Summary of Significant Accounting Policies (SCE Dividend Restrictions) (Details) - SCE $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Significant Accounting Policies [Line Items]
Minimum percentage of weighted-average common equity component authorization, set by CPUC (as a percent)	48.00%
Weighted-average common equity component authorization, set by CPUC remaining over number of months (in months)	13 months
After-tax charge excused from capital structure	$ 448
Period for calculation of weighted average common equity component (months)	13 months
Weighted-average common equity component of total capitalization (as a percent)	50.00%
Capacity to pay additional dividends	$ 511
Restriction on net assets	$ 14,200
Pro forma
Significant Accounting Policies [Line Items]
Weighted-average common equity component authorization, set by CPUC remaining over number of months (in months)	13 months
Period for calculation of weighted average common equity component (months)	13 months
Weighted-average common equity component of total capitalization (as a percent)	50.10%