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Commitments And Contingencies (Details) - USD ($) $ in Millions | 1 Months Ended | 9 Months Ended
--- | --- | ---
Feb. 28, 2016 | Sep. 30, 2019
Loss Contingencies [Line Items] |  |
Document Period End Date |  | Sep. 30, 2019
WASHINGTON | Electricity [Member] |  |
Loss Contingencies [Line Items] |  |
Public Utilities, Approved Rate Increase (Decrease), Amount | $ 8.1 |
2015 Washington General Rate Case [Member] |  |
Loss Contingencies [Line Items] |  |
Loss Contingency, Accrual, Current |  | $ 3.0
2015 Washington General Rate Case Power Supply Error [Member] |  |
Loss Contingencies [Line Items] |  |
Loss Contingency, Estimate of Possible Loss |  | 20.0
Minimum [Member] | 2015 Washington General Rate Case [Member] |  |
Loss Contingencies [Line Items] |  |
Loss Contingency, Estimate of Possible Loss |  | 3.0
Maximum [Member] | 2015 Washington General Rate Case [Member] |  |
Loss Contingencies [Line Items] |  |
Loss Contingency, Estimate of Possible Loss |  | $ 77.0

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