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Litigation Settlement Payment Period

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The number of labor unions representing a group of employees.

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Pension Contributions, Term

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The percentage of a Company's work force, based in the country of domicile, that are subject to collective bargaining agreements.

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The percentage of a Company's Icelandic work force that are subject to collective bargaining agreements.

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The percentage of a Company's work force that are subject to collective bargaining agreements.

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Ravenswood litigation

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Short-term Power Agreement, Supply Percentage

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The power currently available under the power purchase agreement.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount of gain (loss) recognized in settlement of litigation and insurance claims. Excludes claims within an insurance entity's normal claims settlement process.

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Amount awarded to other party in judgment or settlement of litigation.

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Amount of loss contingency liability.

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Commitments and Contingencies (Details) $ in Millions			1 Months Ended	12 Months Ended
Commitments and Contingencies (Details) $ in Millions	Oct. 01, 2021 USD ($)	Aug. 18, 2017 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2024 USD ($) laborUnion MW	Dec. 31, 2013 USD ($)
Labor Commitments [Abstract]
Percentage of total work force in union				59.00%
Percentage of Grundartangi work force represented by the labor unions				86.00%
Number of labor unions Grundartangi subsidiary entered into a new labor agreement with \| laborUnion				5
Percentage of domestic based work force represented by a union				39.00%
Percentage of foreign work force represented by union				0.61
Contingent consideration, accrued interest and principal				$ 32.3
E.ON Contingent Obligation \| Long-term Debt
Labor Commitments [Abstract]
Stated interest rate, percentage				10.94%
Netherlands
Labor Commitments [Abstract]
Percentage of total work force in union				100.00%
Pension Benefit Guarantee Corporation
PBGC Settlement [Abstract]
Required pension contributions above minimum					$ 17.4
Pension contributions, amended term, annual contribution	$ 2.4
Pension contributions, amended term, total contribution	$ 9.6			$ 7.2
Pension contributions, term	4 years
Kenergy \| Century Marketer, LLC
Power Contingencies [Abstract]
Extension term				1 year
Required termination period				1 year
Hawesville \| Kenergy
Power Contingencies [Abstract]
Extension term				1 year
Required termination period				1 year
Sebree \| Kenergy
Power Contingencies [Abstract]
Extension term				1 year
Required termination period				1 year
Santee Cooper
Power Contingencies [Abstract]
Power agreement, power supply, percentage				100.00%
Grundartangi - HS, Landsvirkjun
Power Contingencies [Abstract]
Power currently available under the power purchase agreement, available (in megawatts) \| MW				545
Grundartangi - Landsvirkjun
Power Contingencies [Abstract]
Power currently available under the power purchase agreement, available (in megawatts) \| MW				25
Ravenswood Retiree Medical Benefits Changes
Ravenswood litigation [Abstract]
Litigation settlement amount		$ 23.0
Ravenswood litigation settlement installment period		10 years
Litigation payment to trust			$ 5.0
Gain (loss) related to litigation settlement			5.5
Loss contingency accrual			$ 12.5
Litigation settlement, annual installment				$ 2.0
Litigation settlement installment period				9 years
Other current liabilities				$ 2.0
Other liabilities				$ 1.6