Derivative Instruments (Notional Values) (Details) - Southern California Edison - Electric Utility - Economic Hedges MWh in Thousands, GWh in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018 Bcfe MWh GWh	Dec. 31, 2017 Bcfe MWh GWh
Electricity options, swaps and forwards (GWh)
Derivative [Line Items]
Notional volumes of derivative instruments | MWh	542	475
Natural gas options, swaps and forwards (Bcf)
Derivative [Line Items]
Notional volumes of derivative instruments | Bcfe	135	143
Congestion revenue rights (GWh)
Derivative [Line Items]
Notional volumes of derivative instruments | GWh	64,830	78,765