v3.26.3
FAIR VALUE MEASUREMENTS (Measured on Recurring Basis) (Details) - USD ($)
$ in Millions
Sep. 30, 2026
Dec. 31, 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets, effect of counter-party netting $ 7.6 $ 5.7
Fair Value, Measurements, Recurring | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Non-qualified pension plan assets 19.1 18.6
Fair Value, Measurements, Recurring | Commodity contracts    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative liability, gross carrying value 208.6 9.7
Derivative liability, effect of counter-party netting (188.6) (9.7)
Derivative Liability 20.0 0.0
Fair Value, Measurements, Recurring | Commodity contracts | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative liability, gross carrying value 174.6 9.6
Fair Value, Measurements, Recurring | Commodity contracts | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative liability, gross carrying value 8.7 0.1
Fair Value, Measurements, Recurring | Commodity contracts | Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative liability, gross carrying value 25.3 0.0
Fair Value, Measurements, Recurring | Renewable energy credit and emissions obligations    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Renewable energy credit and emissions obligations 486.5 574.8
Derivative liability, effect of counter-party netting 0.0 0.0
Fair Value, Measurements, Recurring | Renewable energy credit and emissions obligations | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Renewable energy credit and emissions obligations 0.0 0.0
Fair Value, Measurements, Recurring | Renewable energy credit and emissions obligations | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Renewable energy credit and emissions obligations 486.5 574.8
Fair Value, Measurements, Recurring | Renewable energy credit and emissions obligations | Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Renewable energy credit and emissions obligations 0.0 0.0
Fair Value, Measurements, Recurring | Money market funds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents 5.9 14.2
Fair Value, Measurements, Recurring | Money market funds | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents 5.9 14.2
Fair Value, Measurements, Recurring | Money market funds | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents 0.0 0.0
Fair Value, Measurements, Recurring | Money market funds | Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents 0.0 0.0
Fair Value, Measurements, Recurring | Commodity contracts    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets, gross carrying value 188.6 20.1
Derivative assets, effect of counter-party netting 188.6 9.7
Derivative assets, net carrying value 0.0 10.4
Fair Value, Measurements, Recurring | Commodity contracts | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets, gross carrying value 180.3 8.2
Fair Value, Measurements, Recurring | Commodity contracts | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets, gross carrying value 2.1 11.9
Fair Value, Measurements, Recurring | Commodity contracts | Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets, gross carrying value $ 6.2 $ 0.0