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, Issued		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	131.7
Net income available to IPG common stockholders	131.7				131.7			131.7
Net income attributable to noncontrolling interest	0.0								0.0
Other comprehensive income (loss)	(77.4)					(75.6)		(75.6)
Other comprehensive income (loss), attributable to noncontrolling interest									(1.8)
Reclassifications related to redeemable noncontrolling interests	6.3								6.3
Distributions to noncontrolling interests	(10.6)								(10.6)
Change in redemption value of redeemable noncontrolling interests	44.7			41.8	2.9			44.7
Repurchases of common stock	(114.5)						114.5	114.5
Common stock dividends ($0.235 and $0.210 per share, respectively)	(161.2)				(161.2)			(161.2)
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture		4.6
Stock-based compensation, value	48.5		0.5	48.0				48.5
Exercise of stock options, shares		0.9
Exercise of stock options, value	(7.0)		(0.0)	(7.0)				(7.0)
Shares withheld for taxes, shares		(1.2)
Shares withheld for taxes, value	(28.6)		0.1	28.5				28.6
Other	0.6			0.6	1.2			1.8	(1.2)
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
Common Stock, Shares, Issued		390.3
Balance at Mar. 31, 2018	2,140.3		39.0	963.7	2,010.5	(790.8)	(113.9)	2,108.5	31.8
Net income	147.8
Net income available to IPG common stockholders	145.8				145.8			145.8
Net income attributable to noncontrolling interest	2.0								2.0
Other comprehensive income (loss)	(114.7)					(112.6)		(112.6)
Other comprehensive income (loss), attributable to noncontrolling interest									(2.1)
Reclassifications related to redeemable noncontrolling interests	3.8								3.8
Distributions to noncontrolling interests	(6.7)								(6.7)
Change in redemption value of redeemable noncontrolling interests	43.2			41.8	1.4			43.2
Repurchases of common stock	(59.6)						59.6	59.6
Common stock dividends ($0.235 and $0.210 per share, respectively)	(80.4)				(80.4)			(80.4)
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture		0.2
Stock-based compensation, value	17.8		0.1	17.7				17.8
Exercise of stock options, shares		0.1
Exercise of stock options, value	(0.0)		(0.1)	(0.1)				(0.0)
Shares withheld for taxes, shares		(0.1)
Shares withheld for taxes, value	(0.5)		(0.0)	0.5				0.5
Other	(0.6)			(0.1)	0.6			0.5	(1.1)
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
Common Stock, Shares, Issued		390.5
Common Stock, Shares, Issued		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	163.3
Net income available to IPG common stockholders	161.5				161.5			161.5
Net income attributable to noncontrolling interest	1.8								1.8
Other comprehensive income (loss)	23.4					23.2		23.2
Other comprehensive income (loss), attributable to noncontrolling interest									0.2
Reclassifications related to redeemable noncontrolling interests	(0.4)								(0.4)
Distributions to noncontrolling interests	(8.1)								(8.1)
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)	(181.4)				(181.4)			(181.4)
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture		3.6
Stock-based compensation, value	48.5		0.4	48.1				48.5
Exercise of stock options, shares		0.1
Exercise of stock options, value	(0.6)		(0.0)	(0.6)				(0.6)
Shares withheld for taxes, shares		(0.9)
Shares withheld for taxes, value	(22.3)		0.1	22.2				22.3
Other	1.6			1.0	2.0			3.0	(1.4)
Balance at Jun. 30, 2019	2,458.4		38.6	921.4	2,381.8	(917.9)		2,423.9	34.5
Common Stock, Shares, Issued		386.2
Balance at Mar. 31, 2019	2,354.6		38.6	903.3	2,303.1	(929.7)		2,315.3	39.3
Net income	172.8
Net income available to IPG common stockholders	169.5				169.5			169.5
Net income attributable to noncontrolling interest	3.3								3.3
Other comprehensive income (loss)	12.1					11.8		11.8
Other comprehensive income (loss), attributable to noncontrolling interest									0.3
Reclassifications related to redeemable noncontrolling interests	(3.0)								(3.0)
Distributions to noncontrolling interests	(5.6)								(5.6)
Change in redemption value of redeemable noncontrolling interests	1.1				1.1			1.1
Common stock dividends ($0.235 and $0.210 per share, respectively)	(90.8)				(90.8)			(90.8)
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture		0.2
Stock-based compensation, value	18.4		0.1	18.3				18.4
Exercise of stock options, shares		0.1
Exercise of stock options, value	(0.0)		(0.0)	(0.0)				(0.0)
Shares withheld for taxes, shares		(0.1)
Shares withheld for taxes, value	(0.3)		0.1	0.2				0.3
Other	0.9			(0.0)	1.1			1.1	(0.2)
Balance at Jun. 30, 2019	$ 2,458.4		$ 38.6	$ 921.4	$ 2,381.8	$ (917.9)		$ 2,423.9	$ 34.5
Common Stock, Shares, Issued		386.4