Net Income per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Net Income Available for Common Shares:
Net income - Omnicom Group Inc.	$ 241.8	$ 218.4
Net income allocated to participating securities	(0.5)	(1.5)
Net income available for common shares	$ 241.3	$ 216.9
Weighted Average Shares:
Basic	234.6	240.0
Dilutive stock options and restricted shares	1.9	1.1
Diluted	236.5	241.1
Anti-dilutive stock options and restricted shares	1.0	0.1
Net Income per Common Share - Omnicom Group Inc.:
Basic	$ 1.03	$ 0.90
Diluted	$ 1.02	$ 0.90

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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