SAN ONOFRE NUCLEAR GENERATING STATION (SONGS) - NUCLEAR DECOMMISSIONING TRUSTS (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 700		$ 658
Gross unrealized gains	366		372
Gross unrealized losses	(4)		(4)
Estimated fair value	1,062		1,026
Proceeds from sales	357	$ 93
Gross realized gains	45	3
Gross realized losses	(5)	$ (8)
Total debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	433		396
Gross unrealized gains	8		6
Gross unrealized losses	(2)		(3)
Estimated fair value	439		399
U.S. government corporations and agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	51		52
Gross unrealized gains	0		0
Gross unrealized losses	0		0
Estimated fair value	51		52
Municipal bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	216		203
Gross unrealized gains	6		4
Gross unrealized losses	(1)		(1)
Estimated fair value	221		206
Other securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	166		141
Gross unrealized gains	2		2
Gross unrealized losses	(1)		(2)
Estimated fair value	167		141
Equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	255		143
Gross unrealized gains	358		366
Gross unrealized losses	(2)		(1)
Estimated fair value	611		508
Cash and cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	12		119
Gross unrealized gains	0		0
Gross unrealized losses	0		0
Estimated fair value	$ 12		$ 119