Overview and Summary of Significant Accounting Policies (Details) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021 USD ($) generating_station MW	Mar. 31, 2021 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Jun. 30, 2021 USD ($) generating_station MW	Jun. 30, 2020 USD ($)	May 31, 2021	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 526,680	$ 558,531	$ 507,839	$ 518,761	$ 526,680	$ 507,839		$ 520,988	$ 546,476
Accumulated Other Comprehensive Income (Loss), Net of Tax	(29,593)				(29,593)			(43,420)	(19,750)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	(17,143)		(4,026)		12,907	(40,339)
Inventories	21,328				21,328			36,953
Cash and cash equivalents	$ 20,629				$ 20,629			20,502
Number of customers	514,000				514,000
Number of generating stations | generating_station	4				4
Restricted Cash and Cash Equivalents	$ 5				$ 5			6,120
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	20,634		53,251		20,634	53,251		26,622	48,552
Regulatory assets, current	60,132				60,132			58,553
Inventory, Net	81,460				81,460			95,506
Other Comprehensive Income (Loss), Net of Tax	(15,767)	29,594	(2,682)	(36,313)	13,827	(38,995)
Accounts Receivable, Allowance for Credit Loss, Current	1,553		4,053		1,553	4,053		3,155	921
Accounts Receivable, Credit Loss Expense (Reversal)					1,030	4,312
Accounts Receivable, Allowance for Credit Loss, Writeoff					(3,741)	(3,697)
Accounts Receivable, Allowance for Credit Loss, Recovery					1,109	2,517
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(29,593)				(29,593)			$ (43,420)	$ (19,750)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(17,143)		(4,026)		12,907	(40,339)
Income Tax Expense (Benefit)	4,505		5,165		14,540	14,937
Income Tax Expense (Benefit)	4,505		5,165		14,540	14,937
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent	$ 1,376		1,344		$ 920	1,344
Petersburg Unit 1 retired MW							230
Petersburg Unit 2 Planned Retirement MW in 2023					415
Indianapolis Power And Light Company [Member]
Debt Instrument [Line Items]
Electric generation capability for winter, megawatts | MW	3,475				3,475
Electric generation capability for summer, megawatts | MW	3,330				3,330
Aes U.S. Investments [Member]
Debt Instrument [Line Items]
Ownership percentage by parent (percent)	82.35%				82.35%
CDPQ [Member]
Debt Instrument [Line Items]
Ownership percentage by parent (percent)	17.65%				17.65%
Ownership interest in parent company (percent)	15.00%				15.00%
AES U.S. Holdings, LLC [Member]
Debt Instrument [Line Items]
Ownership interest in parent company (percent)	85.00%				85.00%
Harding Street [Member]
Debt Instrument [Line Items]
Amount of New Operation for Battery Storage Unit, megawatts | MW	20				20
Interest Rate Contract [Member]
Debt Instrument [Line Items]
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	$ (29,593)	$ (13,826)	(58,745)	$ (56,063)	$ (29,593)	(58,745)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Debt Instrument [Line Items]
Interest and Debt Expense	(1,807)		(1,807)		(1,204)	(1,807)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest and Debt Expense	(1,807)		(1,807)		(1,204)	(1,807)
Income Tax Expense (Benefit)	431		463		284	463
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	1,376		1,344		920	1,344
Income Tax Expense (Benefit)	431		463		284	463
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 1,376		$ 1,344		$ 920	$ 1,344