| **Income Taxes (Details 3) (USD $)In Millions, unless otherwise specified** | Dec. 31, 2014                                  | Dec. 31, 2013                                  | Dec. 31, 2012                                  |
|-----------------------------------------------------------------------------|------------------------------------------------|------------------------------------------------|------------------------------------------------|
| **Deferred tax assets**                                                     |                                           |                                           |                                           |
| Deferred and refundable income taxes                                        | $ 94us-gaap_DeferredTaxAssetsNet               | $ 103us-gaap_DeferredTaxAssetsNet              | $ 104us-gaap_DeferredTaxAssetsNet              |
| **Deferred tax liabilities**                                                |                                           |                                           |                                           |
| Deferred income taxes and other liabilities                                 | (668)us-gaap_DeferredTaxLiabilities            | (500)us-gaap_DeferredTaxLiabilities            | (535)us-gaap_DeferredTaxLiabilities            |
| Deferred income taxes, net                                                  | $ (574)us-gaap_DeferredTaxAssetsLiabilitiesNet | $ (397)us-gaap_DeferredTaxAssetsLiabilitiesNet | $ (431)us-gaap_DeferredTaxAssetsLiabilitiesNet |

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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.
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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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