Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net Income	$ 380.1	$ 334.9	$ 1,057.7	$ 592.3
Cash flow hedge:
Amortization of loss included in interest expense	1.3	1.3	4.2	4.1
Income tax effect	(0.4)	(0.4)	(1.2)	(1.2)
Other comprehensive income (loss), Cash flow hedge	0.9	0.9	3.0	2.9
Defined benefit pension plans and postemployment arrangements:
Amortization of prior service cost	1.1	1.2	3.6	3.7
Amortization of actuarial losses	3.4	1.8	9.9	5.6
Income tax effect	(1.7)	(0.6)	(5.1)	(2.6)
Other comprehensive income (loss), Defined benefit pension plans and postemployment arrangements	2.8	2.4	8.4	6.7
Foreign currency translation adjustment	(132.2)	78.1	(121.1)	(210.3)
Other Comprehensive Income (Loss)	(128.5)	81.4	(109.7)	(200.7)
Comprehensive Income	251.6	416.3	948.0	391.6
Comprehensive Income Attributed To Noncontrolling Interests	16.5	27.0	50.5	27.3
Comprehensive Income - Omnicom Group Inc.	$ 235.1	$ 389.3	$ 897.5	$ 364.3