Share-Based Compensation Plans - Outstanding Restricted Stock Unit Awards (Detail) - Restricted Stock Unit Awards - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
NUMBER
Balance at beginning of period (in shares)	3,399,438
Granted (in shares)	815,314
Distributed (in shares)	(1,016,846)
Forfeited (in shares)	(76,064)
Balance at end of period (in shares)	3,121,842
Units Convertible, at the end of year (in shares)	144,722
AGGREGATE INTRINSIC VALUE
AGGREGATE INTRINSIC VALUE	$ 261.0	$ 339.6
Units Convertible, at the end of year	$ 12.1