Segment Reporting Revenue by Customer Type (details) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Revenue from External Customer [Line Items]
Revenues	$ 1,116.8	$ 1,197.9	$ 3,376.5	$ 3,430.7
Department of Defense and Intelligence Agencies
Revenue from External Customer [Line Items]
Revenues	164.8	165.5	452.7	458.4
Federal Civilian
Revenue from External Customer [Line Items]
Revenues	159.5	124.8	468.3	361.9
Other
Revenue from External Customer [Line Items]
Revenues	$ 10.1	$ 7.6	$ 29.7	$ 26.9