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Income taxes (Details) (USD $)
In Millions, unless otherwise specified |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
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Sep. 30, 2012
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Sep. 30, 2011
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Sep. 30, 2012
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Sep. 30, 2011
|
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| Puerto Rico Excise Tax Rate [Line Items] | ||||
| Effective tax rate for the period excluding the impact of the tax credits associated with the new Pr excise tax and legal settlement charge | 17.70% | 13.90% | 18.30% | 17.10% |
| Income taxes (Textual) [Abstract] | ||||
| Increase in gross amount of unrecognized tax benefits for period | $ 99 | $ 249 | ||
| Decrease in unrecognized tax benefits that is reasonably possible within the succeeding 12 months due to resolution of federal and state audits | $ 330 | $ 330 | ||
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Puerto Rico Excise Tax [Member]
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| Puerto Rico Excise Tax Rate [Line Items] | ||||
| Period that excise tax is imposed | 6 years | |||
| Effective excise tax rate for 2011 | 4.00% | |||
| Effective excise tax rate for 2012 | 3.75% | |||
| Effective excise tax rate for 2013 | 2.75% | |||
| Effective excise tax rate for 2014 | 2.50% | |||
| Effective excise tax rate for 2015 | 2.25% | |||
| Effective excise tax rate for 2016 | 1.00% | |||