Segment Information - Revenue, Properties and Outsourcing Assets by Geographic Segment (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 757.6	$ 688.3	$ 2,207.2	$ 2,064.1
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	418.9	313.2	1,144.5	905.0
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	72.4	82.0	272.0	277.7
Other foreign
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 266.3	$ 293.1	$ 790.7	$ 881.4