Segment Information - Revenue, Properties and Outsourcing Assets by Geographic Segment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 488.0	$ 495.2	$ 1,515.1	$ 1,449.4
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	191.1	193.6	627.2	584.0
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	53.1	58.6	225.2	176.9
Other foreign
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 243.8	$ 243.0	$ 662.7	$ 688.5