Share-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Options Activity
Options issued	0	0	0
Options issued	$ 3	$ 8	$ 9
Options vested in period	0
Income tax benefit	$ 9	11	$ 7
Employee Stock Option
Options Activity
Cash received from the exercise of options	2	9
Income tax benefit	$ 1	$ 2
Stock Option
Options Activity
Outstanding at beginning of year	204,434	415,960	956,502
Options issued	0	0	0
Shares, Exercised	(47,393)	(209,976)	(540,542)
Shares, Forfeited	0	0	0
Shares, Expired	(2,490)	(1,550)	0
Shares, Outstanding at end of period	154,551	204,434	415,960
Shares, Exercisable at end of period	154,551	204,434	415,960
Weighted-average grant date fair value at beginning of year	$ 35.96	$ 36.66	$ 40.19	$ 42.77
Weighted-Average Exercise Price, Granted	0	0	0
Weighted-average exercise price, Exercised (in USD per share)	38.60	43.53	44.76
Weighted-average exercise price, Forfeited (in USD per share)	0	0	0
Weighted-average exercise price, Expired (in USD per share)	43.35	51.62	0
Weighted-average grant date fair value at end of year	35.96	36.66	40.19	$ 42.77
Weighted-average exercise price, Exercisable at end of year (in USD per share)	$ 35.96	$ 36.66	$ 40.19
Aggregate intrinsic value, Outstanding		$ 4
Aggregate intrinsic value, Exercisable		$ 4
Weighted-average remaining contractual term, Outstanding		1 year 3 months 25 days
Weighted-average remaining contractual term, Exercisable		1 year 3 months 25 days
Intrinsic value for options exercised	$ 2	$ 10	$ 15