SAN ONOFRE NUCLEAR GENERATING STATION - NUCLEAR DECOMMISSIONING TRUSTS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Cost	$ 731	$ 729
Gross unrealized gains	290	360
Gross unrealized losses	(2)	(7)
Estimated fair value	1,019	1,082
Proceeds from sales	1,439	914	$ 890
Gross realized gains	156	24	42
Gross realized losses	(17)	(5)	$ (10)
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	64	57
Gross unrealized gains	1	0
Gross unrealized losses	0	0
Estimated fair value	65	57
Municipal bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	308	270
Gross unrealized gains	18	12
Gross unrealized losses	0	0
Estimated fair value	326	282
Other securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	253	218
Gross unrealized gains	17	9
Gross unrealized losses	0	(1)
Estimated fair value	270	226
Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	625	545
Gross unrealized gains	36	21
Gross unrealized losses	0	(1)
Estimated fair value	661	565
Equity securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	112	176
Gross unrealized gains	254	339
Gross unrealized losses	(2)	(6)
Estimated fair value	364	509
Cash and cash equivalents [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	3	16
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value	3	16
Accounts Payable
Debt Securities, Available-for-sale [Line Items]
Cost	(9)	(8)
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value	$ (9)	$ (8)