Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Net Income per Share [Abstract]
Net Income - Omnicom Group Inc.	$ 318.6	$ 227.5
Weighted Average Shares (millions):
Basic	197.9	202.2
Dilutive stock options and restricted shares	2.2	2.3
Diluted	200.1	204.5
Net Income per Share - Omnicom Group Inc.:
Basic	$ 1.61	$ 1.13
Diluted	$ 1.59	$ 1.11