Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
NET INCOME	$ 354.2	$ 673.9	$ 637.7
Foreign Currency Translation:
Foreign currency translation adjustments	39.4	11.3	(149.6)
Reclassification adjustments recognized in net income	20.0	6.7	15.7
Foreign currency translation, net of tax	59.4	18.0	(133.9)
Derivatives instruments:
Changes in fair value of derivative instruments	11.3	0.0	0.0
Recognition of previously unrealized losses included in net income	2.4	2.3	2.2
Income tax effect	(3.4)	(0.5)	(0.7)
Derivative instruments, net of tax	10.3	1.8	1.5
Defined benefit pension and other postretirement plans:
Net actuarial (losses) gains for the period	(29.2)	(14.8)	12.6
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	7.4	6.7	7.5
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment	(0.1)	0.0	(1.0)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Other, before Tax	(3.3)	(2.5)	(1.0)
Income tax effect	4.6	1.2	(1.8)
Defined benefit pension and other postretirement plans, net of tax	(20.6)	(9.4)	16.3
Other comprehensive income (loss), net of tax	49.1	10.4	(116.1)
Total comprehensive income	403.3	684.3	521.6
Less: comprehensive income attributable to noncontrolling interests	2.4	17.2	16.0
Comprehensive Income Attributable to IPG	$ 400.9	$ 667.1	$ 505.6