REGULATORY ASSETS, LIABILITIES, AND BALANCING ACCOUNTS (Long-Term Regulatory Liabilities) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	$ 11,204	$ 10,424
Proceeds received from sale of transmission tower wireless licenses, refunded to customers	471
Federal Energy Regulatory Commission (FERC)
Regulatory Liabilities [Line Items]
Proceeds received from sale of transmission tower wireless licenses, refunded to customers	333
California Public Utilities Commission (CPUC)
Regulatory Liabilities [Line Items]
Proceeds received from sale of transmission tower wireless licenses, refunded to customers	138
Cost of removal obligations
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	7,035	6,905
Recoveries in excess of AROs
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	452	458
Public purpose programs
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	983	948
Employee benefit plans
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	1,002	995
Tower Licenses
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	471	0
Other
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	$ 1,261	$ 1,118