Common Stock - Stock Options Status and Activity (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended				12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares Under Option Outstanding Beginning Balance	759,327	940,965	1,125,527	1,144,719	1,144,719
Share Under Option, Canceled	(4,499)
Shares Under Option, Forfeited		(3,183)	(788)
Shares Under Option, Exercised	(148,303)	(178,455)	(183,774)	(19,192)
Shares Under Option Outstanding Ending Balance	606,525	759,327	940,965	1,125,527	606,525	1,144,719
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted Average Exercise Prices, Outstanding, Beginning Balance	$ 39.13	$ 37.46	$ 35.12	$ 34.69	$ 34.69
Weighted Average Exercise Price, Canceled	24.07
Weighted Average Exercise Prices, Forfeited		56.23	51.88
Weighted Average Exercise Prices, Exercised	42.01	30.17	23.07	9.31
Weighted Average Exercise Prices, Outstanding, Ending Balance	$ 38.54	$ 39.13	$ 37.46	$ 35.12	$ 38.54	$ 34.69
Weighted Average Remaining Life in Years	2 years 7 months 6 days	2 years 9 months 17 days	3 years 1 month 6 days	3 years 6 months		3 years 7 months 6 days
Aggregate Intrinsic Value, Outstanding, Beginning Balance	$ 12	$ 14	$ 12	$ 19	$ 19
Aggregate Intrinsic Value, Exercised		4	5	1	11	$ 10	$ 30
Aggregate Intrinsic Value, Outstanding, Ending Balance	$ 12	$ 12	$ 14	$ 12	$ 12	$ 19