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Derivative Instruments (Notional Values) (Details) - Southern California Edison - Electric Utility - Economic Hedges MWh in Thousands, GWh in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2018 Bcfe MWh GWh | Dec. 31, 2017 Bcfe MWh GWh
Electricity options, swaps and forwards (GWh) |  |
Derivative [Line Items] |  |
Notional volumes of derivative instruments | MWh | 542 | 475
Natural gas options, swaps and forwards (Bcf) |  |
Derivative [Line Items] |  |
Notional volumes of derivative instruments | Bcfe | 135 | 143
Congestion revenue rights (GWh) |  |
Derivative [Line Items] |  |
Notional volumes of derivative instruments | GWh | 64,830 | 78,765

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