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Derivatives - Narrative (Details) - 6 months ended Jun. 30, 2023 € in Millions, kr in Millions	EUR (€) MMBTU MWh t	DKK (kr)
LME forward financial sales contracts
Derivative [Line Items]
Open position to offset fixed prices (in tonnes) \| t	59,187
Fixed For Floating Swaps
Derivative [Line Items]
Open position to offset fixed prices (in tonnes) \| t	2,961
FX Swaps
Derivative [Line Items]
Derivative asset \| €	€ 16.4
Nordpool Power Price Swap \| Grundartangi
Derivative [Line Items]
Derivative liability (in MwH) \| MWh	499,116
Indiana Hub Power Price Swaps
Derivative [Line Items]
Derivative liability (in MwH) \| MWh	88,320
USD ISK Forward Swap \| Not designated as hedging instrument \| Short
Derivative [Line Items]
Derivative, forward contracts \| kr		kr 24.0
USD Euro Forward Swap \| Not designated as hedging instrument \| Short
Derivative [Line Items]
Derivative, forward contracts \| €	€ 4.9
Henry Hub Natural Gas Price Swaps
Derivative [Line Items]
Derivative liability (in MwH) \| MMBTU	600,000