Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Net Income per Share [Abstract]
Net Income - Omnicom Group Inc.	$ 364.5	$ 355.6	$ 886.7	$ 991.6
Weighted Average Shares:
Basic	205.0	214.0	206.2	215.0
Dilutive stock options and restricted shares	1.3	1.4	1.4	1.4
Diluted	206.3	215.4	207.6	216.4
Anti-dilutive stock options and restricted shares	5.1	0.7	4.3	0.7
Net Income per Share - Omnicom Group Inc.:
Basic	$ 1.78	$ 1.66	$ 4.30	$ 4.61
Diluted	$ 1.77	$ 1.65	$ 4.27	$ 4.58