Share-Based Compensation - Summary of Activity and Terms of Outstanding Options (Detail) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Options Outstanding (shares) [Roll Forward]
Options outstanding beginning balance	64	312	556
Exercised	(49)	(244)	(237)
Forfeited	0	(4)	(7)
Options outstanding ending balance	15	64	312
Options Outstanding, Weighted Average Exercise Price (dollars per share) [Abstract]
Beginning balance	$ 23.33	$ 22.25	$ 21.72
Exercised	$ 24.21	$ 21.97	$ 21.04
Forfeited	$ 0.00	$ 21.72	$ 21.07
Ending balance	$ 20.49	$ 23.33	$ 22.25
Weighted Average Remaining Contractual Life (years), Options outstanding	9 months 18 days
Aggregate Intrinsic Value, Options outstanding	$ 0.2