Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Net Income per Share [Abstract]
Net Income - Omnicom Group Inc.	$ 366.3	$ 348.4	$ 593.8	$ 522.2
Weighted Average Shares:
Basic	198.9	205.3	200.6	206.8
Dilutive stock options and restricted shares	2.7	1.6	2.5	1.5
Diluted	201.6	206.9	203.1	208.3
Anti-dilutive stock options and restricted shares	0.0	4.4	0.0	4.4
Net Income per Share - Omnicom Group Inc.:
Basic	$ 1.84	$ 1.70	$ 2.96	$ 2.53
Diluted	$ 1.82	$ 1.68	$ 2.92	$ 2.51