FAIR VALUE MEASUREMENTS - ASSETS AND LIABILITIES MEASURED ON A RECURRING BASIS (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025
Assets
Derivative assets	$ 17.0	$ 7.9
Liabilities
Derivative liabilities	6.6	4.0
Fair value measurements on a recurring basis
Assets
Derivative assets	17.0	7.9
Fair value measurements on a recurring basis \| Level 1
Assets
Derivative assets	0.3	0.1
Fair value measurements on a recurring basis \| Level 2
Assets
Derivative assets	6.5	5.5
Fair value measurements on a recurring basis \| Level 3
Assets
Derivative assets	10.2	2.3
Fair value measurements on a recurring basis \| Natural gas contracts
Assets
Derivative assets	6.8	5.6
Liabilities
Derivative liabilities	6.6	4.0
Fair value measurements on a recurring basis \| Natural gas contracts \| Level 1
Assets
Derivative assets	0.3	0.1
Liabilities
Derivative liabilities	5.4	3.4
Fair value measurements on a recurring basis \| Natural gas contracts \| Level 2
Assets
Derivative assets	6.5	5.5
Liabilities
Derivative liabilities	1.2	0.6
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	10.2	2.3
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	$ 10.2	$ 2.3