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Derivatives - Narrative (Details) € in Millions, kr in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2023 DKK (kr) MMBTU MWh Boe t | Dec. 31, 2023 EUR (€) | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($)
Supply Commitment [Line Items] |  |  |  |
Restricted cash | $ |  |  | $ 0 | $ 0
LME forward financial sales contracts |  |  |  |
Supply Commitment [Line Items] |  |  |  |
Open position to offset fixed prices | t | 36,633 |  |  |
Fixed to Floating Swap |  |  |  |
Supply Commitment [Line Items] |  |  |  |
Open position to offset fixed prices | t | 318 |  |  |
Nord Pool Swaps | Nordural Grundartangi ehf |  |  |  |
Supply Commitment [Line Items] |  |  |  |
Derivative liability (in MwH) | MWh | 0 |  |  |
Indiana Hub Power Price Swaps |  |  |  |
Supply Commitment [Line Items] |  |  |  |
Derivative liability (in MwH) | MWh | 0 |  |  |
USD ISK Forward Swap | Not Designated as Hedging Instrument | Short |  |  |  |
Supply Commitment [Line Items] |  |  |  |
Derivative, forward contracts | kr | kr 397.0 |  |  |
USD Euro Forward Swap | Not Designated as Hedging Instrument | Short |  |  |  |
Supply Commitment [Line Items] |  |  |  |
Derivative, forward contracts | € |  | € 1.8 |  |
Henry Hub Natural Gas Price Swaps |  |  |  |
Supply Commitment [Line Items] |  |  |  |
Derivative liability (in MwH) | MMBTU | 0 |  |  |
HFO Price Swaps |  |  |  |
Supply Commitment [Line Items] |  |  |  |
Derivative liability (in MwH) | Boe | 180,000 |  |  |

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