Computation of Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	12 Months Ended
Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Computation of Earnings Per Share [Line Items]
Earnings available to common stockholders									$ 2,131	$ 2,263	$ 7,340
Basic weighted-average shares outstanding									302.7	329.9	376.1
Effect of convertible notes											0.3
Effect of employee stock awards									0.9	0.4	0.5
Diluted weighted-average shares outstanding									303.6	330.3	376.9
Earnings per share, basic	$ 1.99	$ 2.12	$ 2.67	$ 0.31	$ 1.26	$ 3.02	$ 1.78	$ 0.88	$ 7.04	$ 6.86	$ 19.52
Earnings per share, diluted	$ 1.99	$ 2.12	$ 2.66	$ 0.31	$ 1.26	$ 3.01	$ 1.78	$ 0.88	$ 7.02	$ 6.85	$ 19.47

Computation of Earnings Per Share [Line Items]

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- Definition

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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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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- Definition

Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

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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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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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