v3.26.1
FAIR VALUE MEASUREMENTS (Measured on Recurring Basis) (Details) - USD ($)
$ in Millions
Jun. 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 $ (9.6) $ (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 10.6 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 100.3 9.7
Derivative liability, effect of counter-party netting (100.3) (9.7)
Derivative Liability 0.0 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 84.6 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 15.7 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 0.0 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 503.9 574.8
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 503.9 574.8
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 6.1 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 6.1 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 133.2 20.1
Derivative assets, effect of counter-party netting (100.3) (9.7)
Derivative assets, net carrying value 32.9 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 122.2 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 11.0 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 $ 0.0 $ 0.0