FAIR VALUE MEASUREMENTS - ASSETS AND LIABILITIES MEASURED ON A RECURRING BASIS (Details) - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025
Assets
Derivative assets	$ 11.6	$ 7.9
Liabilities
Derivative liabilities	9.8	4.0
Fair value measurements on a recurring basis
Assets
Derivative assets	11.6	7.9
Fair value measurements on a recurring basis \| Level 1
Assets
Derivative assets	0.4	0.1
Fair value measurements on a recurring basis \| Level 2
Assets
Derivative assets	4.4	5.5
Fair value measurements on a recurring basis \| Level 3
Assets
Derivative assets	6.8	2.3
Fair value measurements on a recurring basis \| Natural gas contracts
Assets
Derivative assets	4.8	5.6
Liabilities
Derivative liabilities	9.8	4.0
Fair value measurements on a recurring basis \| Natural gas contracts \| Level 1
Assets
Derivative assets	0.4	0.1
Liabilities
Derivative liabilities	8.7	3.4
Fair value measurements on a recurring basis \| Natural gas contracts \| Level 2
Assets
Derivative assets	4.4	5.5
Liabilities
Derivative liabilities	1.1	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	6.8	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	$ 6.8	$ 2.3