FAIR VALUE MEASUREMENTS - ASSETS AND LIABILITIES MEASURED ON A RECURRING BASIS (Details) - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025
Assets
Derivative assets	$ 8.6	$ 6.2
Liabilities
Derivative liabilities	16.6	7.7
Fair value measurements on a recurring basis
Assets
Derivative assets	8.6	6.2
Fair value measurements on a recurring basis \| Level 1
Assets
Derivative assets	0.5	0.2
Fair value measurements on a recurring basis \| Level 2
Assets
Derivative assets	1.3	3.1
Fair value measurements on a recurring basis \| Level 3
Assets
Derivative assets	6.8	2.9
Fair value measurements on a recurring basis \| Natural gas contracts
Assets
Derivative assets	1.8	3.3
Liabilities
Derivative liabilities	16.6	7.7
Fair value measurements on a recurring basis \| Natural gas contracts \| Level 1
Assets
Derivative assets	0.5	0.2
Liabilities
Derivative liabilities	14.9	5.9
Fair value measurements on a recurring basis \| Natural gas contracts \| Level 2
Assets
Derivative assets	1.3	3.1
Liabilities
Derivative liabilities	1.7	1.8
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	2.9
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	$ 2.9