Variable Interest Entities (Summary of Trusts' Income Statement) (Details) - Variable Interest Entity, Not Primary Beneficiary - Southern California Edison - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Trust I
Variable Interest Entity
Dividend income	$ 1	$ 7	$ 14	$ 20
Dividend distributions	1	7	14	20
Trust II
Variable Interest Entity
Dividend income	5	5	15	15
Dividend distributions	5	5	15	15
Trust III
Variable Interest Entity
Dividend income	4	4	12	12
Dividend distributions	4	4	12	12
Trust IV
Variable Interest Entity
Dividend income	4	4	13	13
Dividend distributions	4	4	13	13
Trust V
Variable Interest Entity
Dividend income	4	4	12	9
Dividend distributions	4	$ 4	12	$ 9
Trust VI
Variable Interest Entity
Dividend income	6		6
Dividend distributions	$ 6		$ 6