SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Reclassifications Out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ (22)	$ (5)
Net current period other comprehensive income	7	(17)
Ending balance	(15)	(22)
Accumulated Other Comprehensive Income (Loss) | Pension Plan
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(39)	(22)
Net current period other comprehensive income	6	(17)
Ending balance	(33)	(39)
Accumulated Other Comprehensive Income (Loss) | PBOP Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	17	17
Net current period other comprehensive income	1	0
Ending balance	18	17
Amortization of prior service cost
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from other comprehensive income:	6	6
Amortization of prior service cost | Pension Plan
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from other comprehensive income:	(4)	(4)
Amounts reclassified from other comprehensive income, tax	2	2
Amortization of prior service cost | PBOP Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from other comprehensive income:	10	10
Amounts reclassified from other comprehensive income, tax	4	4
Amortization of net actuarial gain (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income before reclassifications:	1,144	(247)
Amounts reclassified from other comprehensive income:	(20)	(13)
Amortization of net actuarial gain (loss) | Pension Plan
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income before reclassifications:	1,007	(417)
Amounts reclassified from other comprehensive income:	4	2
Other comprehensive income before reclassifications, tax	391	162
Amounts reclassified from other comprehensive income, tax	2	1
Amortization of net actuarial gain (loss) | PBOP Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income before reclassifications:	137	170
Amounts reclassified from other comprehensive income:	(24)	(15)
Other comprehensive income before reclassifications, tax	53	66
Amounts reclassified from other comprehensive income, tax	9	6
Regulatory account transfer
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income before reclassifications:	(1,139)	230
Amounts reclassified from other comprehensive income:	16	7
Regulatory account transfer | Pension Plan
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income before reclassifications:	(1,003)	400
Amounts reclassified from other comprehensive income:	2	2
Other comprehensive income before reclassifications, tax	390	155
Amounts reclassified from other comprehensive income, tax	1	1
Regulatory account transfer | PBOP Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income before reclassifications:	(136)	(170)
Amounts reclassified from other comprehensive income:	14	5
Other comprehensive income before reclassifications, tax	53	66
Amounts reclassified from other comprehensive income, tax	$ 5	$ 2