Consolidated Statements of Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Revenue	$ 13,171.1	$ 14,953.7	$ 15,290.2
Salary and service costs	9,572.8	10,972.2	11,306.1
Occupancy and other costs	1,138.5	1,221.8	1,309.6
COVID-19 repositioning costs	277.9	0.0	0.0
Net gain from disposition of subsidiaries	0.0	0.0	(178.4)
Cost of services	10,989.2	12,194.0	12,437.3
Selling, general and administrative expenses	360.5	405.9	455.4
Depreciation and amortization	222.6	231.5	264.0
Operating Expenses	11,572.3	12,831.4	13,156.7
Operating Profit	1,598.8	2,122.3	2,133.5
Interest Expense	221.8	244.3	266.4
Interest Income	32.3	60.3	57.2
Income Before Income Taxes and Income (Loss) From Equity Method Investments	1,409.3	1,938.3	1,924.3
Income Tax Expense	381.7	504.4	492.7
Income (Loss) From Equity Method Investments	(6.8)	2.0	8.9
Net Income	1,020.8	1,435.9	1,440.5
Net Income Attributed To Noncontrolling Interests	75.4	96.8	114.1
Net Income - Omnicom Group Inc.	$ 945.4	$ 1,339.1	$ 1,326.4
Net Income Per Share - Omnicom Group Inc.:
Basic	$ 4.38	$ 6.09	$ 5.85
Diluted	$ 4.37	$ 6.06	$ 5.83