Commitments And Contingencies (Details) - Maximum [Member] $ in Millions	Sep. 30, 2018 USD ($)
Market Manipulation Lawsuit [Member]
Loss Contingencies [Line Items]
Loss Contingency, Estimated Potential Loss	$ 16.0
2015 Washington General Rate Case [Member]
Loss Contingencies [Line Items]
Loss Contingency, Estimated Potential Loss	35.2
Electric [Member] | 2015 Washington General Rate Case [Member]
Loss Contingencies [Line Items]
Loss Contingency, Estimated Potential Loss	28.3
Natural Gas [Member] | 2015 Washington General Rate Case [Member]
Loss Contingencies [Line Items]
Loss Contingency, Estimated Potential Loss	$ 6.9