Segment Reporting Revenue by Customer Type (details) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Revenue from External Customer [Line Items]
Revenues	$ 1,034.7	$ 1,130.9	$ 2,083.7	$ 2,259.7
Federal Government
Revenue from External Customer [Line Items]
Revenues	309.0	319.6	626.5	616.3
Department of Defense and Intelligence Agencies
Revenue from External Customer [Line Items]
Revenues	141.6	155.0	291.7	287.9
Federal Civilian
Revenue from External Customer [Line Items]
Revenues	155.5	155.7	313.3	308.8
Other
Revenue from External Customer [Line Items]
Revenues	$ 11.9	$ 8.9	$ 21.5	$ 19.6