Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock, Shares	Common Stock, Amount	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss, Net of Tax	Treasury Stock	Total IPG Stockholders' Equity	Noncontrolling Interests
Balance, common stock 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	301.2
Net income available to IPG common stockholders	302.1				302.1			302.1
Net income attributable to noncontrolling interest	(0.9)								(0.9)
Other comprehensive income (loss)	132.6					132.0		132.0
Other comprehensive income (loss), attributable to noncontrolling interest									0.6
Reclassifications related to redeemable noncontrolling interests	7.3								7.3
Distributions to noncontrolling interests	(17.5)								(17.5)
Change in redemption value of redeemable noncontrolling interests	(4.6)				(4.6)			(4.6)
Repurchase of Common Stock	(216.0)						(216.0)	(216.0)
Common stock dividend	(211.2)				(211.2)			(211.2)
Stock-based compensation, shares		5.6
Stock-based compensation, value	63.5		0.6	62.9				63.5
Exercise of stock options, shares		1.1
Exercise of stock options, value	12.2		0.1	12.1				12.2
Shares withheld for taxes, shares		(1.6)
Shares withheld for taxes, value	(38.7)		(0.2)	(38.5)				(38.7)
Other	(3.4)				(1.1)			(1.1)	(2.3)
Balance, common stock shares at Sep. 30, 2017		399.4
Balance at Sep. 30, 2017	2,115.8		39.9	1,235.7	1,925.1	(832.4)	(279.3)	2,089.0	26.8
Balance, common stock 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	295.2
Net income available to IPG common stockholders	292.7				292.7			292.7
Net income attributable to noncontrolling interest	2.5								2.5
Other comprehensive income (loss)	(99.8)					(97.5)		(97.5)
Other comprehensive income (loss), attributable to noncontrolling interest									(2.3)
Reclassifications related to redeemable noncontrolling interests	7.1								7.1
Distributions to noncontrolling interests	(13.4)								(13.4)
Change in redemption value of redeemable noncontrolling interests	46.3			41.8	4.5			46.3
Repurchase of Common Stock	(117.1)						(117.1)	(117.1)
Common stock dividend	(241.6)				(241.6)			(241.6)
Stock-based compensation, shares		4.7
Stock-based compensation, value	63.8		0.5	63.3				63.8
Exercise of stock options, shares		1.4
Exercise of stock options, value	9.2		0.1	9.1				9.2
Shares withheld for taxes, shares		(1.2)
Shares withheld for taxes, value	(29.0)		(0.1)	(28.9)				(29.0)
Other	3.2			1.3	(1.7)			(0.4)	3.6
Balance, common stock shares at Sep. 30, 2018		391.1
Balance at Sep. 30, 2018	$ 2,170.2		$ 39.1	$ 1,041.8	$ 2,158.4	$ (925.3)	$ (176.1)	$ 2,137.9	$ 32.3