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Contingencies and Commitments - Commitments (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2024
Loss Contingencies [Line Items] |  |  |  |
Purchase obligations due in 2025 | $ 237 |  |  | $ 237
Purchase obligations due in 2026 | 51 |  |  | 51
Purchase obligations due in 2027 | 42 |  |  | 42
Purchase obligations due in 2028 | 40 |  |  | 40
Purchase obligations due in 2029 | 39 |  |  | 39
Purchase obligations due thereafter | 0 |  |  | $ 0
Indemnification of liability (as a percent) |  |  |  | 50.00%
Guarantees of third party related to project financing | 6 |  |  | $ 6
Combined fair value of guarantees | 6 | $ 6 |  | 6
Insurance annual coverage limit | 80 | 80 | $ 80 |
Total amount committed under outstanding surety bonds | 44 |  |  | 44
Amount of outstanding surety bonds relating to these liabilities | 21 |  |  | 21
Alcoa Corporation Workers Compensation Claims |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Letters of credit, total amount committed | 48 |  |  | 48
Arconic Corporation Environmental Obligations |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Letters of credit, total amount committed | 17 |  |  | 17
Letter of Credit |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Maximum borrowing capacity | 90 |  |  | 90
Other Noncurrent Liabilities and Deferred Credits | Separation Agreement |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Guarantees of third party related to project financing | $ 1,121 | $ 1,131 |  | $ 1,121

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