v3.26.1
Business Segments - Reconciliation of Net Income (Loss) (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Segment Reporting [Line Items]        
Net sales $ 752.1 $ 628.1 $ 1,401.3 $ 1,262.0
Selling, general and administrative expenses (15.9) (14.0) (41.7) (26.5)
Gain on the sale of Hawesville 0.0 0.0 287.9 0.0
Other operating expense - net (0.4) (1.5) (7.3) (3.5)
Interest income 4.4 1.9 7.5 3.7
Gain on insurance proceeds - net 40.1 0.0 73.1 0.0
Other income (loss) - net 3.8 (5.7) (1.7) (9.1)
Income tax (expense) benefit (12.1) 1.3 (13.9) (0.3)
Equity in losses of unconsolidated subsidiaries (1.0) 0.0 (1.0) 0.0
Net income (loss) 243.8 (11.7) 570.8 10.7
Nonrelated Party        
Segment Reporting [Line Items]        
Net sales 421.2 260.5 764.5 515.7
Interest expense (9.5) (9.8) (19.4) (19.8)
Net gain (loss) on forward and derivative contracts - nonaffiliates 7.1 (15.6) (58.2) (21.0)
Related Party        
Segment Reporting [Line Items]        
Net sales 330.9 367.6 636.8 746.3
Interest expense (0.6) (1.9) (1.2) (3.7)
Reportable Segment        
Segment Reporting [Line Items]        
Net sales 752.1 628.1 1,401.3 1,262.0
Segment Cost of goods sold (532.9) (593.2) (1,070.1) (1,165.6)
IRA Section 45X tax credit 26.3 21.9 51.3 41.8
Lower of cost or NRV inventory adjustment (4.3) 1.2 (1.0) 1.9
Property and equipment expense (13.3) (24.4) (34.8) (49.2)
Selling, general and administrative expenses (15.9) (14.0) (41.7) (26.5)
Gain on the sale of Hawesville 0.0 0.0 287.9 0.0
Other operating expense - net (0.4) (1.5) (7.3) (3.5)
Interest income 4.4 1.9 7.5 3.7
Gain on insurance proceeds - net 40.1 0.0 73.1 0.0
Other income (loss) - net 3.8 (5.7) (1.7) (9.1)
Income tax (expense) benefit (12.1) 1.3 (13.9) (0.3)
Equity in losses of unconsolidated subsidiaries (1.0) 0.0 (1.0) 0.0
Net income (loss) 243.8 (11.7) 570.8 10.7
Reportable Segment | Nonrelated Party        
Segment Reporting [Line Items]        
Interest expense (9.5) (9.8) (19.4) (19.8)
Net gain (loss) on forward and derivative contracts - nonaffiliates 7.1 (15.6) (58.2) (21.0)
Reportable Segment | Related Party        
Segment Reporting [Line Items]        
Interest expense $ (0.6) $ (1.9) $ (1.2) $ (3.7)