.0			459.1			423.0
Other (expense) income, net ³	(24.4		)	0.8			(16.3		)	(15.4		)	(15.3		)	(9.9		)	(13.6		)	(1.7		)
Total (expenses) and other income	(40.3		)	(14.9		)	(37.7		)	(36.4		)	(37.6		)	(26.8		)	(55.2		)	(19.5		)
Provision for (benefit of) income taxes^1,4	12.7			(0.3		)	63.6			81.6			60.7			54.9			62.2			135.1
Net (loss) income ¹	(16.1		)	21.3			147.8			107.6			163.5			172.3			342.5			269.2
Net (loss) income available to IPG common stockholders ¹	$	(14.1	)	$	24.7		$	145.8		$	107.7		$	161.0		$	169.7		$	326.2		$	252.3

(Loss) earnings per share available to IPG common stockholders:
Basic ¹	$	(0.04	)	$	0.06		$	0.38		$	0.27		$	0.42		$	0.44		$	0.85		$	0.66
Diluted ¹	$	(0.04	)	$	0.06		$	0.37		$	0.27		$	0.41		$	0.43		$	0.84		$	0.64

Dividends declared per common share	$	0.21		$	0.18		$	0.21		$	0.18		$	0.21		$	0.18		$	0.21		$	0.18


1	Effective January 1, 2018, the Company adopted Accounting Standards Codification Topic 606, Revenue from Contracts with Customers, ("ASC 606") using the full retrospective transition method and revised its Consolidated financial statements for the years ended December 31, 2017. See Note 1 and 2 for further detail on the ASC 606 adoption.

The Company has revised the presentation of its Consolidated Statements of Operations, which disaggregates net revenue and billable expenses within total revenue and separately presents cost of services; selling, general and administrative expenses; and depreciation and amortization within operating expenses. The revised presentation does not impact total revenue, total operating expenses or operating income.


3	The three months ended March 31, June 30, September 30 and December 31, 2018 included pre-tax net losses of $24.4, $19.8, $5.8, and $11.9, respectively, on sales of businesses. 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 December 31, 2018 included a tax benefit of $23.4 related to various discrete tax items. 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.

Significant Accounting Policies Principles of Consolidation (Policies)	12 Months Ended
	Dec. 31, 2018
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 recorded at cost, less any impairment, adjusted for subsequent observable price changes. 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, 2018
Accounting Policies [Abstract]
Reclassifications	Reclassifications As of January 1, 2018, the Company has revised the presentation of its Consolidated Statements of Operations, which disaggregates net revenue and billable expenses within total revenue and separately presents cost of services; selling, general and administrative expenses; and depreciation and amortization within operating expenses. The revised presentation does not impact total revenue, total operating expenses or operating income. Cost of services is comprised of the expenses of our revenue-producing operating segments including salaries and related expenses, office and other direct expenses and billable expenses, as well as an allocation of the centrally managed expenses from Corporate. Office and other direct expenses include rent expense, professional fees, certain expenses incurred by our staff in servicing our clients and other costs directly attributable to client engagements. Selling, general and administrative expenses are primarily the unallocated expenses from Corporate, as disclosed further in Note 14, excluding depreciation and amortization. Depreciation and amortization of the fixed assets and intangible assets of the Company is disclosed as a separate operating expense. Certain reclassifications and immaterial revisions have been made to prior-period financial statements to conform to the current-period presentation.

Significant Accounting Policies Use of Estimates (Policies)	12 Months Ended
	Dec. 31, 2018
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, 2018
Accounting Policies [Abstract]
Revenue Recognition	Revenue Recognition Our revenues are primarily derived from the planning and execution of multi-channel advertising and communications and marketing services, including public relations, meeting and event production, sports and entertainment marketing, corporate and brand identity, and strategic marketing consulting around the world. Most of our client contracts are individually negotiated and, accordingly, the terms of client engagements and the basis on which we earn fees and commissions vary significantly. Our contracts generally provide for termination by either party on relatively short notice, usually 30 to 90 days. Our payment terms vary by client, and the time between invoicing date and due date is typically not significant. We generally have the legally enforceable right to payment for all services provided through the end of the contract or termination date. Effective January 1, 2018, we adopted Accounting Standards Codification Topic 606, Revenue from Contracts with Customers, ("ASC 606") using the full retrospective transition method. Under this method, we revised our consolidated financial statements for the years ended December 31, 2016 and 2017, and applicable interim periods within the year ended December 31, 2017, as if ASC 606 had been effective for those periods. ASC 606 applies to all contracts with customers, except for contracts that are within the scope of other standards. We recognize revenue when we determine our customer obtains control of promised goods or services, in an amount that reflects the consideration which we expect to receive in exchange for those goods or services. To determine revenue recognition, we perform the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue as or when we satisfy the performance obligation. We only apply the five-step model to contracts when it is probable that IPG will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, we assess the goods or services promised within each contract and determine those that are distinct performance obligations. We then assess whether we act as an agent or a principal for each identified performance obligation and include revenue within the transaction price for third-party costs when we determine that we act as principal. We typically do not capitalize costs to obtain a contract as these amounts would generally be recognized over a period of one year or less. Net revenue, primarily consisting of fees, commissions and performance incentives, represents the amount of our gross billings excluding billable expenses charged to a client. Generally, our compensation is based on a negotiated fixed price, rate per hour, a retainer or commission. The majority of our fees are recognized over time as services are performed, utilizing a function of hours incurred and rates per hour, as compared to periodically updated estimates to complete. For certain less-frequent commission-based contracts which contain clauses allowing our clients to terminate the arrangement at any time for no compensation, revenue is recognized at a point in time, typically the date of broadcast or publication. We report revenue net of taxes assessed by governmental authorities that are directly imposed on our revenue-producing transactions. Contractual arrangements with clients may also include performance incentive provisions designed to link a portion of our revenue to our performance relative to mutually agreed-upon qualitative and/or quantitative metrics. Performance incentives are treated as variable consideration which is estimated at contract inception and included in revenue based on the most likely amount earned out of a range of potential outcomes. Our estimates are based on a combination of historical award experience, anticipated performance and our best judgment. These estimates are updated on a periodic basis and are not expected to result in a reversal of a significant amount of the cumulative revenue recognized. The predominant component of billable expenses are third-party vendor costs incurred for performance obligations where we have determined that we are acting as principal. These third-party expenses are generally billed back to our clients. Billable expenses also includes incidental costs incurred in the performance of our services including airfare, mileage, hotel stays, out-of-town meals and telecommunication charges. We record these billable expenses within total revenue with a corresponding offset to operating expenses. In international markets, we may receive rebates or credits from vendors based on transactions entered into on behalf of clients. Rebates and credits are remitted back to our clients in accordance with our contractual requirements or may be retained by us based on the terms of a particular client contract and local law. Amounts owed back to clients are recorded as a liability and amounts retained by us are recorded as revenue when earned. In certain international markets, our media contracts may allow clients to terminate our arrangement at any time for no compensation to the extent that media has not yet run. For those contracts, we do not recognize revenue until the media runs which is the point in time at which we have a legally enforceable right to compensation. Performance Obligations Our client contracts may include various goods and services that are capable of being distinct, are distinct within the context of the contract and are therefore accounted for as separate performance obligations. We allocate revenue to each performance obligation in the contract at inception based on its relative standalone selling price. Our advertising businesses include a wide range of services that involve the creation of an advertising idea, concept, campaign, or marketing strategy in order to promote the client’s brand ("creative services"), and to act as an agent to facilitate the production of advertisements by third-party suppliers ("production services”). Our clients can contract us to perform one or both of these services, as they can derive stand-alone benefit from each. Production services can include formatting creative material for different media and communication mediums including digital, large-scale reproduction such as printing and adaptation services, talent engagement and acquisition, television and radio production, and outdoor billboard production. Our contracts that include both services are typically explicit in the description of which activities constitute the creative advertising services and those that constitute the production services. Both the creative and production services are sold separately, the client can derive utility from each service on its own, we do not provide a significant service of integrating these activities into a bundle, the services do not significantly modify one another, and the services are not highly interrelated or interdependent. As such, we typically identify two performance obligations in the assessment of our advertising contracts. Our media businesses include services to formulate strategic media plans ("media planning services") and to act as an agent to purchase media (e.g. television and radio spots, outdoor advertising, digital banners, etc.) from vendors on their behalf ("media buying services"). Our contracts that include both services are typically explicit in the description of which activities constitute the planning services and those that constitute the buying services. Both the planning and buying services are sold separately, the client can derive utility from each service on its own, we do not provide a significant service of integrating these activities into a bundle, the services do not significantly modify one another, and the services are not highly interrelated or interdependent. As such, we typically identify two performance obligations in the assessment of our media contracts. Our events businesses include creative services related to the conception and planning of custom marketing events as well as activation services which entail the carrying out of the event, including, but not limited to, set-up, design and staffing. Additionally, our public relations businesses include a broad range of services, such as strategic planning, social media strategy and the monitoring and development of communication strategies, among others. While our contracts in these businesses may include some or all of these services, we typically identify only one performance obligation in the assessment of our events and public relations contracts as we provide a significant service of integrating the individual services into a combined service for which the customer has contracted. As part of our adoption of ASC 606, we elected not to disclose information about remaining performance obligations that have original expected durations of one year or less. The majority of our contracts are for periods of one-year or less. For those contracts with a term of more than one year, we had approximately $770.0 of unsatisfied performance obligations as of December 31, 2018 which will be recognized as services are performed over the remaining contractual terms. Principal vs. Agent When a third-party is involved in the delivery of our services to the client, we assess whether or not we are acting as a principal or an agent in the arrangement. The assessment is based on whether we control the specified services at any time before they are transferred to the customer. We have determined that in our events and public relations businesses, we generally act as a principal as our agencies provide a significant service of integrating goods or services provided by third parties into the specified deliverable to our clients. In addition, we have determined that we are responsible for the performance of the third-party suppliers, which are combined with our own services, before transferring those services to the customer. In addition, we have determined that we act as principal when providing creative services and media planning services, as we perform a significant integration service in these transactions. For performance obligations in which we act as principal, we record the gross amount billed to the customer within total revenue and the related incremental direct costs incurred as billable expenses. When a third-party is involved in the production of an advertising campaign and for media buying services, we have determined that we act as the agent and are solely arranging for the third-party to provide services to the customer. Specifically, we do not control the specified services before transferring those services to the customer, we are not primarily responsible for the performance of the third-party services, nor can we redirect those services to fulfill any other contracts. We do not have inventory risk or discretion in establishing pricing in our contracts with customers. For performance obligations for which we act as the agent, we record our revenue as the net amount of our gross billings less amounts remitted to third parties.

Significant Accounting Policies Cash and Cash Equivalents (Policies)	12 Months Ended
	Dec. 31, 2018
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, 2018
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.

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.

Significant Accounting Policies Investments (Policies)	12 Months Ended
Significant Accounting Policies Investments (Policies)	Dec. 31, 2018
Accounting Policies [Abstract]
Investments	Investments Our non-publicly traded investments and all other publicly traded investments are accounted for using the equity method or are recorded at fair value. We regularly review our investments to determine whether a significant event or change in circumstances has occurred that may impact the fair value of each investment, with changes to fair value recorded in earnings. 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 a decline in value of an investment has occurred.

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.

Significant Accounting Policies Derivatives (Policies)	12 Months Ended
Significant Accounting Policies Derivatives (Policies)	Dec. 31, 2018
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 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, 2018
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, 2018
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 13 reporting units that were subject to the 2018 annual impairment testing. Our annual impairment review as of October 1, 2018 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 2018 and 2017 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 asset groups. These asset groups 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, 2018
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 $5.6, $1.9 and $2.1 in for the years ended December 31, 2018, 2017 and 2016, 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, 2018
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. Public Law 115-97, commonly referred to as the Tax Cuts and Jobs Act (the "Tax Act") was signed into law on December 22, 2017. The Tax Act legislated many new tax provisions which have impacted our operations. At December 31, 2017, provisional amounts were recorded as permitted by SEC Staff issued Accounting Bulletin No. 118 (“SAB 118”). We have finalized our calculations of the impact of the Tax Act and have revised our estimates as required by SAB 118. See Note 9 for further information.

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.

Significant Accounting Policies Redeemable Noncontrolling Interests (Policies)	12 Months Ended
	Dec. 31, 2018
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, 2018
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, 2018, 2017 and 2016, 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, 2018
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.

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.

Revenue from Contract with Customer [Abstract]

Revenue (Tables)

12 Months Ended

Dec. 31, 2018

Condensed Income Statement [Table Text Block]

CONSOLIDATED STATEMENT OF OPERATIONS



	Year ended December 31, 2017									Year ended December 31, 2016
	As Revised ¹			ASC 606 Adjustments			As Adjusted			As Revised ¹			ASC 606 Adjustments			As Adjusted
REVENUE:
Net revenue	$	7,508.7		$	(35.2	)	$	7,473.5		$	7,456.9		$	(4.6	)	$	7,452.3
Billable expenses	373.7			1,200.4			1,574.1			389.7			1,214.2			1,603.9
Total revenue	7,882.4			1,165.2			9,047.6			7,846.6			1,209.6			9,056.2

OPERATING EXPENSES:
Salaries and related expenses	4,990.7			—			4,990.7			4,942.2			—			4,942.2
Office and other direct expenses	1,268.8			—			1,268.8			1,274.9			—			1,274.9
Billable expenses	373.7			1,200.4			1,574.1			389.7			1,214.2			1,603.9
Cost of services	6,633.2			1,200.4			7,833.6			6,606.8			1,214.2			7,821.0
Selling, general and administrative expenses	118.5			—			118.5			138.6			—			138.6
Depreciation and amortization	157.1			—			157.1			160.2			—			160.2
Total operating expenses	6,908.8			1,200.4			8,109.2			6,905.6			1,214.2			8,119.8

OPERATING INCOME	973.6			(35.2		)	938.4			941.0			(4.6		)	936.4

EXPENSES AND OTHER INCOME:
Interest expense	(90.8		)	—			(90.8		)	(90.6		)	—			(90.6		)
Interest income	19.4			—			19.4			20.1			—			20.1
Other expense, net	(26.2		)	—			(26.2		)	(40.3		)	—			(40.3		)
Total (expenses) and other income	(97.6		)	—			(97.6		)	(110.8		)	—			(110.8		)

Income before income taxes	876.0			(35.2		)	840.8			830.2			(4.6		)	825.6
Provision for income taxes	281.9			(10.6		)	271.3			198.0			(1.1		)	196.9
Income of consolidated companies	594.1			(24.6		)	569.5			632.2			(3.5		)	628.7
Equity in net income of unconsolidated affiliates	0.9			—			0.9			0.3			—			0.3
NET INCOME	595.0			(24.6		)	570.4			632.5			(3.5		)	629.0
Net income attributable to noncontrolling interests	(16.0		)	—			(16.0		)	(24.0		)	—			(24.0		)
NET INCOME AVAILABLE TO IPG COMMON STOCKHOLDERS	$	579.0		$	(24.6	)	$	554.4		$	608.5		$	(3.5	)	$	605.0

Earnings per share available to IPG common stockholders:
Basic	$	1.49		$	(0.07	)	$	1.42		$	1.53		$	(0.01	)	$	1.52
Diluted	$	1.46		$	(0.06	)	$	1.40		$	1.49		$	(0.01	)	$	1.48

Weighted-average number of common shares outstanding:
Basic	389.6			—			389.6			397.9			—			397.9
Diluted	397.3			—			397.3			408.0			—			408.0


1	These amounts have been revised for the new presentation as described in Note 1.

Condensed Cash Flow Statement [Table Text Block]

CONSOLIDATED STATEMENT OF CASH FLOWS



	Year ended December 31, 2017
	As Reported			ASC 606 Adjustments			As Adjusted
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$	595.0		$	(24.6	)	$	570.4
Adjustments to reconcile net income to net cash used in operating activities:
Depreciation and amortization	157.1			—			157.1
Provision for uncollectible receivables	9.5			—			9.5
Amortization of restricted stock and other non-cash compensation	82.0			—			82.0
Net amortization of bond discounts and deferred financing costs	5.8			—			5.8
Deferred income tax provision	1.1			(10.6		)	(9.5		)
Net losses on sales of businesses	24.1			—			24.1
Other	12.7			—			12.7
Changes in assets and liabilities, net of acquisitions and divestitures, providing (using) cash:
Accounts receivable	37.6			—			37.6
Expenditures billable to clients	(165.5		)	165.5			—
Accounts receivable, billable to clients	—			(165.5		)	(165.5		)
Other current assets	27.4			22.7			50.1
Accounts payable	311.9			24.5			336.4
Accrued liabilities	(241.3		)	—			(241.3		)
Contract liabilities	—			(12.0		)	(12.0		)
Other non-current assets and liabilities	24.4			—			24.4
Net cash provided by operating activities	881.8			—			881.8
CASH FLOWS FROM INVESTING ACTIVITIES:
Net cash used in investing activities	(196.2		)	—			(196.2		)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net cash used in financing activities	(1,004.9		)	—			(1,004.9		)
Effect of foreign exchange rate changes on cash, cash equivalents and restricted cash	16.8			—			16.8
Net decrease in cash, cash equivalents and restricted cash	(302.5		)	—			(302.5		)
Cash, cash equivalents and restricted cash at beginning of period	1,100.2			—			1,100.2
Cash, cash equivalents and restricted cash at end of period	$	797.7		$	—		$	797.7



	Year ended December 31, 2016
	As Reported			ASC 606 Adjustments			As Adjusted
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$	632.5		$	(3.5	)	$	629.0
Adjustments to reconcile net income to net cash used in operating activities:
Depreciation and amortization	160.2			—			160.2
Provision for uncollectible receivables	16.7			—			16.7
Amortization of restricted stock and other non-cash compensation	85.6			—			85.6
Net amortization of bond discounts and deferred financing costs	5.6			—			5.6
Deferred income tax provision	45.7			(1.1		)	44.6
Net losses on sales of businesses	41.4			—			41.4
Other	35.5			—			35.5
Changes in assets and liabilities, net of acquisitions and divestitures, providing (using) cash:
Accounts receivable	(220.7		)	—			(220.7		)
Expenditures billable to clients	(2.2		)	2.2			—
Accounts receivable, billable to clients	—			(2.2		)	(2.2		)
Other current assets	(4.8		)	5.3			0.5
Accounts payable	(126.1		)	(21.3		)	(147.4		)
Accrued liabilities	(61.1		)	—			(61.1		)
Contract liabilities	—			20.6			20.6
Other non-current assets and liabilities	(95.5		)	—			(95.5		)
Net cash provided by operating activities	512.8			—			512.8
CASH FLOWS FROM INVESTING ACTIVITIES:
Net cash used in investing activities	(263.9		)	—			(263.9		)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net cash used in financing activities	(666.4		)	—			(666.4		)
Effect of foreign exchange rate changes on cash, cash equivalents and restricted cash	11.6			—			11.6
Net decrease in cash, cash equivalents and restricted cash	(405.9		)	—			(405.9		)
Cash, cash equivalents and restricted cash at beginning of period	1,506.1			—			1,506.1
Cash, cash equivalents and restricted cash at end of period	$	1,100.2		$	—		$	1,100.2

Condensed Balance Sheet [Table Text Block]

CONSOLIDATED BALANCE SHEET



	December 31, 2017
	As Reported			ASC 606 Adjustments			As Adjusted
ASSETS:
Cash and cash equivalents	$	790.9		$	—		$	790.9
Accounts receivable, net of allowance of $42.7	4,585.0			—			4,585.0
Expenditures billable to clients	1,747.4			(1,747.4		)	—
Accounts receivable, billable to clients	—			1,747.4			1,747.4
Assets held for sale	5.7			—			5.7
Other current assets	335.1			11.4			346.5
Total current assets	7,464.1			11.4			7,475.5
Property and equipment, net of accumulated depreciation of $1,036.2	650.4			—			650.4
Deferred income taxes	236.0			(2.0		)	234.0
Goodwill	3,820.4			—			3,820.4
Other intangible assets	140.7			—			140.7
Other non-current assets	383.6			0.1			383.7
TOTAL ASSETS	$	12,695.2		$	9.5		$	12,704.7

LIABILITIES:
Accounts payable	$	6,907.8		$	(487.6	)	$	6,420.2
Accrued liabilities	674.7			—			674.7
Contract liabilities	—			484.7			484.7
Short-term borrowings	84.9			—			84.9
Current portion of long-term debt	2.0			—			2.0
Liabilities held for sale	8.8			—			8.8
Total current liabilities	7,678.2			(2.9		)	7,675.3
Long-term debt	1,285.6			—			1,285.6
Deferred compensation	476.6			—			476.6
Other non-current liabilities	766.9			1.9			768.8
TOTAL LIABILITIES	10,207.3			(1.0		)	10,206.3

Redeemable noncontrolling interests	252.1			—			252.1

STOCKHOLDERS’ EQUITY:
Common stock	38.6			—			38.6
Additional paid-in capital	955.2			—			955.2
Retained earnings	2,093.6			10.9			2,104.5
Accumulated other comprehensive loss, net of tax	(827.4		)	(0.4		)	(827.8		)
	2,260.0			10.5			2,270.5
Less: Treasury stock	(59.0		)	—			(59.0		)
Total IPG stockholders’ equity	2,201.0			10.5			2,211.5
Noncontrolling interests	34.8			—			34.8
TOTAL STOCKHOLDERS’ EQUITY	2,235.8			10.5			2,246.3
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$	12,695.2		$	9.5		$	12,704.7

Revenue from External Customers by Geographic Areas [Table Text Block]



	Years ended December 31,
Total revenue:	2018		2017		2016
United States	$	5,851.0	$	5,417.3	$	5,452.6
International:
United Kingdom	881.4		775.7		788.8
Continental Europe	840.2		780.6		764.1
Asia Pacific	1,170.8		1,106.4		1,076.0
Latin America	389.0		386.6		417.2
Other	582.0		581.0		557.5
Total International	3,863.4		3,630.3		3,603.6
Total Consolidated	$	9,714.4	$	9,047.6	$	9,056.2



	Years ended December 31,
Net revenue:	2018		2017		2016
United States	$	4,825.0	$	4,458.8	$	4,443.2
International:
United Kingdom	711.7		613.1		604.3
Continental Europe	737.5		687.8		682.0
Asia Pacific	896.8		866.9		887.7
Latin America	350.1		350.8		367.8
Other	510.5		496.1		467.3
Total International	3,206.6		3,014.7		3,009.1
Total Consolidated	$	8,031.6	$	7,473.5	$	7,452.3



IAN	Years ended December 31,
Total revenue:	2018		2017		2016
United States	$	4,279.4	$	4,062.3	$	4,075.9
International	3,095.0		2,947.3		2,916.9
Total IAN	$	7,374.4	$	7,009.6	$	6,992.8

Net revenue:
United States	$	3,832.7	$	3,660.6	$	3,600.3
International	2,753.1		2,606.1		2,601.1
Total IAN	$	6,585.8	$	6,266.7	$	6,201.4



CMG	Years ended December 31,
Total revenue:	2018		2017		2016
United States	$	1,404.0	$	1,355.0	$	1,376.7
International	754.3		683.0		686.7
Total CMG	$	2,158.3	$	2,038.0	$	2,063.4

Net revenue:
United States	$	824.6	$	798.2	$	842.9
International	439.5		408.6		408.0
Total CMG	$	1,264.1	$	1,206.8	$	1,250.9

Contract with Customer, Asset and Liability [Table Text Block]

Contract Balances

The following table provides information about receivables, contract assets and contract liabilities from contracts with customers.



	December 31, 2018		December 31, 2017
Accounts receivable, net of allowance of $42.5 and $42.7, respectively	$	5,126.6	$	4,585.0
Accounts receivable, billable to clients	1,900.6		1,747.4
Contract assets	67.9		11.5
Contract liabilities (deferred revenue)	533.9		484.7

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

12 Months Ended

Dec. 31, 2018

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,
			2018				2017
			Book Value		Fair Value ¹		Book Value		Fair Value ¹
3.50% Senior Notes due 2020 (less unamortized discount and issuance costs of $0.8 and $2.6, respectively)	3.89	%	$	496.6	$	499.9	$	—	$	—
3.75% Senior Notes due 2021 (less unamortized discount and issuance costs of $0.3 and $2.9, respectively)	3.98	%	496.8		503.2		—		—
4.00% Senior Notes due 2022 (less unamortized discount and issuance costs of $1.0 and $0.8, respectively)	4.13	%	248.2		250.3		247.6		259.0
3.75% Senior Notes due 2023 (less unamortized discount and issuance costs of $0.6 and $1.7, respectively)	4.32	%	497.7		491.4		497.1		513.2
4.20% Senior Notes due 2024 (less unamortized discount and issuance costs of $0.5 and $2.2, respectively)	4.24	%	497.3		492.6		496.7		524.2
4.65% Senior Notes due 2028 (less unamortized discount and issuance costs of $1.7 and $4.3, respectively)	4.78	%	494.0		494.1		—		—
5.40% Senior Notes due 2048 (less unamortized discount and issuance costs of $2.8 and $5.5, respectively)	5.48	%	491.7		474.1		—		—
Term Loan due 2021 - LIBOR plus 1.25%			400.0		400.0		—
Other notes payable and capitalized leases			38.0		38.0		46.2		46.2
Total long-term debt			3,660.3				1,287.6
Less: current portion			0.1				2.0
Long-term debt, excluding current portion			$	3,660.2			$	1,285.6


1	See Note 12 for information on the fair value measurement of our long-term debt.

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://fasb.org/us-gaap/role/ref/legacyRef
-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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28541-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21506-112644

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21521-112644

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21538-112644

Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
-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 9: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644

+ Details

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

12 Months Ended

Dec. 31, 2018

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,
	2018			2017			2016
Cost of investment: current-year acquisitions ¹	$	2,323.4		$	36.8		$	65.7
Cost of investment: prior-year acquisitions	33.9			54.6			40.7
Less: net cash acquired	(13.8		)	(7.1		)	(13.6		)
Total cost of investment	2,343.5			84.3			92.8
Operating payments²	19.4			47.1			19.1
Total cash paid for acquisitions ³	$	2,362.9		$	131.4		$	111.9


1	The cost of investment: current-year acquisitions line significantly increased in the year ended December 31, 2018, primarily as a result of payments related to the acquisition of Acxiom. See Note 6 for further information on the Acxiom Acquisition.

Acxiom Acquisition (Tables)

12 Months Ended

Dec. 31, 2018

Preliminary fair values of the assets acquired and liabilities assumed Table



	October 1, 2018
Cash and cash equivalents	$	13.3
Accounts receivable	112.9
Accounts receivable, billable to clients	8.3
Other current assets	28.2
Property and equipment, net	159.7
Deferred income taxes	(0.6		)
Goodwill	1,110.8
Intangible assets, net	995.0
Other non-current assets	8.3
Accounts payable	(37.1		)
Accrued liabilities	(46.9		)
Contract liabilities	(23.2		)
Other non-current liabilities	(0.8		)
Net assets acquired	$	2,327.9

Preliminary fair values of the identifiable intangible assets acquired at the closing date Table



	Fair Value		Weighted Average Amortization Period (Years)
Customer lists	$	600.0	15.0
Know-how and technology	235.0		9.0
Trade names	160.0		15.0 to indefinite
Total intangible assets	995.0

Acxiom pro forma Table



	(unaudited)
	December 31,
	2018		2017
Pro forma revenues	$	10,230.4	$	9,736.1
Pro forma net income	642.2		519.2

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

12 Months Ended

Dec. 31, 2018

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,
	2018			2017			2016
U.S. federal income taxes (including foreign withholding taxes):
Current	$	38.1		$	154.1		$	54.3
Deferred	29.9			(37.6		)	35.7
	68.0			116.5			90.0
State and local income taxes:
Current	25.1			18.8			8.2
Deferred	3.4			19.7			(1.6		)
	28.5			38.5			6.6
Foreign income taxes:
Current	121.9			107.9			89.8
Deferred	(19.2		)	8.4			10.5
	102.7			116.3			100.3
Total	$	199.2		$	271.3		$	196.9

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

12 Months Ended

Dec. 31, 2018

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,
	2018			2017			2016
U.S. federal statutory income tax rate	21.0		%	35.0		%	35.0		%

Income tax provision at U.S. federal statutory rate	$	176.0		$	294.3		$	289.0
State and local income taxes, net of U.S. federal income tax benefit	23.8			23.5			4.3
Impact of foreign operations, including withholding taxes	50.7			(6.7		)	(23.9		)
U.S. tax incentives	(17.5		)	(1.3		)	(1.3		)
Change in net valuation allowance ¹	(16.9		)	1.4			(13.4		)
Divestitures	11.7			1.1			9.7
U.S. federal tax credits	(48.1		)	(0.4		)	(44.6		)
Stock compensation	(6.8		)	(15.3		)	(9.0		)
Increase/(decrease) in unrecognized tax benefits	8.4			7.0			(21.8		)
Net impact of the Tax Act	13.4			(36.0		)	0.0
Statutory tax rate changes	0.0			0.0			11.4
Other	4.5			3.7			(3.5		)
Provision for income taxes	$	199.2		$	271.3		$	196.9

Effective income tax rate on operations	23.8		%	32.3		%	23.8		%


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

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

12 Months Ended

Dec. 31, 2018

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, 2018 and 2017.



	Years ended December 31,
	2018		2017		2016
Stock-Settled Awards:
Awards granted	2.1		0.8		1.1
Weighted-average grant-date fair value (per award)	$	23.60	$	24.18	$	21.87
Total fair value of vested awards distributed	$	24.2	$	22.6	$	17.5
Cash-Settled Awards:
Awards granted	0.1		0.0		0.1
Weighted-average grant-date fair value (per award)	$	23.62	$	23.33	$	22.54
Total fair value of vested awards distributed	$	0.8	$	0.9	$	0.7
Performance-Based Awards:
Awards granted	2.9		4.8		3.3
Weighted-average grant-date fair value (per award)	$	21.13	$	20.06	$	19.58
Total fair value of vested awards distributed	$	87.2	$	112.4	$	27.9

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

12 Months Ended

Dec. 31, 2018

Fair Value Disclosures [Abstract]

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



	December 31, 2018								Balance Sheet Classification
	Level 1		Level 2		Level 3		Total		Balance Sheet Classification
Assets
Cash equivalents	$	132.1	$	0.0	$	0.0	$	132.1	Cash and cash equivalents

Liabilities
Contingent acquisition obligations ¹	$	0.0	$	0.0	$	148.4	$	148.4

	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

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

12 Months Ended

Dec. 31, 2018

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

Fair Value Measurements, Nonrecurring [Table Text Block]



	December 31, 2018
	Level 1		Level 2		Level 3		Total
Total long-term debt	$	0.0	$	3,605.6	$	38.0	$	3,643.6

Schedule of Defined Benefit Plans Disclosures (Tables)

12 Months Ended

Dec. 31, 2018

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
	2018			2017			2018			2017			2018			2017
Benefit Obligation
Projected benefit obligation as of January 1	$	125.4		$	126.6		$	582.3		$	530.6		$	31.8		$	32.3
Service cost	0.0			0.0			5.4			4.9			0.0			0.0
Interest cost	4.5			5.1			13.1			13.5			1.1			1.3
Benefits paid	(9.5		)	(11.4		)	(27.4		)	(19.0		)	(5.9		)	(5.9		)
Plan participant contributions	0.0			0.0			0.1			0.2			1.8			1.6
Actuarial (gains) losses	(5.0		)	5.1			(47.6		)	20.3			(1.1		)	2.5
Settlements and curtailments	0.0			0.0			(5.8		)	(19.8		)	0.0			0.0
Foreign currency effect	0.0			0.0			(26.4		)	50.4			0.0			0.0
Other	0.0			0.0			2.3			1.2			0.0			0.0

Projected benefit obligation as of December 31	$	115.4		$	125.4		$	496.0		$	582.3		$	27.7		$	31.8

Fair Value of Plan Assets
Fair value of plan assets as of January 1	$	98.8		$	95.2		$	404.2		$	365.9		$	0.0		$	0.0
Actual return on plan assets	(8.1		)	12.4			(8.0		)	25.1			0.0			0.0
Employer contributions	8.6			2.6			19.1			17.5			4.1			4.3
Plan participant contributions	0.0			0.0			0.1			0.2			1.8			1.6
Benefits paid	(9.5		)	(11.4		)	(27.4		)	(19.0		)	(5.9		)	(5.9		)
Settlements	0.0			0.0			(4.6		)	(19.1		)	0.0			0.0
Foreign currency effect	0.0			0.0			(21.1		)	33.2			0.0			0.0
Other	0.0			0.0			1.6			0.4			0.0			0.0
																0.0
Fair value of plan assets as of December 31	$	89.8		$	98.8		$	363.9		$	404.2		$	0.0		$	0.0

Funded status of the plans at December 31	$	(25.6	)	$	(26.6	)	$	(132.1	)	$	(178.1	)	$	(27.7	)	$	(31.8	)



	Domestic Pension Plan						Foreign Pension Plans						Domestic Postretirement Benefit Plan
December 31,	2018			2017			2018			2017			2018			2017
Amounts recognized in Consolidated Balance Sheets
Non-current asset	$	0.0		$	0.0		$	8.6		$	9.0		$	0.0		$	0.0
Current liability	0.0			0.0			(6.2		)	(6.5		)	(2.9		)	(3.1		)
Non-current liability	(25.6		)	(26.6		)	(134.5		)	(180.6		)	(24.8		)	(28.7		)

Net liability recognized	$	(25.6	)	$	(26.6	)	$	(132.1	)	$	(178.1	)	$	(27.7	)	$	(31.8	)

Accumulated benefit obligation	$	115.4		$	125.4		$	493.2		$	577.9

Amounts recognized in Accumulated Other Comprehensive Loss, net
Net actuarial loss	$	60.4		$	52.2		$	165.6		$	201.6		$	3.1		$	4.2
Prior service cost (credit)	0.0			0.0			1.2			1.1			(0.3		)	(0.4		)

Total amount recognized	$	60.4		$	52.2		$	166.8		$	202.7		$	2.8		$	3.8



	Domestic Pension Plan				Foreign Pension Plans
December 31,	2018		2017		2018		2017
Pension plans with an accumulated benefit obligation and projected benefit obligation in excess of plan assets
Aggregate projected benefit obligation	$	115.4	$	125.4	$	491.2	$	576.6
Aggregate accumulated benefit obligation	115.4		125.4		489.9		575.2
Aggregate fair value of plan assets	89.8		98.8		350.5		389.5

Employee Benefits Schedule of Net Benefit Costs (Tables)

12 Months Ended

Dec. 31, 2018

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,	2018			2017			2016			2018			2017			2016			2018			2017			2016
Service cost	$	0.0		$	0.0		$	0.0		$	5.4		$	4.9		$	6.7		$	0.0		$	0.0		$	0.0
Interest cost	4.5			5.1			5.9			13.1			13.5			15.1			1.1			1.3			1.5
Expected return on plan assets	(6.6		)	(6.2		)	(6.6		)	(18.8		)	(17.7		)	(18.7		)	0.0			0.0			0.0
Settlement and curtailment (gains) losses	0.0			0.0			0.0			(1.0		)	6.8			0.4			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		)	(0.2		)
Net actuarial losses	1.6			1.5			1.3			5.9			5.5			4.2			0.1			0.0			0.0
Net periodic cost	$	(0.5	)	$	0.4		$	0.6		$	4.7		$	13.1		$	7.8		$	1.0		$	1.1		$	1.3

Assumptions



	Domestic Pension Plan						Foreign Pension Plans						Domestic Postretirement Benefit Plan
Years ended December 31,	2018		2017		2016		2018		2017		2016		2018		2017		2016

Net periodic cost
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	%	3.18	%	N/A		N/A		N/A
Expected return on plan assets	7.00	%	7.00	%	7.00	%	4.70	%	4.66	%	5.38	%	N/A		N/A		N/A
Interest crediting rates	5.10	%	5.10	%	5.10	%	1.31	%	1.29	%	1.35	%	N/A		N/A		N/A

Benefit obligation
Discount rate	4.35	%	3.70	%	4.20	%	2.61	%	2.36	%	2.52	%	4.30	%	3.65	%	4.05	%
Rate of compensation increase	N/A		N/A		N/A		2.58	%	2.37	%	2.36	%	N/A		N/A		N/A
Interest crediting rates	5.10	%	5.10	%	5.10	%	1.44	%	1.31	%	1.29	%	N/A		N/A		N/A

Health care cost trend rate assumed for next year
Initial rate (weighted-average)													6.25	%	6.50	%	6.75	%
Year ultimate rate is reached													2024		2024		2024
Ultimate rate													5.00	%	5.00	%	5.00	%

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

12 Months Ended

Dec. 31, 2018

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,
	2018			2017			2016
Total Revenue:
IAN	$	7,374.4		$	7,009.6		$	6,992.8
CMG	2,158.3			2,038.0			2,063.4
Corporate and other ¹	181.7			—			—
Total	$	9,714.4		$	9,047.6		$	9,056.2

Net revenue:
IAN	$	6,585.8		$	6,266.7		$	6,201.4
CMG	1,264.1			1,206.8			1,250.9
Corporate and other ¹	181.7			—			—
Total	$	8,031.6		$	7,473.5		$	7,452.3

Segment operating income (loss):
IAN	$	982.8		$	875.1		$	894.3
CMG	175.0			189.9			189.3
Corporate and other	(149.0		)	(126.6		)	(147.2		)
Total	1,008.8			938.4			936.4

Interest expense	(123.0		)	(90.8		)	(90.6		)
Interest income	21.8			19.4			20.1
Other expense, net	(69.6		)	(26.2		)	(40.3		)
Income before income taxes	$	838.0		$	840.8		$	825.6

Depreciation and amortization
IAN	$	142.8		$	125.5		$	129.2
CMG	24.3			23.5			22.4
Corporate and other	35.8			8.1			8.6
Total	$	202.9		$	157.1		$	160.2

Capital expenditures:
IAN	$	128.5		$	112.0		$	149.2
CMG	13.0			17.7			16.6
Corporate and other	35.6			26.2			34.9
Total	$	177.1		$	155.9		$	200.7



	December 31,
	2018		2017
Total assets:
IAN	$	11,446.2	$	10,978.0
CMG	1,516.7		1,427.4
Corporate and other ²	2,657.4		299.3
Total	$	15,620.3	$	12,704.7

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

12 Months Ended

Dec. 31, 2018

Segment Reporting [Abstract]

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

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



	Net Revenue						Long-Lived Assets
	Years ended December 31,						December 31,
	2018		2017		2016		2018		2017
Domestic	$	4,825.0	$	4,458.8	$	4,443.2	$	892.9	$	694.5
International:
United Kingdom	711.7		613.1		604.3		57.9		56.2
Continental Europe	737.5		687.8		682.0		57.9		73.6
Asia Pacific	896.8		866.9		887.7		121.7		115.5
Latin America	350.1		350.8		367.8		43.6		48.2
Other	510.5		496.1		467.3		45.7		46.1
Total International	3,206.6		3,014.7		3,009.1		326.8		339.6
Total Consolidated	$	8,031.6	$	7,473.5	$	7,452.3	$	1,219.7	$	1,034.1

Commitments and Contingencies Schedule of Contingent Acquisition Obligations (Tables)

12 Months Ended

Dec. 31, 2018

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, 2018.



	2019		2020		2021		2022		2023		Thereafter		Total
Deferred acquisition payments	$	65.7	$	20.0	$	23.6	$	4.7	$	10.2	$	2.7	$	126.9
Redeemable noncontrolling interests and call options with affiliates ¹	30.1		30.6		42.9		5.7		3.5		2.5		115.3
Total contingent acquisition payments	$	95.8	$	50.6	$	66.5	$	10.4	$	13.7	$	5.2	$	242.2

Results by Quarter (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2018

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,
	2018			2017			2018			2017			2018			2017			2018			2017
Revenue:
Net revenue ^1,2	$	1,774.0		$	1,675.3		$	1,948.2		$	1,834.6		$	1,895.7		$	1,832.5		$	2,413.7		$	2,131.1
Billable expenses ^1,2	395.1			388.5			443.6			351.2			401.8			375.7			442.3			458.7
Total Revenue ^1,2	2,169.1			2,063.8			2,391.8			2,185.8			2,297.5			2,208.2			2,856.0			2,589.8

Operating Expenses:
Salaries and related expenses ²	1,330.3			1,251.7			1,292.9			1,228.9			1,251.4			1,218.8			1,423.7			1,291.3
Office and other direct ² expenses	323.8			312.7			333.3			318.4			317.0			302.9			381.0			334.8
Billable expenses ^1,2	395.1			388.5			443.6			351.2			401.8			375.7			442.3			458.7
Cost of services ²	2,049.2			1,952.9			2,069.8			1,898.5			1,970.2			1,897.4			2,247.0			2,084.8
Selling, general and administrative expenses ²	35.1			35.2			28.8			20.3			21.6			13.6			81.0			49.4
Depreciation and amortization ²	46.0			41.0			44.0			41.3			44.0			42.2			68.9			32.6
Total operating expenses ^1,2	2,130.3			2,029.1			2,142.6			1,960.1			2,035.8			1,953.2			2,396.9			2,166.8
Operating income ¹	38.8			34.7			249.2			225.7			261.7			255.0			459.1			423.0
Other (expense) income, net ³	(24.4		)	0.8			(16.3		)	(15.4		)	(15.3		)	(9.9		)	(13.6		)	(1.7		)
Total (expenses) and other income	(40.3		)	(14.9		)	(37.7		)	(36.4		)	(37.6		)	(26.8		)	(55.2		)	(19.5		)
Provision for (benefit of) income taxes^1,4	12.7			(0.3		)	63.6			81.6			60.7			54.9			62.2			135.1
Net (loss) income ¹	(16.1		)	21.3			147.8			107.6			163.5			172.3			342.5			269.2
Net (loss) income available to IPG common stockholders ¹	$	(14.1	)	$	24.7		$	145.8		$	107.7		$	161.0		$	169.7		$	326.2		$	252.3

(Loss) earnings per share available to IPG common stockholders:
Basic ¹	$	(0.04	)	$	0.06		$	0.38		$	0.27		$	0.42		$	0.44		$	0.85		$	0.66
Diluted ¹	$	(0.04	)	$	0.06		$	0.37		$	0.27		$	0.41		$	0.43		$	0.84		$	0.64

Dividends declared per common share	$	0.21		$	0.18		$	0.21		$	0.18		$	0.21		$	0.18		$	0.21		$	0.18


1	Effective January 1, 2018, the Company adopted Accounting Standards Codification Topic 606, Revenue from Contracts with Customers, ("ASC 606") using the full retrospective transition method and revised its Consolidated financial statements for the years ended December 31, 2017. See Note 1 and 2 for further detail on the ASC 606 adoption.


3	The three months ended March 31, June 30, September 30 and December 31, 2018 included pre-tax net losses of $24.4, $19.8, $5.8, and $11.9, respectively, on sales of businesses. 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.

Summary of Significant Accounting Policies (Details) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares
Revenue, remaining performance obligation, amount	$ 770.0
Retirement of treasury stock, amount	$ 0.0	$ 0.0	$ 0.0
ERP Systems, Useful Life	10
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	13
Foreign Currency Transaction pre-tax Gain (Loss)	$ 5.6	$ 1.9	$ 2.1
Minimum
Furniture and Equipment, Useful Life	3 years
Buildings, Useful Life	10 years
Other Internal Use Software, Useful Life	3
Identifiable 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
Identifiable Intangible Assets, Useful Life	15 years
Common Stock [Member]
Retirement of treasury stock, shares \| shares	(8.1)	(13.4)	(13.7)
Retirement of treasury stock, amount	$ (0.8)	$ (1.3)	$ (1.4)
Treasury Stock [Member]
Retirement of treasury stock, amount	176.1	304.4	311.0
Additional Paid-in Capital [Member]
Retirement of treasury stock, amount	$ (175.3)	$ (303.1)	$ (309.6)

Revenue Income Statement (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net revenue	$ 2,413.7	$ 1,895.7	$ 1,948.2	$ 1,774.0	$ 2,131.1	$ 1,832.5	$ 1,834.6	$ 1,675.3	$ 8,031.6	$ 7,473.5	$ 7,452.3
Billable expenses	442.3	401.8	443.6	395.1	458.7	375.7	351.2	388.5	1,682.8	1,574.1	1,603.9
Total revenue	2,856.0	2,297.5	2,391.8	2,169.1	2,589.8	2,208.2	2,185.8	2,063.8	9,714.4	9,047.6	9,056.2
OPERATING EXPENSES:
Salaries and related expenses	1,423.7	1,251.4	1,292.9	1,330.3	1,291.3	1,218.8	1,228.9	1,251.7	5,298.3	4,990.7	4,942.2
Office and other direct expenses	381.0	317.0	333.3	323.8	334.8	302.9	318.4	312.7	1,355.1	1,268.8	1,274.9
Billable expense	442.3	401.8	443.6	395.1	458.7	375.7	351.2	388.5	1,682.8	1,574.1	1,603.9
Cost of services	2,247.0	1,970.2	2,069.8	2,049.2	2,084.8	1,897.4	1,898.5	1,952.9	8,336.2	7,833.6	7,821.0
Selling, General and Administrative Expense	81.0	21.6	28.8	35.1	49.4	13.6	20.3	35.2	166.5	118.5	138.6
Depreciation and amortization	68.9	44.0	44.0	46.0	32.6	42.2	41.3	41.0	202.9	157.1	160.2
Total operating expenses	2,396.9	2,035.8	2,142.6	2,130.3	2,166.8	1,953.2	1,960.1	2,029.1	8,705.6	8,109.2	8,119.8
Operating Income (Loss)	459.1	261.7	249.2	38.8	423.0	255.0	225.7	34.7	1,008.8	938.4	936.4
EXPENSES AND OTHER INCOME:
Interest Expense									(123.0)	(90.8)	(90.6)
Interest income									21.8	19.4	20.1
Other expense, net	(13.6)	(15.3)	(16.3)	(24.4)	(1.7)	(9.9)	(15.4)	0.8	(69.6)	(26.2)	(40.3)
Total (expenses) and other income	(55.2)	(37.6)	(37.7)	(40.3)	(19.5)	(26.8)	(36.4)	(14.9)	(170.8)	(97.6)	(110.8)
Income before income taxes									838.0	840.8	825.6
Provision for income taxes	62.2	60.7	63.6	12.7	135.1	54.9	81.6	(0.3)	199.2	271.3	196.9
Income of consolidated companies									638.8	569.5	628.7
Equity in net (loss) income of unconsolidated affiliates									(1.1)	0.9	0.3
NET INCOME	$ 342.5	$ 163.5	$ 147.8	$ (16.1)	$ 269.2	$ 172.3	$ 107.6	$ 21.3	637.7	570.4	629.0
Net income attributable to noncontrolling interests									(18.8)	(16.0)	(24.0)
NET INCOME AVAILABLE TO IPG COMMON STOCKHOLDERS									$ 618.9	$ 554.4	$ 605.0
Earnings per share, Basic	$ 0.85	$ 0.42	$ 0.38	$ (0.04)	$ 0.66	$ 0.44	$ 0.27	$ 0.06	$ 1.61	$ 1.42	$ 1.52
Earnings per share, Diluted	$ 0.84	$ 0.41	$ 0.37	$ (0.04)	$ 0.64	$ 0.43	$ 0.27	$ 0.06	$ 1.59	$ 1.40	$ 1.48
Weighted-average number of common shares outstanding, Basic									383.3	389.6	397.9
Weighted-average number of common shares outstanding, Diluted									389.0	397.3	408.0
As Previously Reported [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net revenue										$ 7,508.7	$ 7,456.9
Billable expenses										373.7	389.7
Total revenue										7,882.4	7,846.6
OPERATING EXPENSES:
Salaries and related expenses										4,990.7	4,942.2
Office and other direct expenses										1,268.8	1,274.9
Billable expense										373.7	389.7
Cost of services										6,633.2	6,606.8
Selling, General and Administrative Expense										118.5	138.6
Depreciation and amortization										157.1	160.2
Total operating expenses										6,908.8	6,905.6
Operating Income (Loss)										973.6	941.0
EXPENSES AND OTHER INCOME:
Interest Expense										(90.8)	(90.6)
Interest income										19.4	20.1
Other expense, net										(26.2)	(40.3)
Total (expenses) and other income										(97.6)	(110.8)
Income before income taxes										876.0	830.2
Provision for income taxes										281.9	198.0
Income of consolidated companies										594.1	632.2
Equity in net (loss) income of unconsolidated affiliates										0.9	0.3
NET INCOME										595.0	632.5
Net income attributable to noncontrolling interests										(16.0)	(24.0)
NET INCOME AVAILABLE TO IPG COMMON STOCKHOLDERS										$ 579.0	$ 608.5
Earnings per share, Basic										$ 1.49	$ 1.53
Earnings per share, Diluted										$ 1.46	$ 1.49
Weighted-average number of common shares outstanding, Basic										389.6	397.9
Weighted-average number of common shares outstanding, Diluted										397.3	408.0
ASC 606 Adjustments [Member] \| Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net revenue										$ (35.2)	$ (4.6)
Billable expenses										1,200.4	1,214.2
Total revenue										1,165.2	1,209.6
OPERATING EXPENSES:
Salaries and related expenses										0.0	0.0
Office and other direct expenses										0.0	0.0
Billable expense										1,200.4	1,214.2
Cost of services										1,200.4	1,214.2
Selling, General and Administrative Expense										0.0	0.0
Depreciation and amortization										0.0	0.0
Total operating expenses										1,200.4	1,214.2
Operating Income (Loss)										(35.2)	(4.6)
EXPENSES AND OTHER INCOME:
Interest Expense										0.0	0.0
Interest income										0.0	0.0
Other expense, net										0.0	0.0
Total (expenses) and other income										0.0	0.0
Income before income taxes										(35.2)	(4.6)
Provision for income taxes										(10.6)	(1.1)
Income of consolidated companies										(24.6)	(3.5)
Equity in net (loss) income of unconsolidated affiliates										0.0	0.0
NET INCOME										(24.6)	(3.5)
Net income attributable to noncontrolling interests										0.0	0.0
NET INCOME AVAILABLE TO IPG COMMON STOCKHOLDERS										$ (24.6)	$ (3.5)
Earnings per share, Basic										$ (0.07)	$ (0.01)
Earnings per share, Diluted										$ (0.06)	$ (0.01)
Weighted-average number of common shares outstanding, Basic										0.0	0.0
Weighted-average number of common shares outstanding, Diluted										0.0	0.0

Revenue Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cash and cash equivalents	$ 673.4	$ 790.9
Accounts receivable, net of allowance	5,126.6	4,585.0
Expenditures billable to clients		0.0
Accounts receivable, billable to clients	1,900.6	1,747.4
Assets held for sale	5.7	5.7
Other current assets	476.6	346.5
Assets, Current	8,182.9	7,475.5
Deferred income taxes	247.0	234.0
Property, Plant and Equipment, Net	790.9	650.4
Goodwill	4,875.9	3,820.4	$ 3,674.4
Other intangible assets	1,094.7	140.7
Other non-current assets	428.9	383.7
Assets	15,620.3	12,704.7
Accounts Payable, Current	6,698.1	6,420.2
Accrued Liabilities, Current	806.9	674.7
Contract liabilities	533.9	484.7
Short-term borrowings	73.7	84.9
Current portion of long-term debt	0.1	2.0
Liabilities held for sale	11.2	8.8
Liabilities, Current	8,123.9	7,675.3
Long-term debt	3,660.2	1,285.6
Deferred compensation	422.7	476.6
Other non-current liabilities	812.8	768.8
Liabilities	13,019.6	10,206.3
Redeemable noncontrolling interests	167.9	252.1	252.8	$ 251.9
STOCKHOLDERS' EQUITY:
Common Stock, Value, Issued	38.3	38.6
Additional Paid in Capital	895.9	955.2
Retained Earnings (Accumulated Deficit)	2,400.1	2,104.5
Accumulated other comprehensive loss, net of tax	(941.1)	(827.8)	(964.4)
Stockholders' Equity before Treasury Stock	2,393.2	2,270.5
Treasury Stock, Value	0.0	59.0
Stockholders' Equity Attributable to Parent	2,393.2	2,211.5
Stockholders' Equity Attributable to Noncontrolling Interest	39.6	34.8
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	2,432.8	2,246.3	2,090.4	$ 2,001.8
Liabilities and Equity	$ 15,620.3	12,704.7
As Previously Reported [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cash and cash equivalents		790.9
Accounts receivable, net of allowance		4,585.0
Expenditures billable to clients		1,747.4
Accounts receivable, billable to clients		0.0
Assets held for sale		5.7
Other current assets		335.1
Assets, Current		7,464.1
Deferred income taxes		236.0
Property, Plant and Equipment, Net		650.4
Goodwill		3,820.4
Other non-current assets		383.6
Assets		12,695.2
Accounts Payable, Current		6,907.8
Accrued Liabilities, Current		674.7
Contract liabilities		0.0
Short-term borrowings		84.9
Current portion of long-term debt		2.0
Liabilities held for sale		8.8
Liabilities, Current		7,678.2
Long-term debt		1,285.6
Deferred compensation		476.6
Other non-current liabilities		766.9
Liabilities		10,207.3
Redeemable noncontrolling interests		252.1
STOCKHOLDERS' EQUITY:
Common Stock, Value, Issued		38.6
Additional Paid in Capital		955.2
Retained Earnings (Accumulated Deficit)		2,093.6
Accumulated other comprehensive loss, net of tax		(827.4)
Stockholders' Equity before Treasury Stock		2,260.0
Treasury Stock, Value		59.0
Stockholders' Equity Attributable to Parent		2,201.0
Stockholders' Equity Attributable to Noncontrolling Interest		34.8
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		2,235.8
Liabilities and Equity		12,695.2
ASC 606 Adjustments [Member] \| Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cash and cash equivalents		0.0
Accounts receivable, net of allowance		0.0
Expenditures billable to clients		(1,747.4)
Accounts receivable, billable to clients		1,747.4
Assets held for sale		0.0
Other current assets		11.4
Assets, Current		11.4
Deferred income taxes		(2.0)
Property, Plant and Equipment, Net		0.0
Goodwill		0.0
Other intangible assets		0.0
Other non-current assets		0.1
Assets		9.5
Accounts Payable, Current		(487.6)
Accrued Liabilities, Current		0.0
Contract liabilities		484.7
Short-term borrowings		0.0
Current portion of long-term debt		0.0
Liabilities held for sale		0.0
Liabilities, Current		(2.9)
Long-term debt		0.0
Deferred compensation		0.0
Other non-current liabilities		1.9
Liabilities		(1.0)
Redeemable noncontrolling interests		0.0
STOCKHOLDERS' EQUITY:
Common Stock, Value, Issued		0.0
Additional Paid in Capital		0.0
Retained Earnings (Accumulated Deficit)		10.9	35.6
Accumulated other comprehensive loss, net of tax		(0.4)	$ (1.9)
Stockholders' Equity before Treasury Stock		10.5
Treasury Stock, Value		0.0
Stockholders' Equity Attributable to Parent		10.5
Stockholders' Equity Attributable to Noncontrolling Interest		0.0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		10.5
Liabilities and Equity		$ 9.5

Revenue Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
NET INCOME	$ 342.5	$ 163.5	$ 147.8	$ (16.1)	$ 269.2	$ 172.3	$ 107.6	$ 21.3	$ 637.7	$ 570.4	$ 629.0
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization									202.9	157.1	160.2
Provision for uncollectible receivables									6.5	9.5	16.7
Amortization of restricted stock and other non-cash compensation									82.2	82.0	85.6
Net amortization of bond discounts and deferred financing costs									6.5	5.8	5.6
Deferred income tax provision									14.1	(9.5)	44.6
Net losses on sales of businesses									61.9	24.1	41.4
Other									1.2	12.7	35.5
Net Cash Provided by (Used in) Investing Activities [Abstract]
Accounts receivable									(603.8)	37.6	(220.7)
Expenditures billable to clients										0.0	0.0
Accounts receivable, billable to clients									(209.5)	(165.5)	(2.2)
Other current assets									(67.2)	50.1	0.5
Accounts payable									428.7	336.4	(147.4)
Accrued liabilities									(24.2)	(241.3)	(61.1)
Contract liabilities									44.9	(12.0)	20.6
Other non-current assets and liabilities									(16.8)	24.4	(95.5)
Net cash provided by operating activities									565.1	881.8	512.8
Net cash used in investing activities									(2,491.5)	(196.2)	(263.9)
Net cash provided by (used in) financing activities									1,853.2	(1,004.9)	(666.4)
Effect of foreign exchange rate changes on cash, cash equivalents and restricted cash									(47.3)	16.8	11.6
Net decrease in cash, cash equivalents and restricted cash									(120.5)	(302.5)	(405.9)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 677.2				797.7				$ 677.2	797.7	1,100.2	$ 1,506.1
As Previously Reported [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
NET INCOME										595.0	632.5
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization										157.1	160.2
Provision for uncollectible receivables										9.5	16.7
Amortization of restricted stock and other non-cash compensation										82.0	85.6
Net amortization of bond discounts and deferred financing costs										5.8	5.6
Deferred income tax provision										1.1	45.7
Net losses on sales of businesses										24.1	41.4
Other										12.7	35.5
Net Cash Provided by (Used in) Investing Activities [Abstract]
Accounts receivable										37.6	(220.7)
Expenditures billable to clients										(165.5)	(2.2)
Accounts receivable, billable to clients										0.0	0.0
Other current assets										27.4	(4.8)
Accounts payable										311.9	(126.1)
Accrued liabilities										(241.3)	(61.1)
Contract liabilities										0.0	0.0
Other non-current assets and liabilities										24.4	(95.5)
Net cash provided by operating activities										881.8	512.8
Net cash used in investing activities										(196.2)	(263.9)
Net cash provided by (used in) financing activities										(1,004.9)	(666.4)
Effect of foreign exchange rate changes on cash, cash equivalents and restricted cash										16.8	11.6
Net decrease in cash, cash equivalents and restricted cash										(302.5)	(405.9)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents					797.7					797.7	1,100.2	1,506.1
ASC 606 Adjustments [Member] \| Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
NET INCOME										(24.6)	(3.5)
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization										0.0	0.0
Provision for uncollectible receivables										0.0	0.0
Amortization of restricted stock and other non-cash compensation										0.0	0.0
Net amortization of bond discounts and deferred financing costs										0.0	0.0
Deferred income tax provision										(10.6)	(1.1)
Net losses on sales of businesses										0.0	0.0
Other										0.0	0.0
Net Cash Provided by (Used in) Investing Activities [Abstract]
Accounts receivable										0.0	0.0
Expenditures billable to clients										165.5	2.2
Accounts receivable, billable to clients										(165.5)	(2.2)
Other current assets										22.7	5.3
Accounts payable										24.5	(21.3)
Accrued liabilities										0.0	0.0
Contract liabilities										(12.0)	20.6
Other non-current assets and liabilities										0.0	0.0
Net cash provided by operating activities										0.0	0.0
Net cash used in investing activities										0.0	0.0
Net cash provided by (used in) financing activities										0.0	0.0
Effect of foreign exchange rate changes on cash, cash equivalents and restricted cash										0.0	0.0
Net decrease in cash, cash equivalents and restricted cash										0.0	0.0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents					$ 0.0					$ 0.0	$ 0.0	$ 0.0

Revenue Major Geographical Area (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Total revenue	$ 2,856.0	$ 2,297.5	$ 2,391.8	$ 2,169.1	$ 2,589.8	$ 2,208.2	$ 2,185.8	$ 2,063.8	$ 9,714.4	$ 9,047.6	$ 9,056.2
Net revenue	$ 2,413.7	$ 1,895.7	$ 1,948.2	$ 1,774.0	$ 2,131.1	$ 1,832.5	$ 1,834.6	$ 1,675.3	8,031.6	7,473.5	7,452.3
United States
Total revenue									5,851.0	5,417.3	5,452.6
Net revenue									4,825.0	4,458.8	4,443.2
Total International
Total revenue									3,863.4	3,630.3	3,603.6
Net revenue									3,206.6	3,014.7	3,009.1
United Kingdom
Total revenue									881.4	775.7	788.8
Net revenue									711.7	613.1	604.3
Continental Europe
Total revenue									840.2	780.6	764.1
Net revenue									737.5	687.8	682.0
Asia Pacific
Total revenue									1,170.8	1,106.4	1,076.0
Net revenue									896.8	866.9	887.7
Latin America
Total revenue									389.0	386.6	417.2
Net revenue									350.1	350.8	367.8
Other
Total revenue									582.0	581.0	557.5
Net revenue									510.5	496.1	467.3
CMG
Total revenue									2,158.3	2,038.0	2,063.4
Net revenue									1,264.1	1,206.8	1,250.9
CMG \| United States
Total revenue									1,404.0	1,355.0	1,376.7
Net revenue									824.6	798.2	842.9
CMG \| Total International
Total revenue									754.3	683.0	686.7
Net revenue									439.5	408.6	408.0
IAN
Total revenue									7,374.4	7,009.6	6,992.8
Net revenue									6,585.8	6,266.7	6,201.4
IAN \| United States
Total revenue									4,279.4	4,062.3	4,075.9
Net revenue									3,832.7	3,660.6	3,600.3
IAN \| Total International
Total revenue									3,095.0	2,947.3	2,916.9
Net revenue									$ 2,753.1	$ 2,606.1	$ 2,601.1

Revenue Contract Balances (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Accounts receivable, net of allowance of $42.5 and $42.7, respectively	$ 5,126.6	$ 4,585.0
Accounts receivable, billable to clients	1,900.6	1,747.4
Contract with Customer, Asset, Net	67.9	11.5
Contract liabilities	$ 533.9	$ 484.7

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

12 Months Ended

Dec. 31, 2018

Dec. 31, 2017

Long-term debt, current maturities

$ 3,660.3

$ 1,287.6

0.1

2.0

Long-term debt, excluding current maturities

3,660.2

1,285.6

26.0

13.0

3.50% Notes Due 2020 (less unamortized discount and issuance costs of $0.9 and $2.9, respectively)

3,643.6

500.0

496.6

0.0

0.8

2.6

$ 499.9

0.0

Oct. 01, 2020

Debt instrument, interest rate, effective percentage

3.50%

3.89%

3.75% Notes Due 2021 (less unamortized discount and issuance costs of $0.3 and $3.2, respectively)

$ 500.0

496.8

0.0

0.3

2.9

$ 503.2

0.0

Oct. 01, 2021

Debt instrument, interest rate, effective percentage

3.75%

3.98%

4.00% Notes Due 2022 (less unamortized discount and issuance costs of $1.1 and $0.9, respectively)

$ 250.0

248.2

247.6

1.0

0.8

^[1]

$ 250.3

259.0

Mar. 15, 2022

Debt instrument, interest rate, effective percentage

4.00%

4.13%

3.75% Notes Due 2023 (less unamortized discount and issuance costs of $0.7 and $1.8, respectively)

$ 500.0

497.7

497.1

0.6

1.7

^[1]

$ 491.4

513.2

Feb. 15, 2023

Debt instrument, interest rate, effective percentage

3.75%

4.32%

4.20% Notes Due 2024 (less unamortized discount and issuance costs of $0.6 and $2.3, respectively)

$ 500.0

497.3

496.7

0.5

2.2

^[1]

$ 492.6

524.2

Apr. 15, 2024

Debt instrument, interest rate, effective percentage

4.20%

4.24%

4.65% Notes Due 2028 (less unamortized discount and issuance costs of $1.7 and $4.4, respectively)

$ 500.0

494.0

0.0

1.7

4.3

$ 494.1

0.0

Oct. 01, 2028

Debt instrument, interest rate, effective percentage

4.65%

4.78%

5.40% Notes Due 2048 (less unamortized discount and issuance costs of $2.8 and $5.6, respectively)

$ 500.0

491.7

0.0

2.8

5.5

$ 474.1

0.0

Oct. 01, 2048

Debt instrument, interest rate, effective percentage

5.40%

5.48%

Term Loan Due 2021 (LIBOR plus 1.25%)

Loans Payable, Fair Value Disclosure

$ 400.0

400.0

Other notes payable and capitalized leases

38.0

46.2

Line of Credit Facility [Line Items]

^[1]

$ 38.0

$ 46.2

[1]	See Note 12 for information on the fair value measurement of our long-term debt.

Debt and Credit Agreements Debt Transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 21, 2018
Schedule of New Debt Issuance [Line Items]
Debt Instrument, Redemption Price, Percentage	101.00%
Debt Instrument Change of Control Repurchase Event Price Percentage	101.00%
Term Loan		$ 500.0
3.50% Notes Due 2020
Schedule of New Debt Issuance [Line Items]
Debt Instrument, Face Amount	$ 500.0
Debt Issuance Face Amount			$ 500.0
Unamortized Discount at Issuance			1.0
Senior Notes Net of Discount			499.0
Debt Issuance Cost at Issuance			2.9
Senior Notes			496.1
3.75% Notes Due 2021
Schedule of New Debt Issuance [Line Items]
Debt Instrument, Face Amount	500.0
Debt Issuance Face Amount			500.0
Unamortized Discount at Issuance			0.3
Senior Notes Net of Discount			499.7
Debt Issuance Cost at Issuance			3.2
Senior Notes			496.5
4.65% Notes Due 2028
Schedule of New Debt Issuance [Line Items]
Debt Instrument, Face Amount	500.0
Debt Issuance Face Amount			500.0
Unamortized Discount at Issuance			1.7
Senior Notes Net of Discount			498.3
Debt Issuance Cost at Issuance			4.4
Senior Notes			493.9
5.40% Notes Due 2048
Schedule of New Debt Issuance [Line Items]
Debt Instrument, Face Amount	$ 500.0
Debt Issuance Face Amount			500.0
Unamortized Discount at Issuance			2.8
Senior Notes Net of Discount			497.2
Debt Issuance Cost at Issuance			5.6
Senior Notes			491.6
Aggregate Senior Notes Issued [Domain]
Schedule of New Debt Issuance [Line Items]
Debt Issuance Face Amount			2,000.0
Unamortized Discount at Issuance			5.8
Senior Notes Net of Discount			1,994.2
Debt Issuance Cost at Issuance			16.1
Senior Notes			$ 1,978.1

Debt and Credit Agreements Annual Maturities (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Debt Disclosure [Abstract]
Long-term debt, maturities, repayments of principal in next twelve months	$ 0.1
Long-term debt, maturities, repayments of principal in year two	496.9
Long-term debt, maturities,repayments of principal in year three	896.8
Long-term debt, maturities, repayments of principal in year four	248.2
Long-term debt, maturities, repayments of principal in year five	497.7
Long-term debt, maturities, repayments of principal after year five	1,520.6
Total long-term debt	$ 3,660.3	$ 1,287.6

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

3 Months Ended

12 Months Ended

Sep. 30, 2018

Dec. 31, 2018

Dec. 31, 2017

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]

4.00x

Quarters 1-3 Maximum Leverage Ratio Covenant

4.00 to 1.00

Quarters 4-7 Maximum Leverage Ratio Covenant

3.75 to 1.00

Quarters 8-Thereafter Maximum Leverage Ratio Covenant

3.50 to 1.00

Committed credit facility [Member]

Line of Credit Facility [Line Items]

Line of credit facility, maximum borrowing capacity

$ 1,500.0

Line of credit facility, available capacity increase amount

250.0

Limits on letters of credit

50.0

Line of credit facility, amount outstanding

0.0

Letters of credit, amount outstanding

8.5

$ 8.4

Line of credit facility, remaining borrowing capacity

1,491.5

1,491.6

Uncommitted credit facility

Line of Credit Facility [Line Items]

Line of credit facility, amount outstanding

73.7

84.9

Line of credit facility, current borrowing capacity

1,173.1

926.2

Line of credit facility, average outstanding amount

$ 96.4

$ 223.8

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

4.50%

2.90%

[1]	The interest coverage ratio is defined as EBITDA, as defined in the Credit Agreement and Term Loan Agreement, to net interest expense for the four quarters then ended.
[2]	The leverage ratio is defined as debt as of the last day of such fiscal quarter to EBITDA, as defined in the Amended Credit Agreement and Term Loan Agreement, for the four quarters then ended.

Debt and Credit Agreements Commercial Paper (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Debt Disclosure [Abstract]
Commercial paper, current borrowing capacity	$ 1,500.0
Commercial paper, amount outstanding	0.0
Commercial paper, average outstanding amount	$ 648.7
Commercial paper, weighted average interest rate, over time	2.40%
Commercial paper, weighted-average maturity days outstanding, over time	22

Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
NET INCOME AVAILABLE TO IPG COMMON STOCKHOLDERS									$ 618.9	$ 554.4	$ 605.0
Weighted-average number of common shares outstanding, Basic									383.3	389.6	397.9
Restricted stock, stock options and other equity awards									5.7	7.7	10.1
Weighted-average number of common shares outstanding, Diluted									389.0	397.3	408.0
Basic	$ 0.85	$ 0.42	$ 0.38	$ (0.04)	$ 0.66	$ 0.44	$ 0.27	$ 0.06	$ 1.61	$ 1.42	$ 1.52
Diluted	$ 0.84	$ 0.41	$ 0.37	$ (0.04)	$ 0.64	$ 0.43	$ 0.27	$ 0.06	$ 1.59	$ 1.40	$ 1.48

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

+ References

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-Name Accounting Standards Codification
-Topic 944
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+ Details

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
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+ Details

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

Acquisitions Cash Paid for Acquisitions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Paid for Acquisitions [Abstract]
Cost of investment: current-year acquisitions 1	$ 2,323.4	$ 36.8	$ 65.7
Cost of investment: prior-year acquisitions	33.9	54.6	40.7
Less: net cash acquired	(13.8)	(7.1)	(13.6)
Total cost of investment	2,343.5	84.3	92.8
Operating payments	19.4	47.1	19.1
Total cash paid for acquisitions	2,362.9	131.4	111.9
Acquisitions, net of cash acquired	2,309.8	30.6	52.0
Payments for previous acquisition, financing cash flows	$ 33.7	$ 53.7	$ 40.8

Redeemable Noncontrolling Interests (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Redeemable Noncontrolling Interests
Balance at beginning of period	$ 252.1	$ 252.8	$ 251.9
Change in related noncontrolling interest balance	(10.7)	(2.8)	4.9
Changes in redemption value of redeemable noncontrolling interests:
Additions	0.0	7.7	6.8
Redemptions and other	(33.7)	(18.5)	(14.8)
Redemption value adjustments	(39.8)	12.9	4.0
Balance at end of period	$ 167.9	$ 252.1	$ 252.8

Acxiom Acquisition Preliminary fair values of the assets acquired and liabilities assumed (Details) - Acxiom - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Oct. 01, 2018
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents		$ 13.3
Accounts receivable, net of allowance		112.9
Accounts receivable, billable to clients		8.3
Other current assets		28.2
Property, Plant and Equipment, Other, Net		159.7
Deferred Income Taxes and Other Tax Liabilities, Noncurrent		(0.6)
Goodwill		1,110.8
Intangible Assets, Net (excluding Goodwill)		995.0
Other non-current assets		8.3
Accounts Payable		(37.1)
Accrued Liabilities		(46.9)
Contract liabilities		23.2
Other non-current liabilities		0.8
Net Asset Acquired		2,327.9
Identifiable Intangible Assets		995.0
Customer Lists with useful life of 15 years
Identifiable Intangible Assets, Useful Life	15 years
Identifiable Intangible Assets		600.0
Know-how technology with useful life with 9 years
Identifiable Intangible Assets, Useful Life	9 years
Identifiable Intangible Assets		235.0
Trade Names with useful life 15 years to indefinite
Identifiable Intangible Assets		$ 160.0

Acxiom Acquisition Operating Results (Three Months in 2018) (Details) - Acxiom $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Net revenue	$ 181.7
NET INCOME AVAILABLE TO IPG COMMON STOCKHOLDERS	$ 20.4

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

Supplemental Cash Flow Information [Abstract]

Acxiom Acquisition Transaction Related (Details) - Acxiom $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Term Loan	$ 500.0
Debt Issuance Face Amount	2,000.0
Selling, General and Administrative Expense	35.0
Interest Expense	3.7
Interest Income	0.4
Other expense, net	$ 10.3

Acxiom Acquisition Pro Forma (Details) - Acxiom - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition, Pro Forma Revenue	$ 10,230.4	$ 9,736.1
Business Acquisition, Pro Forma Net Income (Loss)	$ 642.2	$ 519.2
After-tax nonrecurring transaction-related charges		27.6

Valuation and Qualifying Accounts - Allowance for Uncollectible Accounts Receivable (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 42.7	$ 55.7	$ 54.2
Charges to costs and expenses	6.5	9.5	16.7
Adjustments:
Acquisitions/(dispositions)	2.2	(1.0)	(2.5)
Uncollectible accounts written off	(7.1)	(25.5)	(9.4)
Foreign currency translation adjustment	(1.8)	4.0	(3.3)
Balance at end of period	$ 42.5	$ 42.7	$ 55.7

Supplementary Data Property and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property and Equipment [Abstract]
Depreciation	$ 165.3	$ 136.0	$ 138.3
Property, Plant and Equipment [Line Items]
Furniture and equipment	681.7	634.8
Leasehold improvements	629.0	641.5
Internal-use computer software	368.5	331.3
Land and buildings	146.6	79.0
Total property and equipment, gross	1,825.8	1,686.6
Less: accumulated depreciation	(1,034.9)	(1,036.2)
Total property and equipment, net	$ 790.9	$ 650.4

Accrued Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Accrued Liabilities [Abstract]
Salaries, benefits and related expenses	$ 494.9	$ 441.7
Office and related expenses	52.2	53.2
Acquisition obligations	65.7	42.0
Interest	43.6	16.4
Other	150.5	121.4
Total accrued liabilities	$ 806.9	$ 674.7

Other Expense, Net (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
Other Expense, Net (Details) - USD ($) $ in Millions	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Nonoperating Income (Expense) [Abstract]
Net losses on sales of businesses									$ (61.9)	$ (24.1)	$ (41.4)
Other									(7.7)	(2.1)	1.1
Total other expense, net	$ (13.6)	$ (15.3)	$ (16.3)	$ (24.4)	$ (1.7)	$ (9.9)	$ (15.4)	$ 0.8	$ (69.6)	$ (26.2)	$ (40.3)

Share Repurchase Program (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of shares repurchased	5.1	13.7	13.3
Aggregate cost, including fees	$ 117.1	$ 300.1	$ 303.3
Average price per share, including fees	$ 23.03	$ 21.97	$ 22.76
2017 Share Repurchase Program
Share repurchase program, initial authorized amount	$ 300.0
Stock repurchase program, remaining authorized repurchase amount	$ 338.4

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

12 Months Ended

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2016

Cash paid for interest

$ 88.7

$ 82.3

$ 78.8

Cash paid for income taxes, net of refunds

^[1]

207.9

228.4

244.1

Tax refunds

$ 24.3

$ 31.9

$ 26.6

[1]	Refunds of $24.3, $31.9 and $26.6 were received for the years ended December 31, 2018, 2017 and 2016, respectively.

Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
Goodwill (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill
Goodwill	$ 4,875.9	$ 3,820.4	$ 3,674.4
Current year acquisitions	1,132.0	55.1
Foreign currency and other	(76.5)	90.9
IAN
Goodwill
Goodwill	3,099.7	3,161.8	3,043.8
Current year acquisitions	1.2	39.6
Foreign currency and other	(63.3)	78.4
CMG
Goodwill
Goodwill	666.6	658.6	630.6
Current year acquisitions	20.0	15.5
Foreign currency and other	(12.0)	12.5
Corporate and Other
Goodwill
Goodwill	1,109.6	0.0	$ 0.0
Current year acquisitions	1,110.8	0.0
Foreign currency and other	$ (1.2)	$ 0.0

Other Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
Other Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Future amortization expense 2018	$ 87.8
Future amortization expense 2019	87.3
Future amortization expense 2020	85.6
Future amortization expense 2021	82.3
Future amortization expense 2022	78.2
Finite-Lived Intangible Assets [Line Items]
Amortization expense of intangible assets	37.6	$ 21.1	$ 21.9
Acquired finite-lived intangible assets related to acquisitions	999.0	7.0
Gross Amount	1,332.8	350.5
Accumulated Amortization	(238.0)	(209.8)
Net Amount	1,094.8	140.7
Customer lists
Finite-Lived Intangible Assets [Line Items]
Gross Amount	857.2	267.3
Accumulated Amortization	(190.9)	(172.2)
Net Amount	666.3	95.1
know-how technology
Finite-Lived Intangible Assets [Line Items]
Gross Amount	235.0	0.0
Accumulated Amortization	(6.5)	0.0
Net Amount	228.5	0.0
Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Amount	226.2	68.8
Accumulated Amortization	(36.8)	(33.8)
Net Amount	189.4	35.0
Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross Amount	14.4	14.4
Accumulated Amortization	(3.8)	(3.8)
Net Amount	$ 10.6	$ 10.6
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

Components of Income Before Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income before income taxes, Domestic	$ 474.0	$ 514.8	$ 502.1
Income before income taxes, Foreign	364.0	326.0	323.5
Income before income taxes	$ 838.0	$ 840.8	$ 825.6

Provision for Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
U.S. federal income taxes (including foreign withholding taxes):
Current federal income taxes									$ 38.1	$ 154.1	$ 54.3
Deferred federal income taxes									29.9	(37.6)	35.7
Total federal income taxes									68.0	116.5	90.0
State and local income taxes:
Current state and local income taxes									25.1	18.8	8.2
Deferred state and local income taxes									3.4	19.7	(1.6)
Total state and local income taxes									28.5	38.5	6.6
Foreign income taxes:
Current foreign income taxes									121.9	107.9	89.8
Deferred foreign income taxes									(19.2)	8.4	10.5
Total foreign income taxes									102.7	116.3	100.3
Provision for income taxes	$ 62.2	$ 60.7	$ 63.6	$ 12.7	$ 135.1	$ 54.9	$ 81.6	$ (0.3)	$ 199.2	$ 271.3	$ 196.9

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

3 Months Ended

12 Months Ended

Dec. 31, 2018

Sep. 30, 2018

Jun. 30, 2018

Mar. 31, 2018

Dec. 31, 2017

Sep. 30, 2017

Jun. 30, 2017

Mar. 31, 2017

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2016

Effective Income Tax Rate Reconciliation, Percent [Abstract]

U.S. federal statutory income tax rate

21.00%

35.00%

Income tax provision at U.S. federal statutory rate

$ 176.0

$ 294.3

$ 289.0

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

23.8

23.5

4.3

Impact of foreign operations, including withholding taxes

50.7

(6.7)

(23.9)

U.S. tax incentives

(17.5)

(1.3)

Change in net valuation allowance

^[1]

(16.9)

1.4

(13.4)

Divestitures

11.7

1.1

9.7

U.S. federal tax credits

(48.1)

(0.4)

(44.6)

Stock compensation

(6.8)

(15.3)

(9.0)

Change in unrecognized tax benefits

8.4

7.0

(21.8)

Net impact of the Tax Act

13.4

(36.0)

0.0

Statutory tax rate changes

0.0

11.4

Other

4.5

3.7

(3.5)

Provision for income taxes

$ 62.2

$ 60.7

$ 63.6

$ 12.7

$ 135.1

$ 54.9

$ 81.6

$ (0.3)

$ 199.2

$ 271.3

$ 196.9

Effective income tax rate on operations

23.80%

32.30%

23.80%

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

Components of Deferred Tax Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Tax Assets, Net [Abstract]
Postretirement/post-employment benefits	$ 17.9	$ 19.5
Deferred compensation	99.8	91.7
Pension costs	22.2	27.6
Basis differences in fixed assets	(71.7)	(52.0)
Rent	27.3	27.5
Interest	48.8	45.8
Accruals and reserves	21.0	18.4
Allowance for doubtful accounts	7.4	10.2
Basis differences in intangible assets	(302.7)	(281.3)
Investments in equity securities	1.2	(3.3)
Tax loss/tax credit carry forwards	345.6	357.9
Prepaid expenses	(6.3)	(1.7)
Deferred revenue	(26.8)	(41.3)
Unremitted foreign earnings	(9.5)	0.0
Other	38.2	43.7
Total deferred tax assets, net	212.4	262.7
Valuation allowance	(211.0)	(243.0)	$ (255.6)	$ (275.1)
Net deferred tax assets	$ 1.4	$ 19.7

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

12 Months Ended

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2016

Summary of Valuation Allowances

Beginning balance

$ 243.0

$ 255.6

$ 275.1

Reversed to costs and expenses

(28.0)

(4.6)

(15.4)

Charged (reversed) to gross tax assets and other accounts 1

^[1]

5.1

(27.3)

9.5

Foreign currency translation

(9.1)

19.3

(13.6)

Ending balance

211.0

$ 243.0

$ 255.6

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

Operating Loss Carryforwards

1,149.4

Undistributed Earnings of Foreign Subsidiaries

1,079.1

Foreign Tax Authority

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

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

994.1

Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration

155.3

State and Local Jurisdiction

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

Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration

$ 26.8

Minimum | Foreign Tax Authority

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

Minimum | State and Local Jurisdiction

Jan. 01, 2019

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

Maximum | Foreign Tax Authority

Jan. 01, 2019

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

Maximum | State and Local Jurisdiction

Jan. 01, 2038

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

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

Jan. 01, 2038

[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, 2018	Dec. 31, 2017	Dec. 31, 2016
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued [Abstract]
Balance at beginning of period	$ 271.9	$ 246.7	$ 226.9
Increases as a result of tax positions taken during a prior year	65.9	6.3	65.0
Decreases as a result of tax positions taken during a prior year	(10.8)	(8.1)	(47.5)
Settlements with taxing authorities	(6.5)	(0.8)	(4.6)
Lapse of statutes of limitation	(1.7)	(3.3)	(11.8)
Increases as a result of tax positions taken during the current year	16.6	31.1	18.7
Balance at end of period	335.4	271.9	$ 246.7
Income Tax Contingency [Line Items]
Unrecognized tax benefits that would impact effective tax rate	313.5
Income tax penalties and interest accrued	42.4	27.9
Income tax penalties and interest expense	14.5	$ 7.0
Minimum [Member]
Income Tax Contingency [Line Items]
Anticipated decrease in unrecognized tax benefits	15.0
Maximum [Member]
Income Tax Contingency [Line Items]
Anticipated decrease in unrecognized tax benefits	$ 25.0
Foreign Tax Authority \| Minimum [Member]
Income Tax Contingency [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 01, 2019
Foreign Tax Authority \| Maximum [Member]
Income Tax Contingency [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 01, 2038

Accumulated Other Comprehensive Loss, Net of Tax Changes in AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Available-for-sale securities, before reclassifications	$ 0.0	$ 0.0	$ 0.5
Total other comprehensive income, before reclassifications	(135.4)	122.5
Total reclassification from AOCI	22.1	14.1	8.1
Accumulated other comprehensive loss, net of tax	(941.1)	(827.8)	(964.4)
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Foreign currency translation adjustment, before reclassifications	(146.8)	132.2
Foreign currency translation adjustment, amount reclassified from AOCI, net of tax	15.7	1.1
Foreign currency translation adjustment, net of tax	(716.4)	(585.3)	(718.6)
Available-for-sale Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Available-for-sale securities, before reclassifications	0.0	0.0
Available-for-sale securities, amount reclassified from AOCI, net of tax	0.0	(0.6)
Available-for-sale securities adjustment, net of tax	0.0	0.0	0.6
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	1.5	1.6
Derivative Instruments, net of tax	(5.3)	(6.8)	(8.4)
Defined Benefit and Postretirement Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined Benefit and Postretirement Plans, before reclassifications	11.4	(9.7)
Defined benefit and Postretirement Plans, amount reclassified from AOCI, net of tax	4.9	12.0
Pension and Other Postretirement Benefit Plans, net of tax	$ (219.4)	$ (235.7)	$ (238.0)

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

12 Months Ended

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2016

Total income tax effect

$ (2.3)

$ (2.1)

Total reclassified from AOCI, net of tax

22.1

14.1

8.1

Foreign Currency Translation Adjustment

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

Available-for-sale Securities

^[1]

15.7

1.1

3.7

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

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

0.0

(0.7)

(1.3)

Derivative Instruments

Defined Benefit and Postretirement Plans

2.2

2.1

2.0

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

$ 6.5

$ 13.7

$ 5.8

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

Plan Information (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Deferred Compensation Liability, Current and Noncurrent	$ 196.2	$ 213.2
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, 2018

Dec. 31, 2017

Dec. 31, 2016

$ 84.6

$ 84.5

$ 88.0

Tax benefit

20.4

30.4

32.1

Employee Stock Option

0.0

0.2

Stock-settled awards

24.7

20.5

16.0

Cash-settled awards

0.6

1.0

0.9

Performance-based awards

Employee stock purchase plan

57.5

61.5

69.4

0.9

1.0

0.7

Other

Fair value assets and liabilities measured on recurring basis

^[1]

$ 0.9

$ 0.5

$ 0.8

[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, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock-based Payment Award
Intrinsic value of stock options exercised	$ 27.9	$ 15.1	$ 15.2
Proceeds from stock options exercised including taxes withheld	29.0	20.0	18.2
Tax withheld on stock options received	$ 13.3	$ 6.8	$ 7.8
Employee Stock Option
Stock-based Payment Award
Stock options outstanding as of January 1, 2018	3.7
Stock options outstanding as of Jan 1, 2018, Weighted-average exercise price	$ 9.44
Exercised	(1.9)	(1.1)	(1.2)
Exercised, weighted-average exercise price	$ 8.30
Stock options outstanding as of December 31, 2018	1.8	3.7
Stock options outstanding as of Dec 31, 2018, Weighted-average exercise price	$ 10.66	$ 9.44
Options outstanding, weighted average remaining contractual term	2 years 9 months
Stock options outstanding, aggregate intrinsic value	$ 17.6

Share-based Compensation Awards (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock-settled awards
Stock-based Payment Award
Awards granted	2.1	0.8	1.1
Weighted-average grant-date fair value (per award)	$ 23.60	$ 24.18	$ 21.87
Total fair value of vested awards distributed	$ 24.2	$ 22.6	$ 17.5
Accrued dividends on non-vested stock-settled awards	2.4	1.5
Dividends paid for stock-settled awards	$ 1.5	$ 1.2
Cash-settled awards
Stock-based Payment Award
Awards granted	0.1	0.0	0.1
Weighted-average grant-date fair value (per award)	$ 23.62	$ 23.33	$ 22.54
Total fair value of vested awards distributed	$ 0.8	$ 0.9	$ 0.7
Performance-based awards
Stock-based Payment Award
Awards granted	2.9	4.8	3.3
Weighted-average grant-date fair value (per award)	$ 21.13	$ 20.06	$ 19.58
Total fair value of vested awards distributed	$ 87.2	$ 112.4	$ 27.9

Non-vested Award Activity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock-settled awards
Stock-based Payment Award
Non-vested as of January 1, 2018	2.1
Nonvested as of January 1, 2018, weighted-average grant date fair value	$ 22.78
Granted	2.1
Granted, Weighted-average grant-date fair value	$ 23.60	$ 24.18	$ 21.87
Vested	(1.0)
Vested, Weighted-average grant date fair value	$ 22.18
Forfeited	(0.1)
Forfeited, Weighted-average grant date fair value	$ 23.67
Non-vested as of December 31, 2018	3.1	2.1
Nonvested as of December 31, 2018, weighted-average grant date fair value	$ 23.51	$ 22.78
Total unrecognized compensation expense remaining	$ 39.4
Weighted-average years expected to be recognized over	1 year 7 months
Cash-settled awards
Stock-based Payment Award
Non-vested as of January 1, 2018	0.1
Nonvested as of January 1, 2018, weighted-average grant date fair value	$ 22.52
Granted	0.1
Granted, Weighted-average grant-date fair value	$ 23.62	$ 23.33	$ 22.54
Vested	(0.1)
Vested, Weighted-average grant date fair value	$ 21.54
Forfeited	0.0
Forfeited, Weighted-average grant date fair value	$ 23.17
Non-vested as of December 31, 2018	0.1	0.1
Nonvested as of December 31, 2018, weighted-average grant date fair value	$ 23.47	$ 22.52
Total unrecognized compensation expense remaining	$ 1.0
Weighted-average years expected to be recognized over	1 year 3 months
Cash awards granted during the period target value	$ 20.9	$ 2.8	$ 5.2
Incentive compensation expense, non share-based	$ 7.0	$ 2.5	$ 3.1
Performance-based awards
Stock-based Payment Award
Non-vested as of January 1, 2018	8.3
Nonvested as of January 1, 2018, weighted-average grant date fair value	$ 21.05
Granted	2.9
Granted, Weighted-average grant-date fair value	$ 21.13	$ 20.06	$ 19.58
Vested	(3.6)
Vested, Weighted-average grant date fair value	$ 21.02
Forfeited	(0.6)
Forfeited, Weighted-average grant date fair value	$ 21.06
Non-vested as of December 31, 2018	7.0	8.3
Nonvested as of December 31, 2018, weighted-average grant date fair value	$ 21.10	$ 21.05
Total unrecognized compensation expense remaining	$ 54.7
Weighted-average years expected to be recognized over	1 year 8 months
Cash awards granted during the period target value	$ 39.9	$ 38.4	$ 37.4
Incentive compensation expense, non share-based	$ 37.6	$ 35.3	$ 39.8

Incentive Compensation Plans Employee Stock Purchase Plans (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2016
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	800,000	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, 2018

Dec. 31, 2017

$ 132.1

$ 201.6

Contingent acquisition obligation, total change

^[1]

148.4

147.0

1.4

Contingent acquisition obligation, payments

(54.0)

Contingent acquisition obligation, additions

61.8

Level 1

Fair value assets and liabilities measured on recurring basis

132.1

201.6

Fair value assets and liabilities measured on recurring basis

^[1]

0.0

Level 2

0.0

Fair value assets and liabilities measured on recurring basis

^[1]

0.0

Level 3

0.0