Variable Interest Entities (Summary of Trusts' Income Statement) (Details) - SCE - Variable Interest Entity, Not Primary Beneficiary - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
SCE Trust I
Variable Interest Entity [Line Items]
Dividend income	$ 14	$ 27	$ 27
Dividend distributions	14	27	27
SCE Trust II
Variable Interest Entity [Line Items]
Dividend income	20	20	20
Dividend distributions	20	20	20
SCE Trust III
Variable Interest Entity [Line Items]
Dividend income	16	16	16
Dividend distributions	16	16	16
SCE Trust IV
Variable Interest Entity [Line Items]
Dividend income	17	17	6
Dividend distributions	17	17	$ 6
SCE Trust V
Variable Interest Entity [Line Items]
Dividend income	16	13
Dividend distributions	16	$ 13
Trust VI
Variable Interest Entity [Line Items]
Dividend income	12
Dividend distributions	$ 12