Regulatory Assets and Liabilities (Regulatory Balancing Accounts) (Details) - SCE - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Regulatory balancing accounts | Energy resource recovery account
Regulatory Assets and Liabilities
Net Regulatory Assets Pertaining to Balancing Accounts	$ 464	$ (20)
Regulatory balancing accounts | New system generation balancing account
Regulatory Assets and Liabilities
Net Regulatory Assets Pertaining to Balancing Accounts	(197)	(6)
Refunds of excess revenue | Significant components
Regulatory Assets and Liabilities
Net Regulatory Assets Pertaining to Balancing Accounts	(1,698)	(1,715)
Refunds of excess revenue | Public purpose programs and energy efficiency programs
Regulatory Assets and Liabilities
Net Regulatory Assets Pertaining to Balancing Accounts	(1,145)	(992)
Refunds of excess revenue | Base revenue requirement balancing account
Regulatory Assets and Liabilities
Net Regulatory Assets Pertaining to Balancing Accounts	(200)	(426)
Refunds of excess revenue | Tax accounting memorandum account and pole loading balancing account
Regulatory Assets and Liabilities
Net Regulatory Assets Pertaining to Balancing Accounts	(259)	(142)
Refunds of excess revenue | Department of Energy litigation memorandum account
Regulatory Assets and Liabilities
Net Regulatory Assets Pertaining to Balancing Accounts	(156)	(122)
Refunds of excess revenue | Greenhouse gas auction revenue
Regulatory Assets and Liabilities
Net Regulatory Assets Pertaining to Balancing Accounts	(22)	31
Refunds of excess revenue | FERC balancing accounts
Regulatory Assets and Liabilities
Net Regulatory Assets Pertaining to Balancing Accounts	(205)	(69)
Refunds of excess revenue | Other
Regulatory Assets and Liabilities
Net Regulatory Assets Pertaining to Balancing Accounts	$ 22	$ 31