Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Net Income Available for Common Shares:
Net income - Omnicom Group Inc.	$ 258.1	$ 263.2
Weighted Average Shares:
Basic	216.6	223.2
Dilutive stock options and restricted shares	0.9	1.0
Diluted	217.5	224.2
Anti-dilutive stock options and restricted shares	0.9	0.9
Net Income per Share - Omnicom Group Inc.:
Basic	$ 1.19	$ 1.18
Diluted	$ 1.19	$ 1.17

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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