Summary of Significant Accounting Policies - Property and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment	$ 613.6	$ 633.4
Land
Property, Plant and Equipment [Line Items]
Property and equipment	3.4	3.4
Buildings
Property, Plant and Equipment [Line Items]
Property and equipment	$ 12.0	14.5
Buildings | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	40 years
Furniture, fixtures, and autos
Property, Plant and Equipment [Line Items]
Property and equipment	$ 167.3	172.3
Furniture, fixtures, and autos | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	2 years
Furniture, fixtures, and autos | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	15 years
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment	$ 128.7	137.1
Computer equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	2 years
Computer equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	15 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment	$ 302.2	$ 306.1