Commitments and Contingencies - Components of Lease Expense (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Lease Cost [Abstract]
Operating lease cost	$ 22.6	$ 47.2
Variable lease cost	9.4	18.7
Short-term lease cost	1.9	2.3
Sublease income	(0.3)	(0.6)
Total lease cost	$ 33.6	$ 67.6