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Contingencies and Commitments (Details) € in Millions, $ in Millions | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Mar. 31, 2019 USD ($) | Mar. 31, 2019 EUR (€) | Dec. 31, 2018 USD ($) location | Mar. 31, 2019 EUR (€) | Nov. 01, 2016 USD ($)
Loss Contingencies [Line Items] |  |  |  |  |
Number of cleanup locations | location |  |  | 100 |  |
Remediation reserve balance | $ 261 |  | $ 266 |  |
Remediation reserve balance, classified as a current liability | 79 |  | 81 |  |
Payments related to remediation expenses applied against the reserve | 3 |  |  |  |
Income tax examination assessment outstanding | 171 |  |  | € 152 |
Guarantees of third party related to project financing | 29 |  |  |  |
Total amount committed under outstanding surety bonds | 50 |  |  |  |
Bank Loan Obligations |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Letters of credit, total amount | 136 |  |  |  |
Separation Agreement |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Total amount committed under outstanding surety bonds | 25 |  |  |  |
Other Noncurrent Liabilities and Deferred Credits |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Combined fair value of guarantees | 7 |  | 6 |  |
Other Noncurrent Liabilities and Deferred Credits | Separation Agreement |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Guarantees of third party related to project financing | 1,143 |  | 1,087 |  |
Massena West, NY |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Remediation reserve balance | 195 |  | $ 198 |  |
Spain |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Established tax reserve | 59 | € 52 |  |  |
Tax indemnification receivable | $ 28 |  |  | € 25 |
Alcoa Corporation |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Tax agreement, indemnification of ultimate liability, percent | 49.00% |  |  | 49.00% |
Recurring Costs of Managing Hazardous Substances and Environmental Programs | Maximum |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Percentage of cost of goods sold | 1.00% | 1.00% |  |  |
Alcoa Corporation Workers Compensation Claims |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Letters of credit, total amount outstanding |  |  |  |  | $ 54

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