Summary of Significant Accounting Policies (Property, Plant and Equipment) (Details) - SCE - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Depreciation	$ 1,610	$ 1,520	$ 1,420
Depreciation expense stated as a percent of average original cost of depreciable utility plant (percent)	3.80%	3.80%	3.90%
AFUDC equity capitalized during construction	$ 87	$ 74	$ 87
Interest and other income
Property, Plant and Equipment [Line Items]
AFUDC equity capitalized during construction	87	74	87
Interest expense
Property, Plant and Equipment [Line Items]
AFUDC debt capitalized during construction	$ 28	$ 23	$ 31
Generation plant
Property, Plant and Equipment [Line Items]
Weighted-Average Useful Lives	37 years
Distribution plant
Property, Plant and Equipment [Line Items]
Weighted-Average Useful Lives	43 years
Transmission plant
Property, Plant and Equipment [Line Items]
Weighted-Average Useful Lives	52 years
General plant and other
Property, Plant and Equipment [Line Items]
Weighted-Average Useful Lives	22 years
Minimum | Generation plant
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	10 years
Minimum | Distribution plant
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	20 years
Minimum | Transmission plant
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	40 years
Minimum | General plant and other
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	5 years
Maximum | Generation plant
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	55 years
Maximum | Distribution plant
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	60 years
Maximum | Transmission plant
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	65 years
Maximum | General plant and other
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	60 years