Fair Value Measurements (Quantitative Information About Level 3 Fair Value Measurements) (Details) - SCE $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) $ / MWh MW	Dec. 31, 2016 USD ($) $ / MWh MW
Quantitative Information About Level 3 Measurements [Line Items]
Reclassified derivative liabilities | $	$ 914
Level 3
Quantitative Information About Level 3 Measurements [Line Items]
Reclassified derivative liabilities | $	$ 914
Level 3 | Congestion revenue rights | Market simulation model and auction prices
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value, Assets | $		$ 102	$ 67
Fair Value, Liabilities | $		$ 0	$ 0
Level 3 | Congestion revenue rights | Market simulation model and auction prices | Load forecast | Minimum
Quantitative Information About Level 3 Measurements [Line Items]
Fair value inputs, power units (in megawatts) | MW		5,002	3,708
Level 3 | Congestion revenue rights | Market simulation model and auction prices | Load forecast | Maximum
Quantitative Information About Level 3 Measurements [Line Items]
Fair value inputs, power units (in megawatts) | MW		22,970	22,840
Level 3 | Congestion revenue rights | Market simulation model and auction prices | Power prices | Minimum
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value Inputs, price level ($ per MWh)		(15.00)	3.65
Level 3 | Congestion revenue rights | Market simulation model and auction prices | Power prices | Maximum
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value Inputs, price level ($ per MWh)		120.00	99.58
Level 3 | Congestion revenue rights | Market simulation model and auction prices | Gas prices | Minimum
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value Inputs, price level ($ per MWh)		2.46	2.51
Level 3 | Congestion revenue rights | Market simulation model and auction prices | Gas prices | Maximum
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value Inputs, price level ($ per MWh)		4.37	4.87
Level 3 | Congestion revenue rights | Market simulation model and auction prices | CAISO CRR auction clearing prices | Minimum
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value Inputs, price level ($ per MWh)		(9.41)
Level 3 | Congestion revenue rights | Market simulation model and auction prices | CAISO CRR auction clearing prices | Maximum
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value Inputs, price level ($ per MWh)		8.66
Level 3 | Tolling3 | Option model
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value, Assets | $			$ 0
Fair Value, Liabilities | $			$ 1,154
Level 3 | Tolling3 | Option model | Power prices | Minimum
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value Inputs, price level ($ per MWh)			23.40
Expected volatility rate (as a percent)			29.00%
Level 3 | Tolling3 | Option model | Power prices | Maximum
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value Inputs, price level ($ per MWh)			51.24
Expected volatility rate (as a percent)			71.00%
Level 3 | Tolling3 | Option model | Gas prices | Minimum
Quantitative Information About Level 3 Measurements [Line Items]
Expected volatility rate (as a percent)			15.00%
Level 3 | Tolling3 | Option model | Gas prices | Maximum
Quantitative Information About Level 3 Measurements [Line Items]
Expected volatility rate (as a percent)			48.00%