Income Taxes (Components of Net Accumulated Deferred Income Tax Liability) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Property and software related	$ 358	$ 549
Nuclear decommissioning trust assets in excess of nuclear ARO liability	404	348
Loss and credit carryforwards	1,346	1,418
Regulatory asset	812	15
Pension and postretirement benefits other than pensions	214	300
Other	277	419
Sub-total	3,411	3,049
Less valuation allowance	28	24
Total	3,383	3,025
Deferred tax liabilities:
Property-related	6,970	10,330
Capitalized software costs	160	237
Regulatory liability	158	134
Nuclear decommissioning trust assets	404	348
Postretirement benefits other than pensions	36	13
Other	140	202
Total	7,868	11,264
Accumulated deferred income tax liability, net	4,485	8,239
Recorded valuation allowance	28
Unrecognized tax benefits	432	471	$ 529	$ 576
Regulatory asset	809
Loss And Credit Carryforwards
Deferred tax liabilities:
Unrecognized tax benefits	77
SCE
Deferred tax assets:
Property and software related	357	548
Nuclear decommissioning trust assets in excess of nuclear ARO liability	404	348
Loss and credit carryforwards	150	0
Regulatory asset	812	15
Pension and postretirement benefits other than pensions	86	93
Other	236	408
Sub-total	2,045	1,412
Less valuation allowance	0	0
Total	2,045	1,412
Deferred tax liabilities:
Property-related	6,962	10,330
Capitalized software costs	160	237
Regulatory liability	158	134
Nuclear decommissioning trust assets	404	348
Postretirement benefits other than pensions	36	13
Other	133	148
Total	7,853	11,210
Accumulated deferred income tax liability, net	5,808	9,798
Unrecognized tax benefits	331	$ 371	$ 353	$ 441
SCE | Loss And Credit Carryforwards
Deferred tax liabilities:
Unrecognized tax benefits	$ 75