FAIR VALUE MEASUREMENTS - ASSETS AND LIABILITIES MEASURED ON A RECURRING BASIS (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
Assets
Derivative assets	$ 13.5	$ 8.1
Liabilities
Derivative liabilities	2.3	0.9
Fair value measurements on a recurring basis
Assets
Derivative assets	13.5	8.1
Fair value measurements on a recurring basis | Level 1
Assets
Derivative assets	2.3	3.3
Fair value measurements on a recurring basis | Level 2
Assets
Derivative assets	4.9	2.8
Fair value measurements on a recurring basis | Level 3
Assets
Derivative assets	6.3	2.0
Fair value measurements on a recurring basis | Natural gas contracts
Assets
Derivative assets	7.2	6.1
Liabilities
Derivative liabilities	2.3	0.9
Fair value measurements on a recurring basis | Natural gas contracts | Level 1
Assets
Derivative assets	2.3	3.3
Liabilities
Derivative liabilities	1.2	0.6
Fair value measurements on a recurring basis | Natural gas contracts | Level 2
Assets
Derivative assets	4.9	2.8
Liabilities
Derivative liabilities	1.1	0.3
Fair value measurements on a recurring basis | Natural gas contracts | Level 3
Assets
Derivative assets	0.0	0.0
Liabilities
Derivative liabilities	0.0	0.0
Fair value measurements on a recurring basis | FTRs
Assets
Derivative assets	6.3	2.0
Fair value measurements on a recurring basis | FTRs | Level 1
Assets
Derivative assets	0.0	0.0
Fair value measurements on a recurring basis | FTRs | Level 2
Assets
Derivative assets	0.0	0.0
Fair value measurements on a recurring basis | FTRs | Level 3
Assets
Derivative assets	$ 6.3	$ 2.0