Stock-Based Compensation (Stock Based Compensation Activity) (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 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	$ 143
Number of Options, Balance	826		827
Options outstanding, intrinsic value	$ 20		$ 28
Stock Issued During Period, Value, Restricted Stock Award, Gross	$ 25	$ 23
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	3 years		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	25.88	$ 61.17
Weighted Average Grant Price, Vested/exercised	34.96
Weighted Average Grant Price, Canceled	45.92
Weighted Average Grant Price, Balance	$ 36.48		$ 43.34
Number of RSUs, Balance	819
Number of RSUs, Granted at fair market value	579
Number of RSUs, Vested/exercised	(375)
Number of RSUs, Canceled	(6)
Number of RSUs, Balance	1,017		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	23.74
Weighted Average Grant Price, Balance	$ 34.23		$ 35.18
Number of RSUs, Balance	941
Number of RSUs, Granted at fair market value	523
Number of RSUs, Vested/exercised	(486)
Number of RSUs, Canceled	(39)
Number of RSUs, Balance	939		941
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding	$ 26
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	1 year 8 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	$ 28
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 49