Stock-Based Compensation (Stock Based Compensation Activity) (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation	$ 96
Number of Options, Balance	814		827
Options outstanding, intrinsic value	$ 25		$ 28
Stock Issued During Period, Value, Restricted Stock Award, Gross	$ 27	$ 24
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	2 years 6 months		3 years 3 months
Time-Based RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Average Grant Price, Balance	$ 43.34
Weighted Average Grant Price, Granted at fair market value	25.92	$ 54.72
Weighted Average Grant Price, Vested/exercised	36.06
Weighted Average Grant Price, Canceled	38.34
Weighted Average Grant Price, Balance	$ 36.01		$ 43.34
Number of RSUs, Balance	819
Number of RSUs, Granted at fair market value	587
Number of RSUs, Vested/exercised	(422)
Number of RSUs, Canceled	(25)
Number of RSUs, Balance	959		819
Performance-Based and Market-Based RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Average Grant Price, Balance	$ 35.18
Weighted Average Grant Price, Granted at fair market value	23.33	$ 55.51
Weighted Average Grant Price, Vested/exercised	25.13
Weighted Average Grant Price, Canceled	27.16
Weighted Average Grant Price, Balance	$ 34.14		$ 35.18
Number of RSUs, Balance	941
Number of RSUs, Granted at fair market value	528
Number of RSUs, Vested/exercised	(488)
Number of RSUs, Canceled	(51)
Number of RSUs, Balance	930		941
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding	$ 32
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	1 year 3 months
Cash Unit Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value	$ 2	$ 2
Weighted Average Grant Price, Balance	$ 18.04
Weighted Average Grant Price, Granted at fair market value	0.00
Weighted Average Grant Price, Vested/exercised	18.04
Weighted Average Grant Price, Canceled	0.00
Weighted Average Grant Price, Balance	$ 0.00		$ 18.04
Number of RSUs, Balance	111
Number of RSUs, Granted at fair market value	0
Number of RSUs, Vested/exercised	(111)
Number of RSUs, Canceled	0
Number of RSUs, Balance	0		111
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding	$ 33
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 34