Stock-Based Compensation - Annual Activity Of Stock Options (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Number of Options, Balance at beginning of year	827
Number of Options - Granted	0
Number of Options - Exercised	(17)
Number of Options - Forfeited/expired	0
Number of Options, Balance at end of year	810	827
Weighted Average Exercise Price, Balance at beginning of year	$ 2.87
Weighted Average Exercise Price - Granted	0.00
Weighted Average Exercise Price - Exercised	0.79
Weighted Average Exercise Price - Forfeited/expired	0.00
Weighted Average Exercise Price, Balance at end of year	$ 2.91	$ 2.87
Aggregate Intrinsic Value - Beginning of Year	$ 28
Aggregate Intrinsic Value - Granted
Aggregate Intrinsic Value - Exercised	$ 1	$ 1	$ 6
Aggregate Intrinsic Value - End of Year	$ 27	$ 28
Weighted Average Remaining Contractual Term	2 years 3 months	3 years 3 months