Stock-Based Compensation (Stock Based Compensation Activity) (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Document Period End Date	Jun. 30, 2017
Number of Options, Balance	801		810
Options outstanding, intrinsic value	$ 19		$ 27
Stock Issued During Period, Value, Restricted Stock Award, Gross	$ 22	$ 25
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	1 year 9 months		2 years 3 months
Performance-Based and Market-Based RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Average Grant Price, Balance	$ 34.11
Weighted Average Grant Price, Granted at fair market value	34.41	$ 23.29
Weighted Average Grant Price, Vested/exercised	36.55
Weighted Average Grant Price, Canceled	39.51
Weighted Average Grant Price, Balance	$ 32.55		$ 34.11
Number of RSUs, Balance	923
Number of RSUs, Granted at fair market value	572
Number of RSUs, Vested/exercised	(146)
Number of RSUs, Canceled	(276)
Number of RSUs, Balance	1,073		923
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding	$ 29
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	1 year 6 months
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Average Grant Price, Balance	$ 34.83
Weighted Average Grant Price, Granted at fair market value	34.41	$ 25.86
Weighted Average Grant Price, Vested/exercised	36.69
Weighted Average Grant Price, Canceled	32.49
Weighted Average Grant Price, Balance	$ 33.80		$ 34.83
Number of RSUs, Balance	878
Number of RSUs, Granted at fair market value	528
Number of RSUs, Vested/exercised	(447)
Number of RSUs, Canceled	(50)
Number of RSUs, Balance	909		878
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding	$ 25
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 45