Share-Based Compensation Plans - Outstanding Restricted Stock Unit Awards (Detail) - Restricted Stock Unit Awards $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) shares
NUMBER
Restricted Stock Unit Awards Outstanding, at beginning of the year (in shares)	3,695,657
Granted (in shares)	863,308
Distributed (in shares)	(1,040,725)
Forfeited (in shares)	(118,802)
Stock and Stock Unit Awards Outstanding, at the end of year (in shares)	3,399,438
Units Convertible, at the end of year (in shares)	168,111
AGGREGATE INTRINSIC VALUE
Restricted Stock Unit Awards Outstanding, at beginning of the year | $	$ 329.1
Stock and Stock Unit Awards Outstanding, at the end of year | $	339.6
Units Convertible, at the end of year | $	$ 16.8