Consolidated Statements of Income - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Revenue	$ 2,800,700,000	$ 3,719,800,000	$ 6,207,600,000	$ 7,188,700,000
Salary and service costs	2,031,100,000	2,665,200,000	4,564,400,000	5,232,800,000
Occupancy and other costs	290,000,000.0	315,400,000	599,600,000	624,700,000
Repositioning costs and net loss on dispositions	277,900,000	0	277,900,000	0
Cost of services	2,599,000,000.0	2,980,600,000	5,441,900,000	5,857,500,000
Selling, general and administrative expenses	82,100,000	107,700,000	168,900,000	211,200,000
Depreciation and amortization	57,100,000	57,800,000	114,100,000	117,400,000
Operating Expenses	2,738,200,000	3,146,100,000	5,724,900,000	6,186,100,000
Operating Profit	62,500,000	573,700,000	482,700,000	1,002,600,000
Interest Expense	53,700,000	66,600,000	112,200,000	129,600,000
Interest Income	6,500,000	16,400,000	19,200,000	33,400,000
Income Before Income Taxes and Income (Loss) From Equity Method Investments	15,300,000	523,500,000	389,700,000	906,400,000
Income Tax Expense	21,900,000	130,600,000	119,300,000	233,200,000
Income (Loss) From Equity Method Investments	(7,800,000)	1,200,000	(13,000,000.0)	700,000
Net Income (Loss)	(14,400,000)	394,100,000	257,400,000	673,900,000
Net Income Attributed To Noncontrolling Interests	9,800,000	23,400,000	23,400,000	40,000,000.0
Net Income (Loss) - Omnicom Group Inc.	$ (24,200,000)	$ 370,700,000	$ 234,000,000.0	$ 633,900,000
Net Income (Loss) Per Share - Omnicom Group Inc.:
Basic	$ (0.11)	$ 1.69	$ 1.08	$ 2.86
Diluted	$ (0.11)	$ 1.68	$ 1.08	$ 2.85