Summary of Significant Accounting Policies (Uncollectible Allowance) (Details) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Jun. 30, 2021 USD ($) D	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Gross long-term account receivables		$ 199		$ 199
Allowance for long-term uncollectible accounts		93		93
SCE
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		270	$ 90	188	$ 49
Included in operation and maintenance expenses in earning activities		13	15	38	50
Included in operation and maintenance expenses in cost-recovery activities		52		112
Deferred to regulatory memorandum accounts		7	43	13	64
Less: write-offs, net of recoveries		4	7	13	22
Ending balance	$ 270	338	141	338	141
Number of arrearages days | D	60
Term of payment plans	24 months
Allowance for long-term uncollectible accounts		93		93
SCE | Customers
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		254	75	175	35
Included in operation and maintenance expenses in earning activities		9	11	27	39
Included in operation and maintenance expenses in cost-recovery activities		52		112
Deferred to regulatory memorandum accounts		7	43	13	64
Less: write-offs, net of recoveries		1	5	6	14
Ending balance	$ 254	321	124	321	124
SCE | All others
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		16	15	13	14
Included in operation and maintenance expenses in earning activities		4	4	11	11
Less: write-offs, net of recoveries		3	2	7	8
Ending balance	$ 16	$ 17	$ 17	$ 17	$ 17