Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net Income	$ 279.7	$ 284.7
Cash flow hedge:
Amortization of loss included in interest expense	1.4	1.4
Income tax effect	(0.4)	(0.4)
Other comprehensive income	1.0	1.0
Defined benefit pension plans and postemployment arrangements:
Amortization of prior service cost	1.3	2.0
Amortization of actuarial losses	0.5	2.0
Income tax effect	(0.7)	(1.1)
Other comprehensive income	1.1	2.9
Available-for-sale securities:
Reclassification	0.0	0.3
Other comprehensive income	0.0	0.3
Foreign currency translation adjustment	31.7	88.7
Other Comprehensive Income	33.8	92.9
Comprehensive Income	313.5	377.6
Comprehensive Income Attributed To Noncontrolling Interests	17.5	25.6
Comprehensive Income - Omnicom Group Inc.	$ 296.0	$ 352.0