Earnings per Share (details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Earnings per Share disclosure
Net income	$ 833us-gaap_ProfitLoss	$ 1,052us-gaap_ProfitLoss
Participating share-based awards - allocated income	(6)	(7)
Net income available to common shareholders -- basic	827	1,045
Net income available to common shareholders -- diluted	$ 827	$ 1,045
Weighted average shares outstanding, basic	320.8	350.9
Weighted average effects of dilutive securities, stock options and performance shares (in shares)	3.7	3.7
Weighted average shares outstanding, diluted	324.5	354.6
Net income per common share, basic	$ 2.58us-gaap_EarningsPerShareBasic	$ 2.98us-gaap_EarningsPerShareBasic
Net income per common share, diluted	$ 2.55us-gaap_EarningsPerShareDiluted	$ 2.95us-gaap_EarningsPerShareDiluted

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 share based payment arrangements using the treasury stock 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 consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

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Amount of undistributed earnings (loss) allocated to participating securities for the basic earnings (loss) per share or per unit calculation under the two-class method.

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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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