Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Net Income per Share [Abstract]
Net Income - Omnicom Group Inc.	$ 328.1	$ 366.3	$ 646.7	$ 593.8
Weighted Average Shares (millions):
Basic	195.9	198.9	196.9	200.6
Dilutive stock options and restricted shares	2.6	2.7	2.4	2.5
Diluted	198.5	201.6	199.3	203.1
Net Income per Share - Omnicom Group Inc.:
Basic	$ 1.67	$ 1.84	$ 3.28	$ 2.96
Diluted	$ 1.65	$ 1.82	$ 3.24	$ 2.92