Net Income Per Common Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2014	Mar. 31, 2013
Net Income Available for Common Shares:
Net income - Omnicom Group Inc.	$ 205.5	$ 205.1
Net income allocated to participating securities	(4.1)	(5.4)
Net income available for common shares	$ 201.4	$ 199.7
Weighted Average Shares:
Basic	259.1	261.0
Dilutive stock options, restricted shares and shares issuable for the conversion premium of convertible debt	2.3	2.2
Diluted	261.4	263.2
Anti-dilutive stock options and restricted shares	0.1	0.1
Net Income per Common Share - Omnicom Group Inc.:
Basic	$ 0.78	$ 0.76
Diluted	$ 0.77	$ 0.76

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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