Income Taxes - Reconciliation of Beginning and Ending Amount of Gross Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 43.5	$ 32.7	$ 27.3
Increases for prior years	1.1	9.3	0.9
Increases for the current year	6.8	3.2	6.1
Reductions related to expiration of statutes of limitations and audit settlements	(4.4)	(1.7)	(1.6)
Balance at end of year	$ 47.0	$ 43.5	$ 32.7