Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net Income	$ 394.1	$ 394.8	$ 673.9	$ 679.5
Cash flow hedge:
Amortization of loss included in interest expense	1.4	1.4	2.8	2.8
Income tax effect	(0.4)	(0.4)	(0.8)	(0.8)
Other comprehensive income	1.0	1.0	2.0	2.0
Defined benefit pension plans and postemployment arrangements:
Amortization of prior service cost	1.3	1.9	2.6	3.9
Amortization of actuarial losses	0.5	2.2	1.0	4.2
Income tax effect	(0.9)	(1.3)	(1.6)	(2.4)
Other comprehensive income	0.9	2.8	2.0	5.7
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	(18.8)	(325.8)	12.9	(237.1)
Other Comprehensive Income	(16.9)	(322.0)	16.9	(229.1)
Comprehensive Income	377.2	72.8	690.8	450.4
Comprehensive Income Attributed To Noncontrolling Interests	23.4	0.9	41.0	26.5
Comprehensive Income - Omnicom Group Inc.	$ 353.8	$ 71.9	$ 649.8	$ 423.9