Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Net Income per Share [Abstract]
Net Income - Omnicom Group Inc.	$ 371.9	$ 364.5	$ 965.7	$ 886.7
Weighted Average Shares:
Basic	198.1	205.0	199.7	206.2
Dilutive stock options and restricted shares	1.8	1.3	2.3	1.4
Diluted	199.9	206.3	202.0	207.6
Anti-dilutive stock options and restricted shares	0.0	5.1	0.0	4.3
Net Income per Share - Omnicom Group Inc.:
Basic	$ 1.88	$ 1.78	$ 4.84	$ 4.30
Diluted	$ 1.86	$ 1.77	$ 4.78	$ 4.27