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Income Taxes (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
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Sep. 30, 2018 | Jun. 30, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Income Tax Disclosure [Abstract] |  |  |  |  |  |
Effective income tax rate | 20.10% |  |  | 2.00% | 1.10% | (49.80%)
Provisional income tax expense |  |  | $ 345 |  |  |
Reduction in provisional expense for remeasurement of deferred taxes |  | $ 11 |  |  |  |
Increase in provisional expense for transition tax | $ 24 |  |  |  |  |
Effect of change to provisional transition tax (percentage) | 12.40% |  |  |  | 2.90% |

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