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Derivatives - Narrative (Details) € in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($) MWh t	Mar. 31, 2022 EUR (€)	Dec. 31, 2021 USD ($)
Derivative [Line Items]
Restricted cash \| $	$ 18.5		$ 8.6
LME Swap [Member]
Derivative [Line Items]
Open position to offset fixed prices (in tonnes)	118,341
Midwest Premium (MWP) [Member]
Derivative [Line Items]
Open position to offset fixed prices (in tonnes)	152,250
Fixed For Floating Swaps [Member]
Derivative [Line Items]
Open position to offset fixed prices (in tonnes)	4,816
Nordpool Power Price Swap [Member] \| Grundartangi [Member]
Derivative [Line Items]
Derivative liability (in MwH) \| MWh	1,755,100
FX Swap [Member]
Derivative [Line Items]
Derivative asset \| €		€ 48.3
Indiana Hub Power Price Swaps [Member]
Derivative [Line Items]
Derivative liability (in MwH) \| MWh	307,200