Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Net Income per Share [Abstract]
Net Income - Omnicom Group Inc.	$ 287.7	$ 318.6
Weighted Average Shares (millions):
Basic	196.7	197.9
Dilutive stock options and restricted shares	1.6	2.2
Diluted	198.3	200.1
Anti-dilutive stock options and restricted shares (millions)	1.1	0.0
Net Income per Share - Omnicom Group Inc.:
Basic	$ 1.46	$ 1.61
Diluted	$ 1.45	$ 1.59