Earnings per Share - Computation of Basic and Diluted Earnings per Share (EPS) (Detail) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Basic EPS:
Net income	$ 932us-gaap_NetIncomeLoss	$ 480us-gaap_NetIncomeLoss
Weighted-average common shares outstanding	696,415	723,971
Basic EPS	$ 1.34us-gaap_EarningsPerShareBasic	$ 0.66us-gaap_EarningsPerShareBasic
Diluted EPS:
Net income	932us-gaap_NetIncomeLoss	480us-gaap_NetIncomeLoss
Change in fair value of conversion feature on 7.25% convertible senior notes	0	5
Net income for purposes of computing diluted EPS	$ 932	$ 485
Share computation for diluted earnings per share (in thousands):
Weighted-average shares outstanding	696,415	723,971
Dilutive effect of stock awards	20,515	13,534
Assumed conversion of convertible senior notes	0	3,830
Weighted average common shares outstanding	716,930	741,335
Diluted earnings per share	$ 1.30us-gaap_EarningsPerShareDiluted	$ 0.65us-gaap_EarningsPerShareDiluted
Stock options, SARs and RSUs because inclusion would be antidilutive	1	33

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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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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