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Income Taxes - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Other income tax disclosures |  |  |
Effect of unrecognized tax benefit on income tax expense | $ 41 | $ 37 | $ 38
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense | 2 | 3 |
Net accrued interest and penalties | 23 | $ 21 |
Maximum |  |  |
Other income tax disclosures |  |  |
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense |  |  | $ (1)
State |  |  |
Other income tax disclosures |  |  |
State NOL carryforwards | 2,056 |  |
Deferred income tax asset for State NOL carryforwards | 96 |  |
Federal |  |  |
Other income tax disclosures |  |  |
Federal NOL carryforward | 52 |  |
Deferred tax asset for Federal NOL carryforward | $ 11 |  |

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