Consolidated Statements of Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Revenue	$ 3,468.9	$ 3,629.6
Salary and service costs	2,567.6	2,712.8
Occupancy and other costs	309.2	320.3
Cost of services	2,876.8	3,033.1
Selling, general and administrative expenses	103.6	105.4
Depreciation and amortization	59.6	69.4
Operating Expenses	3,040.0	3,207.9
Operating Profit	428.9	421.7
Interest Expense	63.0	62.3
Interest Income	17.0	15.4
Income Before Income Taxes and Income (Loss) From Equity Method Investments	382.9	374.8
Income Tax Expense	102.7	90.9
Income (Loss) From Equity Method Investments	(0.5)	0.8
Net Income	279.7	284.7
Net Income Attributed To Noncontrolling Interests	16.5	20.6
Net Income - Omnicom Group Inc.	$ 263.2	$ 264.1
Net Income Per Share - Omnicom Group Inc.:
Basic	$ 1.18	$ 1.15
Diluted	1.17	1.14
Dividends Declared Per Common Share	$ 0.65	$ 0.60