REGULATORY ASSETS, LIABILITIES, AND BALANCING ACCOUNTS (Long-Term Regulatory Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 8,978	$ 6,066
Utility retained generation asset costs	1,200
Pension benefits
Regulatory Assets [Line Items]
Total long-term regulatory assets	2,245	1,823
Environmental compliance costs
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 1,112	1,062
Recovery Period	32 years
Utility retained generation
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 181	228
Recovery Period	6 years
Price risk management
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 204	124
Recovery Period	19 years
Unamortized loss, net of gain, on reacquired debt
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 49	63
Recovery Period	23 years
Catastrophic event memorandum account
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 842	656
Catastrophic event memorandum account | COVID-19
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 49
Catastrophic event memorandum account | Minimum
Regulatory Assets [Line Items]
Recovery Period	1 year
Catastrophic event memorandum account | Maximum
Regulatory Assets [Line Items]
Recovery Period	3 years
Wildfire expense memorandum account
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 400	423
Wildfire expense memorandum account | Minimum
Regulatory Assets [Line Items]
Recovery Period	1 year
Wildfire expense memorandum account | Maximum
Regulatory Assets [Line Items]
Recovery Period	3 years
Fire hazard prevention memorandum account
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 137	259
Fire hazard prevention memorandum account | Minimum
Regulatory Assets [Line Items]
Recovery Period	1 year
Fire hazard prevention memorandum account | Maximum
Regulatory Assets [Line Items]
Recovery Period	3 years
Fire risk mitigation memorandum account
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 66	95
Fire risk mitigation memorandum account | Minimum
Regulatory Assets [Line Items]
Recovery Period	1 year
Fire risk mitigation memorandum account | Maximum
Regulatory Assets [Line Items]
Recovery Period	3 years
Wildfire mitigation plan memorandum account
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 390	558
Wildfire mitigation plan memorandum account | Minimum
Regulatory Assets [Line Items]
Recovery Period	1 year
Wildfire mitigation plan memorandum account | Maximum
Regulatory Assets [Line Items]
Recovery Period	3 years
Deferred income tax
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 908	252
Recovery Period	51 years
Insurance premium costs
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 294	0
Insurance premium costs | Minimum
Regulatory Assets [Line Items]
Recovery Period	1 year
Insurance premium costs | Maximum
Regulatory Assets [Line Items]
Recovery Period	4 years
Wildfire mitigation balancing account
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 156	0
Wildfire mitigation balancing account | Minimum
Regulatory Assets [Line Items]
Recovery Period	1 year
Cost percentage threshold requiring approval	115.00%
Wildfire mitigation balancing account | Maximum
Regulatory Assets [Line Items]
Recovery Period	3 years
General rate case memorandum accounts
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 376	0
General rate case memorandum accounts | Minimum
Regulatory Assets [Line Items]
Recovery Period	1 year
General rate case memorandum accounts | Maximum
Regulatory Assets [Line Items]
Recovery Period	2 years
Vegetation management balancing account
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 592	0
Vegetation management balancing account | Minimum
Regulatory Assets [Line Items]
Recovery Period	1 year
Cost percentage threshold requiring approval	120.00%
Vegetation management balancing account | Maximum
Regulatory Assets [Line Items]
Recovery Period	3 years
COVID-19 Pandemic protection memorandum account
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 84	0
COVID-19 pandemic protection memorandum account, undercollection bad debt
Regulatory Assets [Line Items]
Total long-term regulatory assets	76
COVID-19 pandemic protection memorandum account, program and accounts receivable financing costs
Regulatory Assets [Line Items]
Total long-term regulatory assets	8
Other
Regulatory Assets [Line Items]
Total long-term regulatory assets	$ 942	$ 523