SAN ONOFRE NUCLEAR GENERATING STATION - NUCLEAR DECOMMISSIONING TRUSTS (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Cost	$ 819		$ 729
Gross unrealized gains	203		360
Gross unrealized losses	(35)		(7)
Estimated fair value	987		1,082
Proceeds from sales	552	$ 225
Gross realized gains	92	5
Gross realized losses	(5)	$ (2)
Total debt securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	664		545
Gross unrealized gains	18		21
Gross unrealized losses	(13)		(1)
Estimated fair value	669		565
U.S. government corporations and agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	68		57
Gross unrealized gains	2		0
Gross unrealized losses	0		0
Estimated fair value	70		57
Municipal bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	320		270
Gross unrealized gains	12		12
Gross unrealized losses	(2)		0
Estimated fair value	330		282
Other securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	276		218
Gross unrealized gains	4		9
Gross unrealized losses	(11)		(1)
Estimated fair value	269		226
Equity securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	141		176
Gross unrealized gains	185		339
Gross unrealized losses	(22)		(6)
Estimated fair value	304		509
Cash and cash equivalents [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	14		8
Gross unrealized gains	0		0
Gross unrealized losses	0		0
Estimated fair value	$ 14		$ 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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