Derivative Instruments and Hedging Activities (Details) MWh in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021 USD ($) MWh	Mar. 31, 2021 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Jun. 30, 2021 USD ($) MWh	Jun. 30, 2020 USD ($)	Aug. 02, 2021	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Other Comprehensive Income (Loss), Net of Tax	$ (15,767,000)	$ 29,594,000	$ (2,682,000)	$ (36,313,000)	$ 13,827,000	$ (38,995,000)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	(17,143,000)		(4,026,000)		12,907,000	(40,339,000)
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent	1,376,000		1,344,000		920,000	1,344,000
Accumulated Other Comprehensive Income (Loss), Net of Tax	(29,593,000)				(29,593,000)			$ (43,420,000)	$ (19,750,000)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(17,143,000)		(4,026,000)		12,907,000	(40,339,000)
Regulatory assets	62,188,000				62,188,000			45,430,000
Regulatory assets	$ 62,188,000				$ 62,188,000			45,430,000
Subsequent Event [Member]
AES Indiana energy storage facility MWh planned to acquire							180
AES Indiana solar MW planned to acquire							250
AES Indiana energy storage facility MWh planned to acquire							180
FTR [Member] | Not Designated as Hedging Instrument [Member]
Purchase of Units Derivative Instruments Financial Transmission Rights | MWh	13,182				13,182
Sale of Units Derivative Instruments Financial Transmission Rights | MWh	0				0
Derivative, Nonmonetary Notional Amount, Purchase (Sales), Net | MWh	13,182				13,182
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Purchase of Derivative Instruments Interest Rate Swap	$ 400,000,000				$ 400,000,000
Sale of Derivative Instruments Interest Rate Swap	0				0
Derivative, Notional Amount, Purchase (Sales), Net	400,000,000				400,000,000
Interest Rate Contract [Member]
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	(29,593,000)	$ (13,826,000)	$ (58,745,000)	$ (56,063,000)	(29,593,000)	$ (58,745,000)
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	$ (5,375,000)				$ (5,375,000)
Maximum Length of Time Hedged in Cash Flow Hedge					39 months
Forward power contracts | Not Designated as Hedging Instrument [Member]
Purchase of Units Derivative Instruments Financial Transmission Rights | MWh	399				399
Sale of Units Derivative Instruments Financial Transmission Rights | MWh	0				0
Derivative, Nonmonetary Notional Amount, Purchase (Sales), Net | MWh	399				399
Unrealized Gain (Loss) on Derivatives	$ 2,700,000				$ 2,700,000
Realized Gain (Loss) on Derivatives	800,000				800,000
Unrealized Gain (Loss) on Derivatives	2,700,000				2,700,000
Realized Gain (Loss) on Derivatives	800,000				800,000
Other Current Assets [Member] | FTR [Member] | Not Designated as Hedging Instrument [Member]
Derivative Asset, Fair Value, Gross Asset								543,000
Other Current Assets [Member] | Forward power contracts | Not Designated as Hedging Instrument [Member]
Derivative Asset, Fair Value, Gross Asset								0
Derivative Liability, Noncurrent | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative Liability, Fair Value, Gross Liability	$ 46,015,000				$ 46,015,000			$ 63,215,000