Investments (Summary of Changes in Fair Value of the Nuclear Decommissioning Trusts) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Summary Of Changes In The Fair Value [Roll Forward]
Balance at beginning of period			$ 4,242
Balance at end of period	$ 4,415		4,415
Southern California Edison
Summary Of Changes In The Fair Value [Roll Forward]
Balance at beginning of period	4,381	$ 4,344	4,242	$ 4,331
Gross realized gains	22	18	134	61
Gross realized losses	(3)	(1)	(19)	(5)
Unrealized gains, net of losses	65	32	179	153
Other-than-temporary impairments	(2)	(2)	(6)	(10)
Interest and dividends	28	28	87	88
Income taxes	(9)	(5)	(35)	(47)
Decommissioning disbursements	(65)	(38)	(164)	(192)
Administrative expenses and other	(2)	0	(3)	(3)
Balance at end of period	$ 4,415	$ 4,376	$ 4,415	$ 4,376