Computation of Earnings Per Share (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Computation of Earnings Per Share
Net income available to common shareholders	$ 268	$ 469	$ 1,025	$ 1,410
Weighted average number of common shares	704,134	699,091	702,219	698,454
Effect of dilutive outstanding equity-based awards	11,967	10,784	11,063	9,985
Weighted average number of diluted common shares	716,101	709,875	713,282	708,439
Basic EPS	$ 0.38	$ 0.67	$ 1.46	$ 2.02
Diluted EPS	$ 0.37	$ 0.66	$ 1.44	$ 1.99
Anti-dilutive awards	22,570	24,676	30,141	33,380

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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+ Details

- 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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+ 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.

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+ Details