Consolidated Statements of Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Revenue	$ 3,426.9	$ 3,406.9
Salary and service costs	2,545.0	2,533.3
Occupancy and other costs	291.6	309.6
Cost of services	2,836.6	2,842.9
Selling, general and administrative expenses	71.6	86.8
Depreciation and amortization	53.3	57.0
Operating Expenses	2,961.5	2,986.7
Operating Profit	465.4	420.2
Interest Expense	53.8	58.5
Interest Income	6.3	12.7
Income Before Income Taxes and Income (Loss) From Equity Method Investments	417.9	374.4
Income Tax Expense	111.9	97.4
Income (Loss) From Equity Method Investments	0.0	(5.3)
Net Income	306.0	271.7
Net Income Attributed To Noncontrolling Interests	18.2	13.6
Net Income - Omnicom Group Inc.	$ 287.8	$ 258.1
Net Income Per Share - Omnicom Group Inc.:
Basic	$ 1.33	$ 1.19
Diluted	$ 1.33	$ 1.19