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Summary of Significant Accounting Policies (Property, Plant and Equipment) (Details) - SCE - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Property, Plant and Equipment [Line Items] |  |  |
Depreciation | $ 1,610 | $ 1,520 | $ 1,420
Depreciation expense stated as a percent of average original cost of depreciable utility plant (percent) | 3.80% | 3.80% | 3.90%
AFUDC equity capitalized during construction | $ 87 | $ 74 | $ 87
Interest and other income |  |  |
Property, Plant and Equipment [Line Items] |  |  |
AFUDC equity capitalized during construction | 87 | 74 | 87
Interest expense |  |  |
Property, Plant and Equipment [Line Items] |  |  |
AFUDC debt capitalized during construction | $ 28 | $ 23 | $ 31
Generation plant |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Weighted-Average Useful Lives | 37 years |  |
Distribution plant |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Weighted-Average Useful Lives | 43 years |  |
Transmission plant |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Weighted-Average Useful Lives | 52 years |  |
General plant and other |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Weighted-Average Useful Lives | 22 years |  |
Minimum | Generation plant |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Estimated Useful Lives | 10 years |  |
Minimum | Distribution plant |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Estimated Useful Lives | 20 years |  |
Minimum | Transmission plant |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Estimated Useful Lives | 40 years |  |
Minimum | General plant and other |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Estimated Useful Lives | 5 years |  |
Maximum | Generation plant |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Estimated Useful Lives | 55 years |  |
Maximum | Distribution plant |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Estimated Useful Lives | 60 years |  |
Maximum | Transmission plant |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Estimated Useful Lives | 65 years |  |
Maximum | General plant and other |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Estimated Useful Lives | 60 years |  |

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- Definition The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 + Details
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