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Income Taxes - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Income Tax [Line Items] |  |  |
Income tax benefit, adjustment | $ 4 |  |
Other income tax disclosures |  |  |
Effect of unrecognized tax benefit on income tax expense | 38 | $ 38 | $ 29
Interest and penalties expense related to unrecognized income tax expense (benefit) |  | 3 | $ (2)
Net accrued interest and penalties | 19 | $ 19 |
Maximum |  |  |
Other income tax disclosures |  |  |
Interest and penalties expense related to unrecognized income tax expense (benefit) | (1) |  |
State |  |  |
Other income tax disclosures |  |  |
State NOL carryforwards | 1,911 |  |
Deferred tax asset for State NOL carryforwards | 84 |  |
Federal |  |  |
Other income tax disclosures |  |  |
Deferred tax asset for Federal NOL carryforward | $ 12 |  |

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