Commitments and Contingencies (Environmental Remediation) (Details) - Southern California Edison	9 Months Ended
	Sep. 30, 2017 USD ($) site	Sep. 30, 2016 USD ($)
Schedule Of Commitments And Contingencies [Line Items]
Identified material sites for environmental remediation (in number of sites) | site	19
Minimum costs to be identified site	$ 1,000,000
Minimum liability for environmental remediation for material sites	$ 125,000,000
Immaterial sites for environmental remediation (in number of sites) | site	17
Environmental remediation liability	$ 129,000,000
Regulatory assets related to environmental remediation	123,000,000
Portion of recorded liability recoverable from incentive mechanism	$ 46,000,000
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	$ 77,000,000
Environmental remediation costs to be recovered (as a percent)	100.00%
Amount that cleanup costs could exceed recorded liability for identified material sites	$ 151,000,000
Amount that cleanup costs could exceed recorded liability for immaterial sites	$ 8,000,000
Remediation cost estimates (period)	5 years
Environmental remediation costs	$ 6,000,000	$ 3,000,000
Minimum
Schedule Of Commitments And Contingencies [Line Items]
Minimum liability for environmental remediation for immaterial sites	4,000,000
Expected annual environmental remediation costs	$ 5,000,000
Maximum
Schedule Of Commitments And Contingencies [Line Items]
Maximum expected period for cleanup of identified sites (in years)	30 years
Expected annual environmental remediation costs	$ 17,000,000
San Onofre
Schedule Of Commitments And Contingencies [Line Items]
Minimum liability for environmental remediation for material sites	$ 74,000,000