Summary of Significant Accounting Policies (New Accounting Guidance) (Details) - USD ($) $ in Millions		3 Months Ended
	Jan. 01, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Retained earnings		$ 9,211		$ 9,188
Net periodic benefit income (costs) - non-service cost components			$ 8
Southern California Edison
Defined Benefit Plan Disclosure [Line Items]
Retained earnings		9,684		$ 9,607
Net periodic benefit income (costs) - non-service cost components		$ 26	$ 9
ASU 2014-09 | Difference between revenue guidance in effect before and after topic 606
Defined Benefit Plan Disclosure [Line Items]
Retained earnings	$ 5
Retained earnings, before tax	7
ASU 2016-07
Defined Benefit Plan Disclosure [Line Items]
Retained earnings	5
Retained earnings, before tax	$ 8