Earnings per share (Details) (USD $) In Millions, except Per Share data	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Income (Numerator):
Net income for basic and diluted Earnings Per Share	$ 1,170	$ 1,202	$ 2,295	$ 2,369
Shares (Denominator):
Weighted-average shares for basic Earnings Per Share	927	959	930	970
Effect of dilutive securities	8	5	8	6
Weighted-average shares for diluted Earnings Per Share	935	964	938	976
Basic Earnings Per Share	$ 1.26	$ 1.25	$ 2.47	$ 2.44
Diluted Earnings Per Share	$ 1.25	$ 1.25	$ 2.45	$ 2.43

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 portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

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-Appendix A

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Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Glossary Other Comprehensive Income
-URI http://asc.fasb.org/extlink&oid=6519514

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Reference 12: http://www.xbrl.org/2003/role/presentationRef
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-Glossary Net Income
-URI http://asc.fasb.org/extlink&oid=6518256

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+ Details

- Definition

The sum of dilutive potential common shares or units used in the calculation of the diluted per-share or per-unit computation.

+ 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

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Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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+ Details