Property, Equipment, and Capitalized Software (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment, Net [Abstract]
Property, equipment, and capitalized software, at cost	$ 1,009.3	$ 921.7
Less accumulated depreciation	(790.4)	(714.0)
Property, equipment, and capitalized software, net	218.9	207.7
Depreciation expense	125.4	113.2	$ 97.8
Computer equipment [Member]
Property, Plant and Equipment, Net [Abstract]
Property, equipment, and capitalized software, at cost	96.9	108.6
Capitalized software [Member]
Property, Plant and Equipment, Net [Abstract]
Property, equipment, and capitalized software, at cost	745.1	642.0
Furniture and fixtures [Member]
Property, Plant and Equipment, Net [Abstract]
Property, equipment, and capitalized software, at cost	40.0	41.7
Leasehold improvements [Member]
Property, Plant and Equipment, Net [Abstract]
Property, equipment, and capitalized software, at cost	113.9	113.3
Telephone equipment [Member]
Property, Plant and Equipment, Net [Abstract]
Property, equipment, and capitalized software, at cost	1.2	2.3
Construction in progress [Member]
Property, Plant and Equipment, Net [Abstract]
Property, equipment, and capitalized software, at cost	$ 12.2	$ 13.8