Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Net Income per Share [Abstract]
Net Income - Omnicom Group Inc.	$ 348.4	$ 348.2	$ 522.2	$ 636.0
Weighted Average Shares:
Basic	205.3	215.4	206.8	215.5
Dilutive stock options and restricted shares	1.6	1.7	1.5	1.5
Diluted	206.9	217.1	208.3	217.0
Anti-dilutive stock options and restricted shares	4.4	0.7	4.4	0.7
Net Income per Share - Omnicom Group Inc.:
Basic	$ 1.70	$ 1.62	$ 2.53	$ 2.95
Diluted	$ 1.68	$ 1.60	$ 2.51	$ 2.93