Consolidated Statements of Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Statement [Abstract]
Revenue	$ 3,406.9	$ 3,468.9
Salary and service costs	2,533.3	2,567.6
Occupancy and other costs	309.6	309.2
Cost of services	2,842.9	2,876.8
Selling, general and administrative expenses	86.8	103.6
Depreciation and amortization	57.0	59.6
Operating Expenses	2,986.7	3,040.0
Operating Profit	420.2	428.9
Interest Expense	58.5	63.0
Interest Income	12.7	17.0
Income Before Income Taxes and Loss From Equity Method Investments	374.4	382.9
Income Tax Expense	97.4	102.7
Loss From Equity Method Investments	(5.3)	(0.5)
Net Income	271.7	279.7
Net Income Attributed To Noncontrolling Interests	13.6	16.5
Net Income - Omnicom Group Inc.	$ 258.1	$ 263.2
Net Income Per Share - Omnicom Group Inc.:
Basic	$ 1.19	$ 1.18
Diluted	$ 1.19	$ 1.17