Share-Based Compensation Plans - Outstanding Restricted Stock Unit Awards (Detail) - Restricted Stock Unit Awards - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
NUMBER
Balance at beginning of period (in shares)	2,145,651
Granted (in shares)	846,433
Distributed (in shares)	(944,393)
Forfeited (in shares)	(46,175)
Balance at end of period (in shares)	2,001,516
Units Convertible, at the end of year (in shares)	19,526
AGGREGATE INTRINSIC VALUE
AGGREGATE INTRINSIC VALUE	$ 239.4	$ 199.8
Units Convertible, at the end of year	$ 2.3