Segment Reporting - Federal Government Segment Revenues by Customer Type (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenue from External Customer [Line Items]
Revenues	$ 4,450.6	$ 4,581.1	$ 4,009.5
Federal Government Business
Revenue from External Customer [Line Items]
Revenues	1,276.2	1,145.4	1,082.4
Federal Government Business | Department of Defense and Intelligence Agencies
Revenue from External Customer [Line Items]
Revenues	614.6	606.3	589.7
Federal Government Business | Federal Civilian
Revenue from External Customer [Line Items]
Revenues	621.6	503.4	421.8
Federal Government Business | Other
Revenue from External Customer [Line Items]
Revenues	$ 40.0	$ 35.7	$ 70.9