FAIR VALUE MEASUREMENTS (Measured on Recurring Basis) (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, Effect of Counter-party Netting	$ (12.5)	$ (15.1)
Derivative, Collateral, Obligation to Return Cash	12.5	15.1
Other Assets | Pension Benefits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined benefit plan, plan assets, amount	20.0	19.4
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	25.6	14.0
Derivative, Collateral, Right to Reclaim Cash	(20.9)	(14.0)
Derivative Liability	4.7	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	25.6	14.0
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	0.0	0.0
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	493.1	465.9
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	493.1	465.9
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	8.0	12.9
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	8.0	12.9
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	20.9	16.0
Derivative assets, Effect of Counter-party Netting	(20.9)	(14.0)
Derivative assets, Net Carrying Value on Balance Sheet	0.0	2.0
Derivative, Collateral, Obligation to Return Cash	20.9	14.0
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	20.9	16.0
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	0.0	0.0
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