Summary of Significant Accounting Policies (New Accounting Guidance) (Details) - USD ($) $ in Millions	Jan. 01, 2019	Mar. 31, 2019	Jan. 31, 2019	Dec. 31, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
ROU assets		$ 933		$ 0
Southern California Edison
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
ROU assets		928		$ 0
ROU lease liability		$ 928
ASU 2016-02
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
ROU assets	$ 956
ROU lease liability			$ 956
ASU 2016-02 | Southern California Edison
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
ROU assets	951
ROU lease liability			$ 951
ASU 2018-02
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Reclassification of stranded tax effects	10
ASU 2018-02 | Southern California Edison
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Reclassification of stranded tax effects	$ 5