Summary of Significant Accounting Policies (Emission Allowances) (Details) - SCE - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Significant Accounting Policies [Line Items]
Regulatory liabilities	$ 9,861	$ 9,735
LCFS net sales proceeds
Significant Accounting Policies [Line Items]
Regulatory liabilities	103	24
Other Current Assets
Significant Accounting Policies [Line Items]
GHG allowances	38	127
Other Current Liabilities
Significant Accounting Policies [Line Items]
GHG emission obligations	$ 30	$ 129