Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net Income	$ 312.2	$ 331.3	$ 986.1	$ 1,010.8
Cash flow hedge:
Amortization of loss included in interest expense	0.9	1.4	2.7	4.2
Income tax effect	0.0	(0.4)	0.2	(1.2)
Other comprehensive income	0.9	1.0	2.9	3.0
Defined benefit pension plans and postemployment arrangements:
Amortization of prior service cost	1.3	2.0	3.9	5.9
Amortization of actuarial losses	0.6	2.0	1.6	6.2
Income tax effect	(1.2)	1.5	(2.8)	(0.9)
Other comprehensive income	0.7	5.5	2.7	11.2
Available-for-sale securities:
Reclassification	0.0	0.0	0.0	0.3
Other comprehensive income	0.0	0.0	0.0	0.3
Foreign currency translation adjustment	(129.2)	(30.3)	(116.4)	(267.4)
Other Comprehensive Income	(127.6)	(23.8)	(110.8)	(252.9)
Comprehensive Income	184.6	307.5	875.3	757.9
Comprehensive Income Attributed To Noncontrolling Interests	8.3	27.5	49.2	53.9
Comprehensive Income - Omnicom Group Inc.	$ 176.3	$ 280.0	$ 826.1	$ 704.0