Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Net Income per Share [Abstract]
Net income - Omnicom Group Inc.	$ 1,480.6	$ 1,391.4	$ 1,316.5
Weighted average shares (millions):
Basic	196.4	199.4	205.6
Dilutive stock options and restricted shares	2.2	2.0	1.4
Diluted	198.6	201.4	207.0
Anti-dilutive stock options and restricted shares (millions):	0.0	0.0	4.3
Net income per share - Omnicom Group Inc.:
Basic	$ 7.54	$ 6.98	$ 6.40
Diluted	$ 7.46	$ 6.91	$ 6.36

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