Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Net Income per Share [Abstract]
Net Income - Omnicom Group Inc.	$ 385.9	$ 371.9	$ 1,032.6	$ 965.7
Weighted Average Shares (millions):
Basic	195.6	198.1	196.5	199.7
Dilutive stock options and restricted shares	2.6	1.8	2.4	2.3
Diluted	198.2	199.9	198.9	202.0
Net Income per Share - Omnicom Group Inc.:
Basic	$ 1.97	$ 1.88	$ 5.25	$ 4.84
Diluted	$ 1.95	$ 1.86	$ 5.19	$ 4.78