Computation of Earnings Per Share (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2012	Mar. 31, 2011
Net income available to common shareholders	$ 431	$ 225
Weighted average number of common shares	697,685	695,309
Basic earnings per share	$ 0.62	$ 0.32
Weighted average number of shares outstanding, diluted	707,369	704,101
Diluted earnings per share	$ 0.61	$ 0.32
Earnings Per Share, Basic [Member]
Net income available to common shareholders	431	225
Weighted average number of common shares	697,685	695,309
Basic earnings per share	$ 0.62	$ 0.32
Earnings Per Share, Diluted [Member]
Weighted average number of common shares	697,685	695,309
Net income available to common shareholders	$ 431	$ 225
Effect of dilutive outstanding equity-based awards	9,684	8,792
Weighted average number of shares outstanding, diluted	707,369	704,101
Diluted earnings per share	$ 0.61	$ 0.32

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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+ Details

- Definition

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.

+ References+ Details

- Definition

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.

+ References+ Details

- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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+ Details