Consolidated Statements of Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Revenue	$ 3,206.5	$ 3,623.8	$ 9,414.1	$ 10,812.5
Salary and service costs	2,287.1	2,704.7	6,851.5	7,937.5
Occupancy and other costs	273.1	290.7	872.6	915.4
Repositioning costs and net loss on dispositions	0.0	0.0	277.9	0.0
Cost of services	2,560.2	2,995.4	8,002.0	8,852.9
Selling, general and administrative expenses	90.2	97.2	259.2	308.4
Depreciation and amortization	54.7	57.9	168.8	175.3
Operating Expenses	2,705.1	3,150.5	8,430.0	9,336.6
Operating Profit	501.4	473.3	984.1	1,475.9
Interest Expense	54.4	62.8	166.6	192.4
Interest Income	5.9	13.5	25.1	46.9
Income Before Income Taxes and Income (Loss) From Equity Method Investments	452.9	424.0	842.6	1,330.4
Income Tax Expense	120.9	112.3	240.2	345.5
Income (Loss) From Equity Method Investments	2.9	0.5	(10.1)	1.2
Net Income	334.9	312.2	592.3	986.1
Net Income Attributed To Noncontrolling Interests	21.6	22.0	45.0	62.0
Net Income - Omnicom Group Inc.	$ 313.3	$ 290.2	$ 547.3	$ 924.1
Net Income Per Share - Omnicom Group Inc.:
Basic	$ 1.45	$ 1.33	$ 2.54	$ 4.19
Diluted	$ 1.45	$ 1.32	$ 2.53	$ 4.17