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Hawesville

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Insurance Contingencies

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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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Number Of Potlines

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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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Percentage Of Foreign Work Force, Represented By Union

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

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Power Supply Agreement, Extension Term

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Ravenswood litigation [Abstract]

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Short-term Power Agreement, Supply Percentage

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Temporary Reduction In Production, 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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Commitments and Contingencies (Details) $ in Millions		1 Months Ended	6 Months Ended
Commitments and Contingencies (Details) $ in Millions	Aug. 18, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2026 USD ($) laborUnion qtr MW	Feb. 13, 2026 USD ($)	Oct. 31, 2025	Nov. 30, 2024 potline
Hawesville [Abstract]
Partial withdrawal liability			$ 5.1	$ 5.7
Insurance Contingencies [Abstract]
Number of potlines effected by transformer \| potline						1
Number of potlines \| potline						2
Reduction in production percentage					66.67%
Labor Commitments [Abstract]
Percentage of total work force in union			57.00%
Percentage of Grundartangi work force represented by the labor unions			89.00%
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			35.00%
Percentage of foreign work force, represented by the union			63.00%
Contingent consideration, accrued interest and principal			$ 21.5
Location, Statement of Financial Position, Balance [Axis]: us-gaap:AccruedEmployeeBenefitsCurrent
Hawesville [Abstract]
Partial withdrawal liability			2.3
Location, Statement of Financial Position, Balance [Axis]: us-gaap:DefinedBenefitPensionPlanLiabilitiesNoncurrent
Hawesville [Abstract]
Partial withdrawal liability			2.8
First 9 Quarters
Hawesville [Abstract]
Quarterly cost			$ 0.6
Number of quarters \| qtr			8
Final Quarter
Hawesville [Abstract]
Quarterly cost			$ 0.5
Number of quarters \| qtr			1
E ON Contingent Obligation \| Long-Term Debt
Labor Commitments [Abstract]
Stated interest rate, percentage			11.00%
Netherlands
Labor Commitments [Abstract]
Percentage of total work force in union			100.00%
Kenergy \| Century Marketer, LLC
Power Commitments and Contingencies [Abstract]
Extension term			1 year
Required termination period			1 year
Sebree \| Kenergy
Power Commitments and Contingencies [Abstract]
Extension term			1 year
Required termination period			1 year
Santee Cooper
Power Commitments and Contingencies [Abstract]
Power agreement, power supply, percentage			100.00%
Grundartangi - HS, Landsvirkjun and OR
Power Commitments and Contingencies [Abstract]
Power currently available under the power purchase agreement, available (in megawatts) \| MW			545
Grundartangi - Landsvirkjun
Power Commitments and 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