SAN ONOFRE NUCLEAR GENERATING STATION - NUCLEAR DECOMMISSIONING TRUSTS (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2017	Jan. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Anticipated term of dismantlement work		10 years
Cost	$ 697	$ 697			$ 701
Gross unrealized gains	327	327			336
Gross unrealized losses	(7)	(7)			(4)
Estimated fair value	1,017	1,017			1,033
Proceeds from sales		210	$ 357
Gross realized gains		4	45
Gross realized losses		(3)	$ (5)
Total debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	506	506			514
Gross unrealized gains	6	6			10
Gross unrealized losses	(5)	(5)			(3)
Estimated fair value	507	507			521
U.S. government corporations and agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	44	44			54
Gross unrealized gains	0	0			0
Gross unrealized losses	0	0			0
Estimated fair value	44	44			54
Municipal bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	245	245			245
Gross unrealized gains	4	4			7
Gross unrealized losses	(2)	(2)			(2)
Estimated fair value	247	247			250
Other securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	217	217			215
Gross unrealized gains	2	2			3
Gross unrealized losses	(3)	(3)			(1)
Estimated fair value	216	216			217
Equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	172	172			171
Gross unrealized gains	321	321			326
Gross unrealized losses	(2)	(2)			(1)
Estimated fair value	491	491			496
Cash and cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	19	19			16
Gross unrealized gains	0	0			0
Gross unrealized losses	0	0			0
Estimated fair value	$ 19	$ 19			$ 16
San Diego Gas and Electric Company [Member]
Schedule of Available-for-sale Securities [Line Items]
Percent of dismantlement work expense	20.00%	20.00%
Authorized recovery amount, nuclear decommissioning trust funding	$ 362	$ 362		$ 60
SONGS 1 Decommissioning [Member]
Schedule of Available-for-sale Securities [Line Items]
Environmental exit costs, anticipated cost	207
SONGS 1 Decommissioning [Member] | San Diego Gas and Electric Company [Member]
Schedule of Available-for-sale Securities [Line Items]
Environmental exit costs, anticipated cost	41
Environmental Exit Costs, Anticipated Internal Costs	3
SONGS 2 and 3 Decommissioning [Member]
Schedule of Available-for-sale Securities [Line Items]
Environmental exit costs, anticipated cost	3,200
SONGS 2 and 3 Decommissioning [Member] | San Diego Gas and Electric Company [Member]
Schedule of Available-for-sale Securities [Line Items]
Environmental exit costs, anticipated cost	638
Environmental Exit Costs, Anticipated Internal Costs	$ 43