Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Revenue	$ 14,692.2	$ 14,289.1	$ 14,289.4
Media and production costs	664.4	725.1
Unbilled fees and costs and contract assets	678.1	529.5
Work in process	1,342.5	1,254.6
Customer advances	1,356.2	1,492.3
North America
Disaggregation of Revenue [Line Items]
Revenue	7,951.0	7,856.0	7,709.7
UNITED STATES
Disaggregation of Revenue [Line Items]
Revenue	7,471.6	7,367.3	7,245.9
Latin America
Disaggregation of Revenue [Line Items]
Revenue	386.8	329.0	296.1
Europe
Disaggregation of Revenue [Line Items]
Revenue	4,266.9	4,010.5	4,219.6
Middle East and Africa
Disaggregation of Revenue [Line Items]
Revenue	309.6	346.7	267.6
Asia-Pacific
Disaggregation of Revenue [Line Items]
Revenue	1,777.9	1,746.9	1,796.4
Advertising & Media
Disaggregation of Revenue [Line Items]
Revenue	7,891.2	7,433.9	7,966.2
Precision Marketing
Disaggregation of Revenue [Line Items]
Revenue	1,473.5	1,426.6	1,205.2
Commerce & Branding
Disaggregation of Revenue [Line Items]
Revenue	853.7	848.1	802.2
Experiential
Disaggregation of Revenue [Line Items]
Revenue	651.4	635.6	536.0
Execution & Support
Disaggregation of Revenue [Line Items]
Revenue	880.8	1,069.9	1,115.9
Public Relations
Disaggregation of Revenue [Line Items]
Revenue	1,578.9	1,552.7	1,398.2
Healthcare
Disaggregation of Revenue [Line Items]
Revenue	$ 1,362.7	$ 1,322.3	$ 1,265.7