Property, Equipment, and Software - Schedule of Property, Equipment and Software (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	$ 229.8	$ 218.8
Less accumulated depreciation and amortization	(113.1)	(101.9)
Property, equipment and software, net	116.7	116.9
Buildings and land
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	4.6	4.6
Computer and other equipment
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	56.4	50.7
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	30.7	31.1
Software
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	129.5	123.0
Office furniture
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	$ 8.6	$ 9.4