Fair Value Measurements (Quantitative Information About Level 3 Fair Value Measurements) (Details) - Southern California Edison - Level 3 - Congestion revenue rights - Auction prices $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2018 USD ($) $ / MWh	Dec. 31, 2017 USD ($) $ / MWh
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value, Assets | $	$ 52	$ 102
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) | $ / MWh	(5.49)	(9.41)
CAISO CRR auction prices | Maximum
Quantitative Information About Level 3 Measurements [Line Items]
Fair value inputs, price level ($ per MWh) | $ / MWh	8.79	8.66