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Contingencies and Commitments - Narrative (Detail) € in Millions, $ in Millions | 3 Months Ended |  |  |
--- | --- | --- | --- | ---
Mar. 31, 2018 USD ($) location | Mar. 31, 2018 EUR (€) | Dec. 31, 2017 USD ($) | Nov. 01, 2016 USD ($)
Loss Contingencies [Line Items] |  |  |  |
Number of cleanup locations | location | 100 |  |  |
Remediation reserve balance | $ 292 |  | $ 294 |
Remediation reserve balance, classified as a current liability | 40 |  | 41 |
Payments related to remediation expenses applied against the reserve | $ 3 |  |  |
Actual remediation fieldwork period | 4 years |  |  |
Assessment for 2006 through 2009 tax years | $ 161 | € 130 |  |
Guarantees of third party related to project financing | 27 |  |  |
Long-term debt | 6,312 |  | 6,807 |
Total amount committed under outstanding surety bonds | 55 |  |  |
Massena West, NY |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Remediation reserve balance | $ 213 |  | 215 |
Recurring Costs of Managing Hazardous Substances and Environmental Programs | Maximum |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Percentage of cost of goods sold | 1.00% |  |  |
Supply Agreement |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Guarantees of third party related to project financing | $ 1,188 |  | 1,297 |
Alcoa Corporation Workers Compensation Claims |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Letters of credit, total amount committed |  |  |  | $ 53
Other Noncurrent Liabilities and Deferred Credits |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Combined fair value of guarantees | 7 |  | 8 |
Separation Agreement |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Guarantees of third party related to project financing | 0 |  | $ 0 |
Total amount committed under outstanding surety bonds | 25 |  |  |
Bank Loan Obligations [Member] | Letter of Credit |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Long-term debt | $ 126 |  |  |

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