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	Total IPG Stockholders' Equity	Noncontrolling Interests
Common Stock, shares		383.6
Changes related to lease standard update	$ 2.2				$ 2.2		$ 2.2
Balance at Dec. 31, 2018	2,432.8		$ 38.3	$ 895.9	2,400.1	$ (941.1)	2,393.2	$ 39.6
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 loss	23.4					23.2	23.2
Other comprehensive 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	(181.4)				(181.4)		(181.4)
Stock-based compensation, shares		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		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 loss	12.1					11.8	11.8
Other comprehensive 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	(90.8)				(90.8)		(90.8)
Stock-based compensation, shares		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		386.4
Common Stock, shares		387.0
Changes related to CECL ASU	(6.6)				(6.6)		(6.6)
Balance at Dec. 31, 2019	2,825.6		38.7	977.3	2,689.9	(930.0)	2,775.9	49.7
Net income	(41.3)
Net income available to IPG common stockholders	(40.9)				(40.9)		(40.9)
Net income attributable to noncontrolling interest	(0.4)							(0.4)
Other comprehensive loss	(101.6)					(99.1)	(99.1)
Other comprehensive loss, attributable to noncontrolling interest								(2.5)
Reclassifications related to redeemable noncontrolling interests	(3.0)							(3.0)
Distributions to noncontrolling interests	(9.4)							9.4
Change in redemption value of redeemable noncontrolling interests	3.1				3.1		3.1
Common stock dividends	(201.2)				(201.2)		(201.2)
Stock-based compensation, shares		3.6
Stock-based compensation, value	41.0		0.4	40.6			41.0
Exercise of stock options, shares		0.0
Exercise of stock options, value	0.4		0.0	0.4			0.4
Shares withheld for taxes, shares		(1.0)
Shares withheld for taxes, value	(22.2)		0.2	22.0			22.2
Other	(0.3)							(0.3)
Balance at Jun. 30, 2020	2,491.1		38.9	996.3	2,444.3	(1,029.1)	2,450.4	40.7
Common Stock, shares		389.5
Balance at Mar. 31, 2020	2,575.2		38.9	981.2	2,591.1	(1,078.7)	2,532.5	42.7
Net income	(43.9)
Net income available to IPG common stockholders	(45.6)				(45.6)		(45.6)
Net income attributable to noncontrolling interest	1.7							1.7
Other comprehensive loss	49.2					49.6	49.6
Other comprehensive loss, attributable to noncontrolling interest								(0.4)
Reclassifications related to redeemable noncontrolling interests	(0.2)							(0.2)
Distributions to noncontrolling interests	(3.8)							3.8
Change in redemption value of redeemable noncontrolling interests	0.0				0.0		0.0
Common stock dividends	(101.2)				(101.2)		(101.2)
Stock-based compensation, shares		0.2
Stock-based compensation, value	15.6		0.1	15.5			15.6
Exercise of stock options, shares		0.0
Exercise of stock options, value	0.2		0.0	0.2			0.2
Shares withheld for taxes, shares		(0.1)
Shares withheld for taxes, value	(0.7)		0.1	0.6			0.7
Other	(0.3)							(0.3)
Balance at Jun. 30, 2020	$ 2,491.1		$ 38.9	$ 996.3	$ 2,444.3	$ (1,029.1)	$ 2,450.4	$ 40.7
Common Stock, shares		389.6