Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net Income	$ 355.1	$ 351.9	$ 617.5	$ 588.2
Cash flow hedge:
Loss for the period	0.0	0.0	0.0	(48.8)
Amortization of loss included in interest expense	1.4	1.2	2.8	1.2
Income tax effect	(0.6)	(0.5)	(1.2)	19.8
Other comprehensive income	0.8	0.7	1.6	(27.8)
Defined benefit pension plans and postemployment arrangements:
Amortization of prior service cost included in periodic benefit expense	2.2	1.8	4.2	3.6
Amortization of actuarial losses included in periodic benefit expense	1.7	1.4	3.6	2.9
Income tax effect	(1.9)	(1.4)	(3.6)	(2.4)
Other comprehensive income	2.0	1.8	4.2	4.1
Available-for-sale securities:
Unrealized gain for the period	0.3	0.0	0.5	0.0
Income tax effect	(0.1)	0.0	(0.2)	0.0
Other comprehensive income	0.2	0.0	0.3	0.0
Foreign currency translation adjustment	140.1	(118.3)	254.8	(5.2)
Other Comprehensive Income	143.1	(115.8)	260.9	(28.9)
Comprehensive Income	498.2	236.1	878.4	559.3
Comprehensive Income Attributed To Noncontrolling Interests	28.5	22.2	63.9	60.9
Comprehensive Income - Omnicom Group Inc.	$ 469.7	$ 213.9	$ 814.5	$ 498.4