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	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 income (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	(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 income (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	(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
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	237.2
Net income available to IPG common stockholders	238.8				238.8		238.8
Net income attributable to noncontrolling interest	(1.6)							(1.6)
Other comprehensive income (loss)	(39.9)					(37.8)	(37.8)
Other comprehensive loss, attributable to noncontrolling interest								(2.1)
Reclassifications related to redeemable noncontrolling interests	(5.9)							(5.9)
Distributions to noncontrolling interests	(13.7)							13.7
Change in redemption value of redeemable noncontrolling interests	3.1				3.1		3.1
Common stock dividends	(301.8)				(301.8)		(301.8)
Stock-based compensation, shares		3.8
Stock-based compensation, value	64.1		0.4	63.7			64.1
Exercise of stock options, shares		0.0
Exercise of stock options, value	0.5		0.0	0.5			0.5
Shares withheld for taxes, shares		(1.1)
Shares withheld for taxes, value	(22.4)		0.2	22.2			22.4
Other	(8.6)			(8.8)			(8.8)	0.2
Balance at Sep. 30, 2020	2,760.6		38.9	1,028.1	2,623.4	(967.8)	2,722.6	38.0
Common Stock, shares		389.6
Balance at Jun. 30, 2020	2,491.1		38.9	996.3	2,444.3	(1,029.1)	2,450.4	40.7
Net income	278.5
Net income available to IPG common stockholders	279.7				279.7		279.7
Net income attributable to noncontrolling interest	(1.2)							(1.2)
Other comprehensive income (loss)	61.7					61.3	61.3
Other comprehensive loss, attributable to noncontrolling interest								0.4
Reclassifications related to redeemable noncontrolling interests	(2.9)							(2.9)
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	(100.6)				(100.6)		(100.6)
Stock-based compensation, shares		0.2
Stock-based compensation, value	23.1		0.0	23.1			23.1
Exercise of stock options, shares		0.0
Exercise of stock options, value	0.1		0.0	0.1			0.1
Shares withheld for taxes, shares		(0.1)
Shares withheld for taxes, value	(0.2)		(0.0)	0.2			0.2
Other	(8.3)			(8.8)			(8.8)	0.5
Balance at Sep. 30, 2020	$ 2,760.6		$ 38.9	$ 1,028.1	$ 2,623.4	$ (967.8)	$ 2,722.6	$ 38.0
Common Stock, shares		389.7