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Income Taxes - Additional Information (Detail) - USD ($) |  | 3 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Jul. 12, 2014 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Tax benefit (charge) realized from exercise of employee stock options |  |  |  | $ (1,000,000) | $ 0 | $ 2,000,000 |
Unamortized tax-deductible goodwill resulting from intercompany stock sales and reorganizations |  |  |  | $ 24,000,000 |  |  |
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 |  |  |  |  |
Percentage of temporary tax differences that reverse within the carryforward period |  |  |  |  | 30.00% |  |
Percentage of deferred tax asset exclusive of reversing temporary differences |  |  |  |  | 70.00% |  |
Increase (decrease) to valuation allowance |  |  | $ 1,267,000,000 | $ 831,000,000 | $ 772,000,000 | 180,000,000 |
Valuation allowance |  | 2,584,000,000 | 1,940,000,000 | 2,584,000,000 | 1,940,000,000 | $ 1,291,000,000 | $ 1,151,000,000
Tax credit carryforward, valuation allowance |  | 379,000,000 |  | 379,000,000 |  |  |
Net deferred tax assets other |  | (24,000,000) | (164,000,000) | $ (24,000,000) | $ (164,000,000) |  |
Percentage of tax rate decreased |  |  |  | 52.50% | (15.70%) | (1.00%) |
Percentage of the effect of unrecognized tax benefit, if recorded |  |  |  | 15.00% | 6.00% | 7.00% |
Interest or penalties recognized |  |  |  | $ 1,000,000 | $ 0 | $ 0 |
Income related to accrued interest and penalties |  |  |  | 2,000,000 | 0 | 1,000,000 |
Amount accrued for payment of interest and penalties |  | 2,000,000 | 2,000,000 | 2,000,000 | 2,000,000 |  |
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) |  | (2,000,000) |  |
State and Local Jurisdiction |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Increase (decrease) to valuation allowance |  |  |  | 98,000,000 |  |  |
Valuation allowance |  | 750,000,000 |  | 750,000,000 |  |  |
Foreign Tax Authority |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Foreign tax credits carry forward period | 10 years |  |  |  |  |  |
Tax credit carryforward, valuation allowance |  | 302,000,000 |  | 302,000,000 |  | 134,000,000 |
Deferred tax assets, tax credit carryforwards, foreign, expired during period |  |  |  | 57,000,000 | 128,000,000 | 15,000,000 |
Iceland And Suriname |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Discrete income tax charge for valuation allowances |  |  |  |  |  | 141,000,000 |
Suriname |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Valuation allowance |  |  |  |  |  | $ 85,000,000 |
Suriname | Minimum |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Foreign tax credits expiry period |  |  |  |  |  | 2016 |
Suriname | Maximum |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Foreign tax credits expiry period |  |  |  |  |  | 2022 |
Iceland |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Valuation allowance |  |  |  |  |  | $ 56,000,000 |
Iceland | Minimum |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Foreign tax credits expiry period |  |  |  |  |  | 2017 |
Iceland | Maximum |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Foreign tax credits expiry period |  |  |  |  |  | 2023 |
Internal Revenue Service IRS | Alcoa Corporation |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Net deferred tax assets |  |  | 925,000,000 |  | 925,000,000 |  |
Luxembourg |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Valuation allowance |  |  | 280,000,000 |  | 280,000,000 |  |
Discrete income tax charge for valuation allowances |  |  |  |  | 42,000,000 |  |
Luxembourg | Alcoa Corporation |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Net deferred tax assets |  |  | 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 |  |
Canada Revenue Agency |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Net deferred tax assets |  |  | 20,000,000 |  | 20,000,000 |  |
Australia |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Valuation allowance |  |  | 93,000,000 |  | 93,000,000 |  |
Tax Authority, Spain |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Valuation allowance |  |  | $ 163,000,000 |  | $ 163,000,000 |  |
Tax Authority, Spain | Foreign Tax Authority |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Increase (decrease) to valuation allowance |  |  |  | 675,000,000 |  |  |
Excess Foreign Tax Credits |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Tax credit carryforward, valuation allowance |  | 23,000,000 |  | 23,000,000 |  |  |
Tax Credits, Other Adjustments |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Tax credit carryforward, valuation allowance |  | $ (14,000,000) |  | $ (14,000,000) |  |  |

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