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Derivatives, Hedging Programs and Other Financial Instruments - Summary of Derivative Positions (Details) - 12 months ended Dec. 31, 2023 Mmlb in Millions | EUR (€) Mmlb MMBTU MW | GBP (£) Mmlb MMBTU MW
--- | --- | ---
Purchase | Aluminum |  |
Derivative [Line Items] |  |
Derivative non-monetary notional amount | 69.8 | 69.8
Purchase | Aluminum | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Jan. 31, 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 | 54.1 | 54.1
Purchase | Fixed Price Purchase Contracts for MWTP | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Jan. 31, 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 | 8.4 | 8.4
Purchase | Alloying Metals | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Jan. 31, 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 | 3,390,000 | 3,390,000
Purchase | Natural Gas | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Jan. 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 | MW | 52,704 | 52,704
Purchase | Electricity | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Jan. 31, 2024 |
Purchase | Electricity | Maximum |  |
Derivative [Line Items] |  |
Derivative maturity period | Dec. 31, 2024 |
Purchase | Euro |  |
Derivative [Line Items] |  |
Derivative notional amount | € | € 16,745,648 |
Purchase | Euro | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Jan. 31, 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 | 6.3 | 6.3
Sales | Aluminum | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Jan. 31, 2024 |
Sales | Aluminum | Maximum |  |
Derivative [Line Items] |  |
Derivative maturity period | Apr. 30, 2024 |
Sales | Fixed Price Sale Contracts for MWTP |  |
Derivative [Line Items] |  |
Derivative non-monetary notional amount | 26.6 | 26.6
Sales | Fixed Price Sale Contracts for MWTP | Minimum |  |
Derivative [Line Items] |  |
Derivative maturity period | Jan. 31, 2024 |
Sales | Fixed Price Sale Contracts for MWTP | Maximum |  |
Derivative [Line Items] |  |
Derivative maturity period | May 31, 2024 |

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