Fair Value Measurements (Quantitative Information About Level 3 Fair Value Measurements) (Details) - Southern California Edison - Level 3 - Congestion revenue rights - Auction prices $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019 USD ($) $ / MWh	Dec. 31, 2018 USD ($) $ / MWh
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value, Assets | $	$ 95	$ 141
Fair Value, Liabilities | $	$ 0	$ 0
CAISO CRR auction prices | Minimum
Quantitative Information About Level 3 Measurements [Line Items]
Fair value inputs, price level ($ per MWh)	(7.02)	(7.41)
CAISO CRR auction prices | Maximum
Quantitative Information About Level 3 Measurements [Line Items]
Fair value inputs, price level ($ per MWh)	41.52	41.52
CAISO CRR auction prices | Average
Quantitative Information About Level 3 Measurements [Line Items]
Fair value inputs, price level ($ per MWh)	(1.43)	(1.62)