Commitments and Contingencies (Environmental Remediation) (Details) - SCE $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) site	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Jointly Owned Utility Plant Interests [Line Items]
Identified material sites (number) | site	20
Minimum estimated liability	$ 1
Recorded estimated minimum liability	$ 150
Immaterial sites (number) | site	16
Environmental remediation regulatory assets	$ 144
Expected recovery from incentive mechanism	$ 49
Expected recovery from incentive mechanism (percent)	90.00%
Recovery through customer rates	$ 95
Recovery through customer rates (percent)	100.00%
Cost may exceed recorded liability, material sites	$ 129
Cost may exceed recorded liability, immaterial sites	$ 8
Clean up (period)	30 years
Expected remediation costs for each of the next four years, low end of range	$ 5
Expected remediation costs for each of the next four years, high end of range	21
Environmental remediation expense	9	$ 4	$ 5
San Onofre
Jointly Owned Utility Plant Interests [Line Items]
Recorded estimated minimum liability	93
Material sites
Jointly Owned Utility Plant Interests [Line Items]
Recorded estimated minimum liability	146
Immaterial sites | Minimum
Jointly Owned Utility Plant Interests [Line Items]
Recorded estimated minimum liability	$ 4