SAN ONOFRE NUCLEAR GENERATING STATION - NUCLEAR DECOMMISSIONING TRUSTS (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Cost	$ 813		$ 813		$ 729
Gross unrealized gains	264		264		360
Gross unrealized losses	(15)		(15)		(7)
Estimated fair value	1,062		1,062		1,082
Proceeds from sales	245	$ 272	797	$ 497
Gross realized gains	7	8	99	13
Gross realized losses	(6)	$ (1)	(11)	$ (3)
Total debt securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	659		659		545
Gross unrealized gains	33		33		21
Gross unrealized losses	(3)		(3)		(1)
Estimated fair value	689		689		565
U.S. government corporations and agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	51		51		57
Gross unrealized gains	1		1		0
Gross unrealized losses	0		0		0
Estimated fair value	52		52		57
Municipal bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	327		327		270
Gross unrealized gains	17		17		12
Gross unrealized losses	(1)		(1)		0
Estimated fair value	343		343		282
Other securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	281		281		218
Gross unrealized gains	15		15		9
Gross unrealized losses	(2)		(2)		(1)
Estimated fair value	294		294		226
Equity securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	143		143		176
Gross unrealized gains	231		231		339
Gross unrealized losses	(12)		(12)		(6)
Estimated fair value	362		362		509
Cash and cash equivalents [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	11		11		8
Gross unrealized gains	0		0		0
Gross unrealized losses	0		0		0
Estimated fair value	$ 11		$ 11		$ 8

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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