Schedule I - Condensed Financial Information Of Registrant Schedule I - Condensed Financial Information Of Registrant (Derivative Instruments and Hedging Activities) (Details) MWh in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) MWh	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Number of Interest Rate Swaps	3
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	$ (19,750,000)	$ 0	$ 0
Interest Rate Contract [Member]
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	(19,750,000)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	(19,750,000)
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	$ 0
Maximum Length of Time Hedged in Cash Flow Hedge	7 months
Not Designated as Hedging Instrument [Member] | FTR [Member]
Purchase of Units Derivative Instruments Financial Transmission Rights | MWh	5,707
Sale of Units Derivative Instruments Financial Transmission Rights | MWh	0
Derivative, Nonmonetary Notional Amount, Purchase (Sales), Net | MWh	5,707
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Purchase of Derivative Instruments Interest Rate Swap	$ 400,000,000
Sale of Derivative Instruments Interest Rate Swap	0
Derivative, Notional Amount, Purchase (Sales), Net	$ 400,000,000
Parent Company [Member]
Number of Interest Rate Swaps	3
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	$ (19,750,000)	0	$ 0
Parent Company [Member] | Interest Rate Contract [Member]
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	(19,750,000)	$ 0
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	$ 0
Maximum Length of Time Hedged in Cash Flow Hedge	7 months
Parent Company [Member] | Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Purchase of Derivative Instruments Interest Rate Swap	$ 400,000,000
Sale of Derivative Instruments Interest Rate Swap	0
Derivative, Notional Amount, Purchase (Sales), Net	$ 400,000,000