Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Net Income per Share [Abstract]
Net Income - Omnicom Group Inc.	$ 173.8	$ 287.8
Weighted Average Shares:
Basic	208.3	215.6
Dilutive stock options and restricted shares	1.5	1.2
Diluted	209.8	216.8
Anti-dilutive stock options and restricted shares	0.5	0.7
Net Income per Share - Omnicom Group Inc.:
Basic	$ 0.83	$ 1.33
Diluted	$ 0.83	$ 1.33