Commitments and Contingencies (Environmental Remediation) (Details) - Southern California Edison $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) site	Mar. 31, 2017 USD ($)
Schedule Of Commitments And Contingencies [Line Items]
Minimum costs to be identified site	$ 1
Minimum liability for environmental remediation	146
Regulatory assets related to environmental remediation	140
Portion of recorded liability recoverable from incentive mechanism	$ 47
Percentage of environmental remediation costs recoverable through an incentive mechanism (as a percent)	90.00%
Liability incurred at majority of the remaining sites through customer rates	$ 93
Environmental remediation costs to be recovered (as a percent)	100.00%
Amount that cleanup costs could exceed recorded liability for identified material sites	$ 131
Amount that cleanup costs could exceed recorded liability for immaterial sites	$ 8
Clean up (period)	30 years
Remediation cost estimates (period)	5 years
Expected remediation costs for each of the next four years, low end of range	$ 4
Expected remediation costs for each of the next four years, high end of range	18
Environmental remediation costs	$ 4	$ 2
Material sites
Schedule Of Commitments And Contingencies [Line Items]
Identified material sites for environmental remediation (in number of sites) | site	20
Minimum liability for environmental remediation	$ 142
Immaterial sites
Schedule Of Commitments And Contingencies [Line Items]
Immaterial sites for environmental remediation (in number of sites) | site	16
Immaterial sites | Minimum
Schedule Of Commitments And Contingencies [Line Items]
Minimum liability for environmental remediation	$ 4
San Onofre
Schedule Of Commitments And Contingencies [Line Items]
Minimum liability for environmental remediation	$ 92