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Derivatives, Hedging Programs and Other Financial Instruments - Summary of Derivative Positions (Details) - 9 months ended Sep. 30, 2024 Mmlb in Millions | EUR (€) MWh MMBTU Mmlb | GBP (£) MWh MMBTU Mmlb
--- | --- | ---
Purchase | Aluminum |  |
Derivative [Line Items] |  |
Derivative non-monetary notional amount | 61.2 | 61.2
Purchase | Aluminum | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Oct. 31, 2024 |
Purchase | Aluminum | Maximum |  |
Derivative [Line Items] |  |
Derivative maturity period | Feb. 28, 2026 |
Purchase | Fixed Price Purchase Contracts for MWTP |  |
Derivative [Line Items] |  |
Derivative non-monetary notional amount | 50.2 | 50.2
Purchase | Fixed Price Purchase Contracts for MWTP | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Oct. 31, 2024 |
Purchase | Fixed Price Purchase Contracts for MWTP | Maximum |  |
Derivative [Line Items] |  |
Derivative maturity period | Feb. 28, 2026 |
Purchase | Alloying Metals |  |
Derivative [Line Items] |  |
Derivative non-monetary notional amount | 9.7 | 9.7
Purchase | Alloying Metals | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Oct. 31, 2024 |
Purchase | Alloying Metals | Maximum |  |
Derivative [Line Items] |  |
Derivative maturity period | Dec. 31, 2026 |
Purchase | Natural Gas |  |
Derivative [Line Items] |  |
Derivative non-monetary notional amount | MMBTU | 3,080,000 | 3,080,000
Purchase | Natural Gas | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Oct. 31, 2024 |
Purchase | Natural Gas | Maximum |  |
Derivative [Line Items] |  |
Derivative maturity period | Dec. 31, 2026 |
Purchase | Electricity |  |
Derivative [Line Items] |  |
Derivative non-monetary notional amount | MWh | 55,225 | 55,225
Purchase | Electricity | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Oct. 31, 2024 |
Purchase | Electricity | Maximum |  |
Derivative [Line Items] |  |
Derivative maturity period | Dec. 31, 2024 |
Purchase | Euro |  |
Derivative [Line Items] |  |
Derivative notional amount | € | € 10,482,824 |
Purchase | Euro | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Oct. 31, 2024 |
Purchase | Euro | Maximum |  |
Derivative [Line Items] |  |
Derivative maturity period | Jul. 31, 2027 |
Purchase | British Pounds |  |
Derivative [Line Items] |  |
Derivative maturity period | Oct. 31, 2024 |
Derivative notional amount | £ |  | £ 72,266
Sales | Aluminum |  |
Derivative [Line Items] |  |
Derivative non-monetary notional amount | 9.4 | 9.4
Derivative maturity period | Oct. 31, 2024 |
Sales | Fixed Price Sale Contracts for MWTP |  |
Derivative [Line Items] |  |
Derivative non-monetary notional amount | 9.3 | 9.3
Derivative maturity period | Oct. 31, 2024 |
Sales | Electricity |  |
Derivative [Line Items] |  |
Derivative non-monetary notional amount | MWh | 28,717 | 28,717
Sales | Electricity | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Oct. 31, 2024 |
Sales | Electricity | Maximum |  |
Derivative [Line Items] |  |
Derivative maturity period | Dec. 31, 2024 |

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