Consolidated Statements of Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Revenue	$ 3,629.6	$ 3,587.4
Salary and service costs	2,712.8	2,688.4
Occupancy and other costs	320.3	302.0
Cost of services	3,033.1	2,990.4
Selling, general and administrative expenses	105.4	108.6
Depreciation and amortization	69.4	72.7
Operating Expenses	3,207.9	3,171.7
Operating Profit	421.7	415.7
Interest Expense	62.3	59.3
Interest Income	15.4	13.9
Income Before Income Taxes and Income From Equity Method Investments	374.8	370.3
Income Tax Expense	90.9	108.0
Income From Equity Method Investments	0.8	0.1
Net Income	284.7	262.4
Net Income Attributed To Noncontrolling Interests	20.6	20.6
Net Income - Omnicom Group Inc.	$ 264.1	$ 241.8
Net Income Per Share - Omnicom Group Inc.:
Basic	$ 1.15	$ 1.03
Diluted	1.14	1.02
Dividends Declared Per Common Share	$ 0.60	$ 0.55