Investments (Nuclear Decommissioning Trusts) (Details) - SCE - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investment Holdings [Line Items]
Unrealized holding gains, net of losses	$ 1,600	$ 1,500
Other-than-temporary impairments	143	170
Deferred income taxes related to unrealized gains	404
Nuclear decommissioning trusts	4,000
Gross realized gains	244	92	$ 326
Gross realized losses	$ (23)	$ (19)	$ (26)