Regulatory Assets and Liabilities (Schedule of Net Regulatory Balancing Accounts) (Details) - Southern California Edison - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Regulatory balancing accounts | Energy resource recovery account
Regulatory Assets and Liabilities
Asset (liability)	$ 452	$ 464
Regulatory balancing accounts | New system generation balancing account
Regulatory Assets and Liabilities
Asset (liability)	(190)	(197)
Refunds of excess revenue | Net regulatory balancing accounts
Regulatory Assets and Liabilities
Asset (liability)	(1,726)	(1,698)
Refunds of excess revenue | Public purpose programs and energy efficiency programs
Regulatory Assets and Liabilities
Asset (liability)	(1,270)	(1,145)
Refunds of excess revenue | Tax accounting memorandum account and pole loading balancing account
Regulatory Assets and Liabilities
Asset (liability)	4	(259)
Refunds of excess revenue | Base revenue requirement balancing account
Regulatory Assets and Liabilities
Asset (liability)	(500)	(200)
Refunds of excess revenue | DOE litigation memorandum account
Regulatory Assets and Liabilities
Asset (liability)	(191)	(156)
Refunds of excess revenue | Greenhouse gas auction revenue
Regulatory Assets and Liabilities
Asset (liability)	140	(22)
Refunds of excess revenue | FERC balancing accounts
Regulatory Assets and Liabilities
Asset (liability)	(220)	(205)
Refunds of excess revenue | Catastrophic event memorandum account
Regulatory Assets and Liabilities
Asset (liability)	109	102
Refunds of excess revenue | Other
Regulatory Assets and Liabilities
Asset (liability)	$ (60)	$ (80)