SIGNIFICANT ACCOUNTING POLICIES AND OTHER FINANCIAL DATA - OTHER INTANGIBLE ASSETS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 1,602	$ 1,602
Total intangible assets, gross	250	250
Accumulated amortization	(48)	(37)
Other intangible assets	202	213
Intangible assets amortization expense	11	11	$ 16
Expected amortization, year one	12
Expected amortization, year two	12
Expected amortization, year three	12
Expected amortization, year four	12
Expected amortization, year five	$ 12
Renewable energy and consumption permit [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization period	19 years
Intangible assets, gross	$ 154	154
Accumulated amortization	$ (32)	(24)
O&M agreement [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization period	23 years
Intangible assets, gross	$ 66	66
Accumulated amortization	(9)	(6)
Other [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	30	30
Accumulated amortization	$ (7)	$ (7)
Other [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization period	10 years