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Commitments and Contingencies (Environmental Remediation) (Details) - SCE $ in Millions | 12 Months Ended
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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 |  |

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