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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Trust I
Variable Interest Entity
Dividend income		$ 1		$ 14
Dividend distributions		1		14
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	12
Dividend distributions	4	4	12	12
Trust VI
Variable Interest Entity
Dividend income	6	6	18	6
Dividend distributions	$ 6	$ 6	$ 18	$ 6