Intrinsic and Fair Value of Stock-based Compensation (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value	[1]	$ 17	$ 28	$ 43
Share-based Compensation Arrangement by Share-based Payment Award, RSUs, Vested in Period, Fair Value	[1]	77	62	74
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value	[1]	$ 1	$ 0	$ 41

[1] Measured as of the grant date.