v3.26.1
FAIR VALUE MEASUREMENTS (Measured on Recurring Basis) (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets, Effect of Counter-party Netting $ (114.1) $ (5.7)
Derivative, Collateral, Obligation to Return Cash 114.1 5.7
Other Assets | Pension Benefits    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Defined benefit plan, plan assets, amount 18.6 18.6
Fair Value, Measurements, Recurring | Commodity contracts    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative liability, amount not offset against collateral 307.4 9.7
Derivative, Collateral, Right to Reclaim Cash (208.9) (9.7)
Derivative Liability 98.5 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, amount not offset against collateral 300.3 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, amount not offset against collateral 7.1 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, amount not offset against collateral 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]    
Derivative, Collateral, Right to Reclaim Cash 0.0 0.0
Obligations, Fair Value Disclosure 653.5 574.8
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]    
Obligations, Fair Value Disclosure 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]    
Obligations, Fair Value Disclosure 653.5 574.8
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]    
Obligations, Fair Value Disclosure 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 5.2 5.2
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 5.2 5.2
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, amount not offset against collateral 208.9 20.1
Derivative assets, Effect of Counter-party Netting (208.9) (9.7)
Derivative assets, Net Carrying Value on Balance Sheet 0.0 10.4
Derivative, Collateral, Obligation to Return Cash 208.9 9.7
Fair Value, Measurements, Recurring | Commodity contracts | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets, amount not offset against collateral 208.8 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, amount not offset against collateral 0.1 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, amount not offset against collateral $ 0.0 $ 0.0