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, 2016	Jun. 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	$ 106
Number of Options, Balance	821		827
Options outstanding, intrinsic value	$ 24		$ 28
Stock Issued During Period, Value, Restricted Stock Award, Gross	$ 25	$ 24
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	2 years 9 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	25.86	$ 61.17
Weighted Average Grant Price, Vested/exercised	34.93
Weighted Average Grant Price, Canceled	39.02
Weighted Average Grant Price, Balance	$ 36.45		$ 43.34
Number of RSUs, Balance	819
Number of RSUs, Granted at fair market value	584
Number of RSUs, Vested/exercised	(377)
Number of RSUs, Canceled	(13)
Number of RSUs, Balance	1,013		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	23.29	$ 55.51
Weighted Average Grant Price, Vested/exercised	25.12
Weighted Average Grant Price, Canceled	24.04
Weighted Average Grant Price, Balance	$ 34.20		$ 35.18
Number of RSUs, Balance	941
Number of RSUs, Granted at fair market value	526
Number of RSUs, Vested/exercised	(486)
Number of RSUs, Canceled	(41)
Number of RSUs, Balance	940		941
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding	$ 30
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	1 year 6 months
Cash Unit Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
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	$ 41