Segment Reporting - Segment Reporting Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Revenues	$ 4,450.6	$ 4,581.1	$ 4,009.5
Gross Profit	1,280.0	1,369.6	1,142.4
Operating Income (Loss)	364.1	409.5	350.9
Other Depreciation and Amortization	28.6	26.3	28.0
Amortization	71.7	65.1	55.7
Hosting Arrangement, Service Contract, Implementation Cost, Expense, Amortization	0.7
Commercial Business
Segment Reporting Information [Line Items]
Revenues	3,174.4	3,435.7	2,927.1
Gross Profit	1,017.6	1,126.2	934.9
Operating Income (Loss)	344.1	411.1	355.9
Other Depreciation and Amortization	20.3	16.3	13.9
Amortization	34.8	31.3	25.7
Federal Government Business
Segment Reporting Information [Line Items]
Revenues	1,276.2	1,145.4	1,082.4
Gross Profit	262.4	243.4	207.6
Operating Income (Loss)	99.2	89.1	76.1
Other Depreciation and Amortization	5.7	5.5	8.5
Amortization	$ 36.9	$ 33.8	$ 30.0