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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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The end date of the period reflected on the cover page if a periodic report. For all other reports and registration statements containing historical data, it is the date up through which that historical data is presented. If there is no historical data in the report, use the filing date. The format of the date is CCYY-MM-DD.

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Amount of loss contingency liability expected to be resolved within one year or the normal operating cycle, if longer.

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Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

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