Investments (Summary of Changes in Fair Value of the Nuclear Decommissioning Trusts) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Summary Of Changes In The Fair Value [Roll Forward]
Balance at beginning of period	$ 4,242
Balance at end of period	4,352
Southern California Edison
Summary Of Changes In The Fair Value [Roll Forward]
Balance at beginning of period	4,242	$ 4,331
Gross realized gains	99	17
Gross realized losses	(16)	(3)
Unrealized gains, net of losses	27	59
Other-than-temporary impairments	(1)	(7)
Interest and dividends	28	29
Income taxes	0	(18)
Decommissioning disbursements	(26)	(116)
Administrative expenses and other	(1)	(2)
Balance at end of period	$ 4,352	$ 4,290