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
Common Stock, shares		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 loss	(99.8)					(97.5)		(97.5)
Other comprehensive 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
Repurchases of common stock	(117.1)						117.1	117.1
Common stock dividends ($0.235 and $0.210 per share, respectively)	(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 at Sep. 30, 2018	2,170.2		39.1	1,041.8	2,158.4	(925.3)	(176.1)	2,137.9	32.3
Common Stock, shares		390.5
Balance at Jun. 30, 2018	2,091.6		39.0	1,022.9	2,076.7	(903.4)	(173.5)	2,061.7	29.9
Net income	163.5
Net income available to IPG common stockholders	161.0				161.0			161.0
Net income attributable to noncontrolling interest	2.5								2.5
Other comprehensive loss	(22.4)					(21.9)		(21.9)
Other comprehensive loss, attributable to noncontrolling interest									(0.5)
Reclassifications related to redeemable noncontrolling interests	0.8								(0.8)
Distributions to noncontrolling interests	(2.8)								2.8
Change in redemption value of redeemable noncontrolling interests	1.6				1.6			1.6
Repurchases of common stock	(2.6)						2.6	2.6
Common stock dividends ($0.235 and $0.210 per share, respectively)	(80.4)				(80.4)			(80.4)
Stock-based compensation, shares		0.1
Stock-based compensation, value	15.3		0.0	15.3				15.3
Exercise of stock options, shares		0.5
Exercise of stock options, value	2.2		0.1	2.1				2.2
Shares withheld for taxes, shares		0.0
Shares withheld for taxes, value	(0.4)		(0.0)	0.4				0.4
Other	(3.8)			(1.9)	0.5			(1.4)	(2.4)
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
Common Stock, shares		391.1
Common Stock, shares		383.6
Balance at Dec. 31, 2018	2,432.8		38.3	895.9	2,400.1	(941.1)		2,393.2	39.6
Cumulative effect of accounting change	2.2				2.2			2.2
Net income	331.7
Net income available to IPG common stockholders	327.1				327.1			327.1
Net income attributable to noncontrolling interest	4.6								4.6
Other comprehensive loss	(26.3)					(25.1)		(25.1)
Other comprehensive loss, attributable to noncontrolling interest									(1.2)
Reclassifications related to redeemable noncontrolling interests	(2.0)								(2.0)
Distributions to noncontrolling interests	(12.4)								12.4
Change in redemption value of redeemable noncontrolling interests	1.4				1.4			1.4
Common stock dividends ($0.235 and $0.210 per share, respectively)	(272.2)				(272.2)			(272.2)
Stock-based compensation, shares		3.7
Stock-based compensation, value	64.7		0.4	64.3				64.7
Exercise of stock options, shares		0.6
Exercise of stock options, value	4.3		0.1	4.2				4.3
Shares withheld for taxes, shares		(1.0)
Shares withheld for taxes, value	(22.5)		0.1	22.4				22.5
Other	2.6			1.0	3.1			4.1	(1.5)
Balance at Sep. 30, 2019	2,503.1		38.7	941.0	2,455.5	(966.2)		2,469.0	34.1
Common Stock, shares		386.4
Balance at Jun. 30, 2019	2,458.4		38.6	921.4	2,381.8	(917.9)		2,423.9	34.5
Net income	168.4
Net income available to IPG common stockholders	165.6				165.6			165.6
Net income attributable to noncontrolling interest	2.8								2.8
Other comprehensive loss	(49.7)					(48.3)		(48.3)
Other comprehensive loss, attributable to noncontrolling interest									(1.4)
Reclassifications related to redeemable noncontrolling interests	(2.4)								(2.4)
Distributions to noncontrolling interests	(4.3)								4.3
Change in redemption value of redeemable noncontrolling interests	0.0				0.0			0.0
Common stock dividends ($0.235 and $0.210 per share, respectively)	(90.8)				(90.8)			(90.8)
Stock-based compensation, shares		0.1
Stock-based compensation, value	16.2		0.0	16.2				16.2
Exercise of stock options, shares		0.5
Exercise of stock options, value	3.7		0.1	3.6				3.7
Shares withheld for taxes, shares		(0.1)
Shares withheld for taxes, value	(0.2)		(0.0)	0.2				0.2
Other	1.0			(0.0)	1.1			1.1	(0.1)
Balance at Sep. 30, 2019	$ 2,503.1		$ 38.7	$ 941.0	$ 2,455.5	$ (966.2)		$ 2,469.0	$ 34.1
Common Stock, shares		386.9