Computation of Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
Mar. 31, 2016	Mar. 31, 2015
Basic earnings per share:
Earnings available to common stockholders	$ 313	$ 508
Basic weighted-average shares outstanding	354	382
Earnings per share, basic	$ 0.88	$ 1.33
Diluted earnings per share:
Earnings available to common stockholders including the effect of dilutive securities	$ 313	$ 508
Diluted shares outstanding:
Basic weighted-average shares outstanding	354	382
Effect of convertible notes		1
Effect of employee stock awards	1	1
Diluted weighted-average shares outstanding	355	384
Earnings per share, diluted	$ 0.88	$ 1.32

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of convertible debt securities using the if-converted method.

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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Net Income or Loss Available to Common Stockholders plus adjustments resulting from the assumption that dilutive convertible securities were converted, options or warrants were exercised, or that other shares were issued upon the satisfaction of certain conditions.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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