Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Net Income per Share [Abstract]
Net Income - Omnicom Group Inc.	$ 257.6	$ 328.1	$ 545.3	$ 646.7
Weighted Average Shares (millions):
Basic	194.9	195.9	195.8	196.9
Dilutive stock options and restricted shares	1.1	2.6	1.3	2.4
Diluted	196.0	198.5	197.1	199.3
Anti-dilutive stock options and restricted shares (millions)	6.5	0.0	5.8	0.0
Net Income per Share - Omnicom Group Inc.:
Basic	$ 1.32	$ 1.67	$ 2.78	$ 3.28
Diluted	$ 1.31	$ 1.65	$ 2.77	$ 3.24