Summary of Significant Accounting Policies (New Accounting Guidance) (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 15	$ 15
Defined Benefit Plan Disclosure [Line Items]
Service cost	45	135
Non-service costs	(14)	(32)
Southern California Edison
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	1	1
Defined Benefit Plan Disclosure [Line Items]
Service cost	44	132
Non-service costs	$ (15)	$ (45)
Southern California Edison | Sales
Concentration Risk [Line Items]
Sales from tariff offerings, percentage of total operating revenues		95.00%