Consolidated Statements of Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Revenue	$ 3,571.6	$ 2,800.7	$ 6,998.6	$ 6,207.6
Salary and service costs	2,603.1	2,031.1	5,148.1	4,564.4
Occupancy and other costs	293.9	290.0	585.5	599.6
Gain on disposition of subsidiary	(50.5)	0.0	(50.5)	0.0
COVID-19 repositioning costs	0.0	277.9	0.0	277.9
Cost of services	2,846.5	2,599.0	5,683.1	5,441.9
Selling, general and administrative expenses	103.2	82.1	174.9	168.9
Depreciation and amortization	53.5	57.1	106.8	114.1
Operating Expenses	3,003.2	2,738.2	5,964.8	5,724.9
Operating Profit	568.4	62.5	1,033.8	482.7
Interest Expense	80.3	53.7	134.1	112.2
Interest Income	6.8	6.5	13.1	19.2
Income Before Income Taxes and Income (Loss) From Equity Method Investments	494.9	15.3	912.8	389.7
Income Tax Expense	123.2	21.9	235.2	119.3
Income (Loss) From Equity Method Investments	(0.1)	(7.8)	(0.1)	(13.0)
Net Income (Loss)	371.6	(14.4)	677.5	257.4
Net Income Attributed To Noncontrolling Interests	23.4	9.8	41.5	23.4
Net Income (Loss) - Omnicom Group Inc.	$ 348.2	$ (24.2)	$ 636.0	$ 234.0
Net Income (Loss) Per Share - Omnicom Group Inc.:
Basic	$ 1.62	$ (0.11)	$ 2.95	$ 1.08
Diluted	$ 1.60	$ (0.11)	$ 2.93	$ 1.08