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Derivatives - Narrative (Details) - 3 months ended Mar. 31, 2023 € in Millions, $ in Millions	USD ($) MWh t	EUR (€)
LME Swap
Derivative [Line Items]
Open position to offset fixed prices (in tonnes) \| t	70,464
Fixed For Floating Swaps
Derivative [Line Items]
Open position to offset fixed prices (in tonnes) \| t	2,878
Nordpool Power Price Swap \| Grundartangi
Derivative [Line Items]
Derivative liability (in MwH) \| MWh	745,908
FX Swap
Derivative [Line Items]
Derivative asset \| €		€ 24.5
Indiana Hub Power Price Swaps
Derivative [Line Items]
Derivative liability (in MwH) \| MWh	132,000
USD ISK Forward Swap \| Not designated as hedging instrument \| Short
Derivative [Line Items]
Derivative, forward contracts \| $	$ 4,346.7
USD Euro Forward Swap \| Not designated as hedging instrument \| Long
Derivative [Line Items]
Derivative, forward contracts \| $	$ 7.6