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Income Taxes - Additional Information (Details) - USD ($) | 1 Months Ended | 3 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Income Tax Contingency [Line Items] |  |  |  |  |  |
Unamortized tax-deductible goodwill resulting from intercompany stock sales and reorganizations |  |  | $ 26,000,000 |  |  |
Unamortized tax-deduction rate on goodwill |  |  | 25.00% |  |  |
Tax cuts and jobs act of 2017, incomplete accounting, provisional income tax expense (benefit) | $ 272,000,000 | $ 272,000,000 | $ 59,000,000 |  |  |
Tax cuts and jobs act of 2017, incomplete accounting, provisional income tax expense (benefit), one-time transition tax |  |  | 16,000,000 |  |  |
Tax cuts and jobs act of 2017, incomplete accounting, provisional income tax expense (benefit), charge to record valuation allowance on U.S. foreign tax credits |  |  | $ 43,000,000 |  |  |
Percentage of temporary tax differences that reverse within the carryforward period |  |  | 24.00% |  |  |
Percentage of deferred tax asset exclusive of reversing temporary differences |  |  | 76.00% |  |  |
Deferred tax asset, increase (decrease), amount, foreign tax credit |  |  | $ 46,000,000 | $ 9,000,000 | $ 302,000,000 |
Deferred tax assets, tax credit carryforwards, foreign, expired during period |  |  | 8,000,000 | 57,000,000 | 128,000,000 |
Deferred tax assets, valuation allowance, foreign tax credit |  |  | 417,000,000 |  |  |
Valuation allowance, amount released | 98,000,000 | 98,000,000 | 10,000,000 | 98,000,000 |  |
Valuation allowance | 2,584,000,000 | 2,584,000,000 | 2,486,000,000 | 2,584,000,000 | 1,940,000,000 | $ 1,291,000,000
Increase (decrease) to valuation allowance |  |  | 136,000,000 | 831,000,000 | $ 772,000,000 |
Valuation allowance, changes due to losses no longer supported by temporary differences |  |  | 20,000,000 |  |  |
Net deferred tax assets other | (24,000,000) | (24,000,000) | $ (94,000,000) | $ (24,000,000) |  |
Percentage of the effect of unrecognized tax benefit, if recorded |  |  | 5.00% | 15.00% | 6.00% |
Interest or penalties recognized |  |  | $ 22,000,000 | $ 1,000,000 | $ 0 |
Income related to accrued interest and penalties |  |  | 1,000,000 | 2,000,000 | 0 |
Amount accrued for payment of interest and penalties | 2,000,000 | 2,000,000 | 21,000,000 | 2,000,000 |  |
Employee Service Share-based Compensation, Tax Benefit from Exercise of Stock Options |  |  |  |  | 0 |
Alcoa Corporation |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Deferred tax assets, tax credit carryforwards, foreign, expired during period |  |  |  | 302,000,000 |  |
Discrete income tax charge for valuation allowances |  |  |  | 1,267,000,000 |  |
Net deferred tax assets other |  |  |  |  | $ 2,000,000 |
Foreign Tax Authority |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Increase (decrease) to valuation allowance |  |  | 61,000,000 | 675,000,000 |  |
Internal Revenue Service IRS | Alcoa Corporation |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Net deferred tax assets | 925,000,000 | 925,000,000 |  | 925,000,000 |  |
Luxembourg |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Valuation allowance | 280,000,000 | 280,000,000 |  | 280,000,000 |  |
Luxembourg | Alcoa Corporation |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Net deferred tax assets | 42,000,000 | 42,000,000 |  | 42,000,000 |  |
Federal Tax Services of Russia |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Net deferred tax assets | 19,000,000 | 19,000,000 |  | 19,000,000 |  |
Canada Revenue Agency |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Net deferred tax assets | 20,000,000 | 20,000,000 |  | 20,000,000 |  |
Australia |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Valuation allowance | 93,000,000 | 93,000,000 |  | 93,000,000 |  |
Tax Authority, Spain |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Valuation allowance | $ 163,000,000 | $ 163,000,000 |  | $ 163,000,000 |  |
Tax Authority, Spain | Foreign Tax Authority |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Increase (decrease) to valuation allowance |  |  | 92,000,000 |  |  |
Other Net State Deferred Tax Asset |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Valuation allowance |  |  | $ 675,000,000 |  |  |

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