Share-Based Compensation - Stock Options Status and Activity (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Aggregate Intrinsic Value, Exercised	$ 1	$ 6	$ 11
Stock Option
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares Under Option Outstanding Beginning Balance (in shares)	318,016
Granted (in shares)	0
Exercised (in shares)	(21,823)
Forfeited (in shares)	(2,196)
Shares Under Option Outstanding Ending Balance (in shares)	293,997	318,016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted Average Exercise Prices, Outstanding, Beginning Balance (in dollars per share)	$ 46.18
Granted (in dollars per share)	0.00
Exercised (in dollars per share)	29.79
Forfeited (in dollars per share)	55.50
Weighted Average Exercise Prices, Outstanding, Ending Balance (in dollars per share)	$ 46.89	$ 46.18
Weighted Average Remaining Life in Years	1 year 5 months	2 years 4 months
Aggregate Intrinsic Value, Outstanding, Beginning Balance	$ 5
Aggregate Intrinsic Value, Outstanding, Ending Balance	$ 0	$ 5