Summary of Significant Accounting Policies (Deferred Financing Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Regulatory Assets [Line Items]
Regulatory assets	$ 7,120	$ 6,088
Amortization of deferred financing costs charged to interest expense	32	30	$ 30
Long-term debt
Regulatory Assets [Line Items]
Unamortized debt issuance expense	131	121
SCE
Regulatory Assets [Line Items]
Regulatory assets	7,120	6,088
Amortization of deferred financing costs charged to interest expense	27	26	$ 26
SCE | Long-term debt
Regulatory Assets [Line Items]
Unamortized debt issuance expense	117	106
SCE | Unamortized loss on reacquired debt
Regulatory Assets [Line Items]
Regulatory assets	$ 133	$ 142