Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Additional Paid-In Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Loss, Net of Tax	Treasury Stock	Total IPG Stockholders' Equity	Noncontrolling Interests
Balance at Dec. 31, 2015	$ 2,001.8	$ 40.4	$ 1,404.1	$ 1,437.6	$ (845.6)	$ (71.0)	$ 1,965.5	$ 36.3
Balance, shares at Dec. 31, 2015		404.4
Cumulative effect of accounting change	39.1			39.1			39.1
NET INCOME	629.0			605.0			605.0	24.0
Other comprehensive income	(119.9)				(118.8)		(118.8)	(1.1)
Reclassifications related to redeemable noncontrolling interests	(5.8)							(5.8)
Distributions to noncontrolling interests	(13.7)							(13.7)
Change in redemption value of RNCI	(2.1)			(2.1)			(2.1)
Repurchases of common stock	(303.3)					(303.3)	(303.3)
Retirement of treasury stock, shares		(13.7)
Retirement of treasury stock	0.0	$ (1.4)	(309.6)			311.0	0.0
Common stock dividends	(238.4)			(238.4)			(238.4)
Stock-based compensation, shares		3.5
Stock-based compensation, Value	117.1	$ 0.4	116.7				117.1
Exercise of stock options, shares		1.2
Exercise of stock options, Value	10.3	$ 0.1	10.2				10.3
Shares withheld for taxes, shares		(1.1)
Shares withheld for taxes, value	(23.3)	$ (0.1)	(23.2)				(23.3)
Other	(0.4)		1.0	(1.3)			(0.3)	(0.1)
Balance, shares at Dec. 31, 2016		394.3
Balance at Dec. 31, 2016	2,090.4	$ 39.4	1,199.2	1,839.9	(964.4)	(63.3)	2,050.8	39.6
NET INCOME	570.4			554.4			554.4	16.0
Other comprehensive income	138.1				136.6		136.6	1.5
Reclassifications related to redeemable noncontrolling interests	0.6		(0.3)				(0.3)	0.9
Distributions to noncontrolling interests	(20.9)							(20.9)
Change in redemption value of RNCI	(7.9)			(7.9)			(7.9)
Repurchases of common stock	(300.1)					(300.1)	(300.1)
Retirement of treasury stock, shares		(13.4)
Retirement of treasury stock	0.0	$ (1.3)	(303.1)			304.4	0.0
Common stock dividends	(280.3)			(280.3)			(280.3)
Stock-based compensation, shares		5.7
Stock-based compensation, Value	87.0	$ 0.6	86.4				87.0
Exercise of stock options, shares		1.2
Exercise of stock options, Value	13.2	$ 0.1	13.1				13.2
Shares withheld for taxes, shares		(1.6)
Shares withheld for taxes, value	(39.0)	$ (0.2)	(38.8)				(39.0)
Other	(5.2)		1.3	(1.6)			(2.9)	(2.3)
Balance, shares at Dec. 31, 2017		386.2
Balance at Dec. 31, 2017	2,246.3	$ 38.6	955.2	2,104.5	(827.8)	(59.0)	2,211.5	34.8
NET INCOME	637.7			618.9			618.9	18.8
Other comprehensive income	(116.1)				(113.3)		(113.3)	(2.8)
Reclassifications related to redeemable noncontrolling interests	2.4							2.4
Distributions to noncontrolling interests	(16.9)							(16.9)
Change in redemption value of RNCI	42.9		41.8	1.1			42.9
Repurchases of common stock	(117.1)					(117.1)	(117.1)
Retirement of treasury stock, shares		(8.1)
Retirement of treasury stock	0.0	$ (0.8)	(175.3)			176.1	0.0
Common stock dividends	(322.1)			(322.1)			(322.1)
Stock-based compensation, shares		4.8
Stock-based compensation, Value	87.5	$ 0.5	87.0				87.5
Exercise of stock options, shares		1.9
Exercise of stock options, Value	15.7	$ 0.2	15.5				15.7
Shares withheld for taxes, shares		(1.2)
Shares withheld for taxes, value	(29.2)	$ (0.2)	(29.0)				(29.2)
Other	1.7		0.7	(2.3)			(1.6)	3.3
Balance, shares at Dec. 31, 2018		383.6
Balance at Dec. 31, 2018	$ 2,432.8	$ 38.3	$ 895.9	$ 2,400.1	$ (941.1)	$ 0.0	$ 2,393.2	$ 39.6