v3.26.1
Supplemental Balance Sheet Information - Schedule of Supplemental Balance Sheet Information (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Mar. 31, 2025
Trade Receivables, Net      
Accounts receivable $ 529.2 $ 423.9  
Allowance for doubtful receivables (0.6) (0.6)  
Receivables, net 528.6 423.3  
Inventories      
Finished products 134.0 156.1  
Work-in-process 316.6 316.7  
Raw materials 332.1 236.2  
Operating supplies 16.3 16.2  
Inventories 799.0 725.2  
Property, Plant and Equipment, Net      
Land and improvements 44.1 38.2  
Buildings and leasehold improvements 303.4 302.6  
Machinery and equipment 1,594.3 1,586.7  
Construction in progress 74.8 66.7  
Property, plant and equipment, gross 2,016.6 1,994.2  
Accumulated depreciation and amortization (877.2) (849.1)  
Land held for sale 0.1 0.1  
Property, plant and equipment, net 1,139.5 1,145.2  
Other Assets      
Restricted cash - Note 11 20.0 19.9 $ 20.0
Long-term replacement parts 32.3 28.5  
Net assets of Salaried VEBA 9.9 9.7  
Other 17.5 17.6  
Other assets 79.7 75.7  
Other Accrued Liabilities      
Uncleared cash disbursements 1.2 45.8  
Accrued income taxes and other taxes payable 15.0 7.8  
Accrued annual contribution to Salaried VEBA 0.0 2.9  
Accrued interest 10.8 6.9  
Current operating lease liabilities 5.9 4.8  
Current finance lease liabilities 3.4 2.3  
Current deferred compensation plan liabilities - Note 3 1.0 1.2  
Other - Note 4 19.0 19.6  
Other accrued liabilities 56.3 91.3  
Long-Term Liabilities      
Workers' compensation accrual 25.5 26.0  
Long-term environmental accrual - Note 6 17.3 17.4  
Other long-term liabilities 41.2 38.0  
Long-term liabilities $ 84.0 $ 81.4