Commitments and Contingencies - Components of Lease Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lease Cost [Abstract]
Operating lease cost	$ 89.3	$ 94.4
Variable lease cost	32.7	32.4
Sublease income	(1.7)	(1.2)
Total lease cost	$ 120.3	$ 125.6