REGULATORY ASSETS, LIABILITIES, AND BALANCING ACCOUNTS (Long-Term Regulatory Assets) (Details) - USD ($) $ in Millions	3 Months Ended	15 Months Ended
	Mar. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 9,159	$ 9,159	$ 8,978
Retained generation asset costs	1,200	1,200
Pension benefits
Regulatory Assets [Line Items]
Total long-term regulatory assets	2,208	2,208	2,245
Environmental compliance costs
Regulatory Assets [Line Items]
Total long-term regulatory assets	1,038	1,038	1,112
Utility retained generation
Regulatory Assets [Line Items]
Total long-term regulatory assets	168	168	181
Price risk management
Regulatory Assets [Line Items]
Total long-term regulatory assets	228	228	204
Unamortized loss, net of gain, on reacquired debt
Regulatory Assets [Line Items]
Total long-term regulatory assets	46	46	49
Catastrophic event memorandum account
Regulatory Assets [Line Items]
Total long-term regulatory assets	879	879	842
Catastrophic event memorandum account | COVID-19
Regulatory Assets [Line Items]
Total long-term regulatory assets	54	54
Wildfire expense memorandum account
Regulatory Assets [Line Items]
Total long-term regulatory assets	393	393	400
Fire hazard prevention memorandum account
Regulatory Assets [Line Items]
Total long-term regulatory assets	107	107	137
Fire risk mitigation memorandum account
Regulatory Assets [Line Items]
Total long-term regulatory assets	58	58	66
Wildfire mitigation plan memorandum account
Regulatory Assets [Line Items]
Total long-term regulatory assets	359	359	390
Deferred income taxes
Regulatory Assets [Line Items]
Total long-term regulatory assets	1,075	1,075	908
Insurance premium costs
Regulatory Assets [Line Items]
Total long-term regulatory assets	225	225	294
Wildfire mitigation balancing account
Regulatory Assets [Line Items]
Total long-term regulatory assets	156	$ 156	156
Wildfire mitigation balancing account | Minimum
Regulatory Assets [Line Items]
Cost percentage threshold requiring approval		115.00%
General rate case memorandum accounts
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 349	$ 349	376
Recovery period	22 months
Vegetation management balancing account
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 594	594	592
Vegetation management balancing account | Minimum
Regulatory Assets [Line Items]
Cost percentage threshold requiring approval	120.00%
COVID-19 pandemic protection memorandum account
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 132	132	84
COVID-19 pandemic protection memorandum account, undercollection bad debt
Regulatory Assets [Line Items]
Total long-term regulatory assets	122	122
COVID-19 pandemic protection memorandum account, program and accounts receivable financing costs
Regulatory Assets [Line Items]
Total long-term regulatory assets	10	10
Other
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 1,144	$ 1,144	$ 942