Summary of Significant Accounting Policies (New Accounting Guidance) (Details) - USD ($) $ in Millions			3 Months Ended		9 Months Ended
	Jan. 01, 2019	Jan. 01, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect of accounting changes					$ 5
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit income - non-service cost components				$ 8		$ 15
ASU 2014-09 | Difference between revenue guidance in effect before and after topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect of accounting changes		$ 5
Cumulative effect of accounting changes, before tax		7
ASU 2016-07
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect of accounting changes		5
Cumulative effect of accounting changes, before tax		$ 8
ASU 2018-02 | Forecast
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Reclassification of stranded tax effects	$ 10
Southern California Edison
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect of accounting changes					0
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit income - non-service cost components			$ 26	$ 9	$ 79	$ 27
Southern California Edison | ASU 2018-02 | Forecast
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Reclassification of stranded tax effects	$ 5