Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock, Shares	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss, Net of Tax	Treasury Stock	Total IPG Stockholders' Equity	Noncontrolling Interests
Beginning Balance, Common Stock Shares at Dec. 31, 2013		532.3
Beginning Balance at Dec. 31, 2013	$ 2,250.8		$ 53.0	$ 2,975.2	$ 864.5	$ (411.2)	$ (1,266.3)	$ 2,215.2	$ 35.6
Net income	174.1				168.2			168.2	5.9
Other Comprehensive Income (Loss), Net of Tax	(84.6)					(84.0)		(84.0)	(0.6)
Reclassifications Related to Redeemable Noncontrolling Interests	6.7								6.7
Distributions to noncontrolling interests	(13.9)								(13.9)
Change in redemption value of redeemable noncontrolling interests	3.0				3.0			3.0
Repurchase of common stock, value	(148.1)						(148.1)	(148.1)
Common stock dividends	(119.9)				(119.9)			(119.9)
Stock-based Compensation, Shares		3.3
Stock-based Compensation, Value	51.1		0.3	50.8				51.1
Exercise of Stock Options, Shares		1.0
Exercise of Stock Options, Value	12.0		0.1	11.9				12.0
Shares withheld for taxes, Shares		(0.8)
Shares withheld for taxes, Value	(14.8)		(0.1)	(14.7)				(14.8)
Excess tax benefit from stock-based compensation	4.9			4.9				4.9
Other	(5.4)			(3.7)	(0.6)			(4.3)	(1.1)
Ending Balance, Common Stock Shares at Sep. 30, 2014		535.8
Ending Balance at Sep. 30, 2014	2,115.9		53.3	3,024.4	915.2	(495.2)	(1,414.4)	2,083.3	32.6
Beginning Balance, Common Stock Shares at Dec. 31, 2014		414.6
Beginning Balance at Dec. 31, 2014	2,151.2		41.2	1,547.5	1,183.3	(636.7)	(19.0)	2,116.3	34.9
Net income	197.6				194.3			194.3	3.3
Other Comprehensive Income (Loss), Net of Tax	(192.5)					(189.5)		(189.5)	(3.0)
Reclassifications Related to Redeemable Noncontrolling Interests	4.3								4.3
Distributions to noncontrolling interests	(13.1)								(13.1)
Change in redemption value of redeemable noncontrolling interests	(3.6)				(3.6)			(3.6)
Repurchase of common stock, value	(172.3)						(172.3)	(172.3)
Common stock dividends	(147.2)				(147.2)			(147.2)
Stock-based Compensation, Shares		2.4
Stock-based Compensation, Value	63.4		0.3	63.1				63.4
Exercise of Stock Options, Shares		1.2
Exercise of Stock Options, Value	11.9		0.1	11.8				11.9
Shares withheld for taxes, Shares		(0.8)
Shares withheld for taxes, Value	(17.5)		(0.1)	(17.4)				(17.5)
Excess tax benefit from stock-based compensation	9.0			9.0				9.0
Other	0.4			(0.4)	(0.6)			(1.0)	1.4
Ending Balance, Common Stock Shares at Sep. 30, 2015		417.4
Ending Balance at Sep. 30, 2015	$ 1,891.6		$ 41.5	$ 1,613.6	$ 1,226.2	$ (826.2)	$ (191.3)	$ 1,863.8	$ 27.8