SIGNIFICANT ACCOUNTING POLICIES AND OTHER FINANCIAL DATA - GOODWILL AND OTHER INTANGIBLE ASSETS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 0.0	$ 1,602.0
Total intangible assets, gross		440.0
Accumulated amortization		(148.0)
Other intangible assets	0.0	292.0
Intangible assets amortization expense	19.0	26.0	$ 26.0
Amortization recorded against revenues	10.0	13.5	$ 13.5
Disposal Group Held-for-sale | SI Partners
Finite-Lived Intangible Assets [Line Items]
Goodwill	1,602.0
Other intangible assets	273.0
Disposal group, gross other intangible assets	440.0
Disposal group, other intangible assets, accumulated amortization	$ 167.0
Renewable energy transmission and consumption permits
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross		169.0
Accumulated amortization		(68.0)
O&M agreement
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross		66.0
Accumulated amortization		(20.0)
ESJ PPA
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross		190.0
Accumulated amortization		(51.0)
Other
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross		15.0
Accumulated amortization		$ (9.0)