Income Taxes (Reconciliation of Unrecognized Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits
Balance at January 1,	$ 471	$ 529	$ 576
Tax positions taken during the current year, Increases	51	36	54
Tax positions taken during a prior year, Increases	0	2	66
Tax positions taken during a prior year, Decreases	(7)	(96)	(165)
Tax positions taken during a prior year, Decreases for settlements during the period	(83)	0	(2)
Balance at December 31,	432	471	529
SCE
Reconciliation of Unrecognized Tax Benefits
Balance at January 1,	371	353	441
Tax positions taken during the current year, Increases	51	36	48
Tax positions taken during a prior year, Increases	0	0	23
Tax positions taken during a prior year, Decreases	(13)	(18)	(159)
Tax positions taken during a prior year, Decreases for settlements during the period	(78)	0	0
Balance at December 31,	$ 331	$ 371	$ 353