Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Income Statement [Abstract]
Revenue	$ 4,037.1	$ 3,882.6	$ 11,743.1	$ 11,366.9
Salary and service costs	2,921.5	2,796.0	8,600.4	8,288.7
Occupancy and other costs	322.7	325.6	963.2	953.9
Repositioning costs	38.6	0.0	127.4	57.8
Cost of services	3,282.8	3,121.6	9,691.0	9,300.4
Selling, general and administrative expenses	163.5	99.5	451.8	295.8
Depreciation and amortization	60.7	61.4	178.4	181.4
Total Operating Expenses	3,507.0	3,282.5	10,321.2	9,777.6
Operating Income	530.1	600.1	1,421.9	1,589.3
Interest Expense	60.4	66.4	182.1	182.9
Interest Income	17.2	26.0	68.8	74.0
Income Before Income Taxes and Income From Equity Method Investments	486.9	559.7	1,308.6	1,480.4
Income Tax Expense	132.3	150.2	373.5	389.9
Income From Equity Method Investments	5.8	0.4	6.5	4.6
Net Income	360.4	409.9	941.6	1,095.1
Net Income Attributed To Noncontrolling Interests	19.1	24.0	55.0	62.5
Net Income - Omnicom Group Inc.	$ 341.3	$ 385.9	$ 886.6	$ 1,032.6
Net Income Per Share - Omnicom Group Inc.:
Basic	$ 1.76	$ 1.97	$ 4.54	$ 5.25
Diluted	$ 1.75	$ 1.95	$ 4.51	$ 5.19
Weighted Average Shares:
Basic	193.8	195.6	195.2	196.5
Diluted	194.9	198.2	196.4	198.9