Accounting for Derivative Instruments and Hedging Activities Narrative (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021 USD ($)
Subsidiaries [Member]
Derivative [Line Items]
Hedging strategy number of years extended	3 years
Natural Gas Portfolio [Member]
Derivative [Line Items]
Posted Collateral	$ 2.0
External Credit Rating, Investment Grade [Member]
Derivative [Line Items]
Derivative, Credit Risk Exposure, Percentage	99.40%
External Credit Rating, Non Investment Grade [Member]
Derivative [Line Items]
Derivative, Credit Risk Exposure, Percentage	0.60%
Credit Rating [Member] | Natural Gas Portfolio [Member]
Derivative [Line Items]
Posted Collateral	$ 1.0