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Contingencies, Commitments and Other Liabilities (Details) € in Millions, $ in Millions |  |  |  | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jun. 15, 2023 USD ($) | Mar. 31, 2023 USD ($) | Mar. 31, 2023 EUR (€) | Jan. 01, 2023 | Jul. 31, 2024 USD ($) | Dec. 31, 2023 USD ($) | Jul. 31, 2023 USD ($) | Sep. 30, 2024 USD ($) | Sep. 30, 2023 USD ($) | Sep. 30, 2024 USD ($) location | Sep. 30, 2023 USD ($) | Dec. 31, 2023 USD ($) | Dec. 31, 2023 EUR (€) | Jul. 23, 2024 USD ($) | Jul. 23, 2024 EUR (€) | Jun. 26, 2020 transaction entity
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of cleanup locations | location |  |  |  |  |  |  |  |  |  | 30 |  |  |  |  |  |
Remediation reserve balance |  |  |  |  |  | $ 17 |  | $ 19 |  | $ 19 |  | $ 17 |  |  |  |
Remediation reserve balance, classified as a current liability |  |  |  |  |  | 7 |  | 10 |  | 10 |  | 7 |  |  |  |
Payments related to remediation expenses applied against the reserve (less than in second quarter) |  |  |  |  |  |  |  | 1 |  | 2 |  |  |  |  |  |
Income tax reserve |  |  |  |  |  |  |  | 0 | $ 0 | 0 | $ 20 |  |  |  |  |
Guarantees of third party related to project financing |  |  |  |  |  |  |  | 23 |  | 23 |  |  |  |  |  |
Combined fair value of guarantees |  |  |  |  |  | 6 |  | 6 |  | 6 |  | $ 6 |  |  |  |
Coverage limit |  |  |  |  |  | $ 80 |  |  |  |  |  |  |  |  |  |
Total amount committed under outstanding surety bonds |  |  |  |  |  |  |  | 43 |  | 43 |  |  |  |  |  |
Surety bonds, amount outstanding |  |  |  |  |  |  |  | $ 21 |  | $ 21 |  |  |  |  |  |
Termination notice period (in days) |  |  |  | 30 days |  |  |  |  |  |  |  |  |  |  |  |
Payment timing (in days) |  |  |  | 120 days |  |  |  |  |  |  |  |  |  |  |  |
Supplier Finance Program, Obligation, Current, Statement of Financial Position [Extensible Enumeration] |  |  |  |  |  | Accounts payable, trade (Q) |  | Accounts payable, trade (Q) |  | Accounts payable, trade (Q) |  | Accounts payable, trade (Q) |  |  |  |
Supplier invoices subject to future payment |  |  |  |  |  | $ 258 |  | $ 251 |  | $ 251 |  | $ 258 |  |  |  |
Letter of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum borrowing capacity |  |  |  |  |  |  |  | 91 |  | 91 |  |  |  |  |  |
Other Noncurrent Liabilities and Deferred Credits | Separation Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantees of third party related to project financing |  |  |  |  |  | $ 1,131 |  | 1,131 |  | $ 1,131 |  | 1,131 |  |  |  |
Lehman Brothers International (Europe) (“LBIE”) Claims |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of entities | entity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2
Number of interest rate swap transactions | transaction |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2
Judgement from legal proceedings | $ 40 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments for legal settlements |  |  |  |  | $ 25 |  | $ 15 |  |  |  |  |  |  |  |  |
Foreign Tax Authority | Ministry of the Economy, Finance and Industry, France | Tax Years 2010 Through 2012 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income tax assessment, estimate of possible loss |  | $ 17 | € 16 |  |  |  |  |  |  |  |  |  |  |  |  |
Income tax assessment, amount of penalties cancelled |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 7 | € 7 |
Income tax reserve |  |  |  |  |  |  |  |  |  |  |  | $ 21 | € 19 |  |  |
Recurring Costs of Managing Hazardous Substances and Environmental Programs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of cost of goods sold (as a percent) |  |  |  |  |  |  |  |  |  | 1.00% |  |  |  |  |  |
Income Tax and Interest | Foreign Tax Authority | Ministry of the Economy, Finance and Industry, France | Tax Years 2010 Through 2012 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income tax assessment, estimate of possible loss |  | 10 | 9 |  |  |  |  |  |  |  |  |  |  |  |  |
Income Tax Penalties | Foreign Tax Authority | Ministry of the Economy, Finance and Industry, France | Tax Years 2010 Through 2012 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income tax assessment, estimate of possible loss |  | 7 | 7 |  |  |  |  |  |  |  |  |  |  |  |  |
Additional Interest on Income Tax | Foreign Tax Authority | Ministry of the Economy, Finance and Industry, France | Tax Years 2010 Through 2012 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income tax assessment, estimate of possible loss |  | $ 2 | € 2 |  |  |  |  |  |  |  |  |  |  |  |  |
Alcoa Corporation Workers Compensation Claims |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Letters of credit, total amount outstanding |  |  |  |  |  |  |  | 48 |  | $ 48 |  |  |  |  |  |
Arconic Corporation Environmental Obligations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Letters of credit, total amount outstanding |  |  |  |  |  |  |  | $ 17 |  | $ 17 |  |  |  |  |  |

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