Consolidated Statements of Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Revenue	$ 3,714.3	$ 3,719.5	$ 11,203.5	$ 11,097.1
Salary and service costs	2,834.2	2,764.5	8,319.9	8,184.6
Occupancy and other costs	376.8	316.7	1,016.7	924.5
Net gain on disposition of subsidiaries	(178.4)	0.0	(178.4)	0.0
Cost of services	3,032.6	3,081.2	9,158.2	9,109.1
Selling, general and administrative expenses	113.5	99.5	336.3	318.2
Depreciation and amortization	65.9	68.6	202.7	212.4
Operating Expenses	3,212.0	3,249.3	9,697.2	9,639.7
Operating Profit	502.3	470.2	1,506.3	1,457.4
Interest Expense	69.4	65.0	198.1	187.0
Interest Income	12.7	12.6	42.0	38.0
Income Before Income Taxes and Income From Equity Method Investments	445.6	417.8	1,350.2	1,308.4
Income Tax Expense	115.3	132.0	343.0	406.7
Income From Equity Method Investments	1.0	1.1	3.6	2.7
Net Income	331.3	286.9	1,010.8	904.4
Net Income Attributed To Noncontrolling Interests	32.4	23.3	83.6	70.4
Net Income - Omnicom Group Inc.	$ 298.9	$ 263.6	$ 927.2	$ 834.0
Net Income Per Share - Omnicom Group Inc.:
Basic	$ 1.33	$ 1.14	$ 4.08	$ 3.58
Diluted	1.32	1.13	4.06	3.55
Dividends Declared Per Common Share	$ 0.60	$ 0.55	$ 1.80	$ 1.65