Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Net Income per Share [Abstract]
Net income - Omnicom Group Inc.	$ 1,391.4	$ 1,316.5	$ 1,407.8
Weighted average shares (millions):
Basic	199.4	205.6	214.3
Dilutive stock options and restricted shares	2.0	1.4	1.3
Diluted	201.4	207.0	215.6
Anti-dilutive stock options and restricted shares (millions)	0.0	4.3	4.7
Net income per share - Omnicom Group Inc.:
Basic	$ 6.98	$ 6.40	$ 6.57
Diluted	$ 6.91	$ 6.36	$ 6.53