Reconciliation of Beginning and Ending Amounts of 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 the year	$ 30.7	$ 21.2	$ 22.9
Additions for tax positions related to the current year	5.5	6.5	11.2
Additions for tax positions related to prior years	0.3	3.0
Reductions for tax positions related to prior years	(4.2)
Reductions related to settlements			(5.7)
Lapse of statute of limitations	(7.8)		(7.2)
Balance at the end of the year	$ 24.5	$ 30.7	$ 21.2