Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Net Income per Share [Abstract]
Net Income - Omnicom Group Inc.	$ 227.5	$ 173.8
Weighted Average Shares:
Basic	202.2	208.3
Dilutive stock options and restricted shares	2.3	1.5
Diluted	204.5	209.8
Anti-dilutive stock options and restricted shares	0.0	0.5
Net Income per Share - Omnicom Group Inc.:
Basic	$ 1.13	$ 0.83
Diluted	$ 1.11	$ 0.83