| **Income Taxes (Details 3) (USD $)In Millions, unless otherwise specified** | Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010 |
|-----------------------------------------------------------------------------|---------------|---------------|---------------|
| **Deferred tax assets**                                                     |          |          |          |
| Deferred and refundable income taxes                                        | $ 104         | $ 84          | $ 85          |
| **Deferred tax liabilities**                                                |          |          |          |
| Deferred income taxes and other liabilities                                 | (539)         | (584)         | (594)         |
| Deferred income taxes, net                                                  | $ (435)       | $ (500)       | $ (509)       |

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| - Definition
Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards, net of deferred tax liability attributable to taxable temporary differences.
+ References
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| - Definition
Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.
+ References
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| - Definition
Amount of deferred tax liability attributable to taxable temporary differences net of deferred tax asset attributable to deductible temporary differences and carryforwards after valuation allowances.
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