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Commitments and Contingencies (Details)
1 Months Ended 6 Months Ended 12 Months Ended
Aug. 18, 2017
USD ($)
Oct. 31, 2021
USD ($)
Sep. 30, 2017
USD ($)
Jun. 30, 2024
USD ($)
laborUnion
MW
Dec. 31, 2013
USD ($)
Jun. 30, 2023
USD ($)
Labor Commitments [Abstract]            
Percentage of total work force in union       59.00%    
Percentage of Grundartangi work force represented by the labor unions       87.00%    
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       38.00%    
Percentage of foreign work force, represented by the union       61.00%    
Contingent consideration, accrued interest and principal       $ 31,600,000    
Netherlands            
Labor Commitments [Abstract]            
Percentage of total work force in union       100.00%    
PBGC            
PBGC Settlement [Abstract]            
Required pension contributions above minimum         $ 17,400,000  
Pension contributions, amended term, annual contribution   $ 2,400,000        
Pension contributions, amended term, total contribution   $ 9,600,000   $ 6,900,000   $ 2,400,000
Pension contributions, term   4 years        
Payment for pension benefits       $ 0    
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 and OR            
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    
Power currently available under the power purchase agreement, requested (in megawatts) | MW       182    
Ravenswood Retiree Medical Benefits Changes            
Ravenswood litigation [Abstract]            
Litigation settlement amount $ 23,000,000.0          
Ravenswood litigation settlement installment period 10 years          
Litigation payment to trust     $ 5,000,000.0      
Gain (loss) related to litigation settlement     5,500,000      
Loss contingency accrual     $ 12,500,000      
Litigation settlement, annual installment       $ 2,000,000.0    
Litigation settlement installment period       9 years    
Other current liabilities       $ 2,000,000.0    
Other Liabilities       $ 3,500,000