Accounting for Derivative Instruments and Hedging Activities (Schedule of Derivative Assets and Liabilities) (Details) $ in Thousands, MWh in Millions, MMBTU in Millions	Dec. 31, 2021 USD ($) MMBTU MWh	Dec. 31, 2020 USD ($) MMBTU MWh
Derivative [Line Items]
Assets, Current	$ 128,210	$ 33,015
Assets, Long-term	26,197	8,805
Liabilities, Current	63,309	31,441
Liabilities, Long-term	40,965	29,833
Not Designated as Hedging Instrument
Derivative [Line Items]
Total derivative assets	154,407	41,820
Total derivative liabilities	104,274	61,274
Not Designated as Hedging Instrument | Parent Company [Member]
Derivative [Line Items]
Assets, Current	128,210	33,015
Assets, Long-term	26,197	8,805
Liabilities, Current	63,309	31,441
Liabilities, Long-term	$ 40,965	$ 29,833
Not Designated as Hedging Instrument | Electric Generation Fuel
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU	238.0	212.2
Not Designated as Hedging Instrument | Purchased Electricity
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MWh	8.1	6.6
Not Designated as Hedging Instrument | Natural Gas Portfolio
Derivative [Line Items]
Total derivative assets	$ 79,578	$ 19,276
Total derivative liabilities	18,850	14,352
Not Designated as Hedging Instrument | Electric Portfolio
Derivative [Line Items]
Total derivative assets	74,829	22,544
Total derivative liabilities	$ 85,424	$ 46,922
Not Designated as Hedging Instrument | Gas Derivatives
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU	347.0	320.0