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Derivatives, Hedging Programs and Other Financial Instruments - Summary of Derivative Positions (Details) - 3 months ended Mar. 31, 2024 Mmlb in Millions | EUR (€) Mmlb MWh MMBTU | GBP (£) Mmlb MWh MMBTU
--- | --- | ---
Purchase | Aluminum |  |
Derivative [Line Items] |  |
Derivative non-monetary notional amount | 74.5 | 74.5
Purchase | Aluminum | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Apr. 30, 2024 |
Purchase | Aluminum | Maximum |  |
Derivative [Line Items] |  |
Derivative maturity period | Dec. 31, 2025 |
Purchase | Fixed Price Purchase Contracts for MWTP |  |
Derivative [Line Items] |  |
Derivative non-monetary notional amount | 60.5 | 60.5
Purchase | Fixed Price Purchase Contracts for MWTP | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Apr. 30, 2024 |
Purchase | Fixed Price Purchase Contracts for MWTP | Maximum |  |
Derivative [Line Items] |  |
Derivative maturity period | Dec. 31, 2025 |
Purchase | Alloying Metals |  |
Derivative [Line Items] |  |
Derivative non-monetary notional amount | 10.0 | 10.0
Purchase | Alloying Metals | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Apr. 30, 2024 |
Purchase | Alloying Metals | Maximum |  |
Derivative [Line Items] |  |
Derivative maturity period | Dec. 31, 2025 |
Purchase | Natural Gas |  |
Derivative [Line Items] |  |
Derivative non-monetary notional amount | MMBTU | 3,880,000 | 3,880,000
Purchase | Natural Gas | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Apr. 30, 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 | 39,606 | 39,606
Purchase | Electricity | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Apr. 30, 2024 |
Purchase | Electricity | Maximum |  |
Derivative [Line Items] |  |
Derivative maturity period | Dec. 31, 2024 |
Purchase | Euro |  |
Derivative [Line Items] |  |
Derivative notional amount | € | € 17,485,138 |
Purchase | Euro | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Apr. 30, 2024 |
Purchase | Euro | Maximum |  |
Derivative [Line Items] |  |
Derivative maturity period | Jan. 31, 2026 |
Purchase | British Pounds |  |
Derivative [Line Items] |  |
Derivative notional amount | £ |  | £ 216,799
Purchase | British Pounds | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | May 31, 2024 |
Purchase | British Pounds | Maximum |  |
Derivative [Line Items] |  |
Derivative maturity period | Jul. 31, 2024 |
Sales | Aluminum |  |
Derivative [Line Items] |  |
Derivative non-monetary notional amount | 7.0 | 7.0
Derivative maturity period | Apr. 30, 2024 |
Sales | Fixed Price Sale Contracts for MWTP |  |
Derivative [Line Items] |  |
Derivative non-monetary notional amount | 26.7 | 26.7
Sales | Fixed Price Sale Contracts for MWTP | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Apr. 30, 2024 |
Sales | Fixed Price Sale Contracts for MWTP | Maximum |  |
Derivative [Line Items] |  |
Derivative maturity period | Sep. 30, 2024 |

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