Consolidated Statements of Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Revenue	$ 14,953.7	$ 15,290.2	$ 15,273.6
Salary and service costs	10,972.2	11,306.1	11,227.2
Occupancy and other costs	1,221.8	1,309.6	1,240.8
Net gain from disposition of subsidiaries	0.0	(178.4)	0.0
Cost of services	12,194.0	12,437.3	12,468.0
Selling, general and administrative expenses	405.9	455.4	439.7
Depreciation and amortization	231.5	264.0	282.1
Operating Expenses	12,831.4	13,156.7	13,189.8
Operating Profit	2,122.3	2,133.5	2,083.8
Interest Expense	244.3	266.4	248.6
Interest Income	60.3	57.2	49.7
Income Before Income Taxes and Income From Equity Method Investments	1,938.3	1,924.3	1,884.9
Income Tax Expense	504.4	492.7	696.2
Income From Equity Method Investments	2.0	8.9	3.5
Net Income	1,435.9	1,440.5	1,192.2
Net Income Attributed To Noncontrolling Interests	96.8	114.1	103.8
Net Income - Omnicom Group Inc.	$ 1,339.1	$ 1,326.4	$ 1,088.4
Net Income Per Share - Omnicom Group Inc.:
Basic	$ 6.09	$ 5.85	$ 4.68
Diluted	$ 6.06	$ 5.83	$ 4.65