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Contingencies and Commitments - Additional Information - 2 (Detail) € in Millions, $ in Millions | 9 Months Ended |  |  |
--- | --- | --- | --- | ---
Sep. 30, 2017 USD ($) | Sep. 30, 2017 EUR (€) | Mar. 31, 2017 USD ($) | Dec. 31, 2016 USD ($)
Loss Contingencies [Line Items] |  |  |  |
Assessment for 2006 through 2009 tax years | $ 152 | € 129 |  |
Guarantees of third party related to project financing | 25 |  |  |
Letters of credit, total amount committed | $ 127 |  |  |
Letters of credit, expiration date | 2017 |  |  |
Total amount committed under outstanding surety bonds | $ 128 |  |  |
Surety bonds, expiration date | 2017 |  |  |
Other Noncurrent Liabilities and Deferred Credits [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Combined fair value of guarantees | $ 35 |  |  | $ 35
Separation Agreement [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Guarantees of third party related to project financing | 270 |  |  | 354
Total amount committed under outstanding surety bonds | 25 |  |  |
Supply Agreement [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Guarantees of third party related to project financing | 1,660 |  |  |
Purchase Agreement [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Guarantees of third party related to project financing |  |  |  | $ 245
Alcoa Corporation Energy Supply Contracts Guarantee [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Guarantees of third party related to project financing |  |  | $ 50 |
Alcoa Corporation Environmental Liabilities Guarantee [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Guarantees of third party related to project financing | 53 |  |  |
Alcoa Corporation Workers Compensation Claims [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Letters of credit, total amount committed | 61 |  |  |
Alcoa Corporation Equipment Leases And Energy Contracts [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Letters of credit, total amount committed | $ 103 |  |  |
Minimum [Member] | Separation Agreement [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Guarantees, expiration date | 2017 |  |  |
Minimum [Member] | Outstanding bank guarantees [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Guarantees, expiration date | 2017 |  |  |
Maximum [Member] | Separation Agreement [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Guarantees, expiration date | 2024 |  |  |
Maximum [Member] | Outstanding bank guarantees [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Guarantees, expiration date | 2026 |  |  |

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