Overview and Summary of Significant Accounting Policies (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($) generating_station MW	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	May 31, 2021
Debt Instrument [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 1,124,972		$ 1,129,722
Asset Retirement Obligation, Revision of Estimate	8,525	$ 0
Asset Retirement Obligation, Accretion Expense	2,737	2,639
Accumulated Other Comprehensive Income (Loss), Net of Tax	36,680		29,294	$ 22,269
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	6,626	(8,532)
Inventories	69,185		77,198
Cash and cash equivalents	$ 435,217	28,579	28,579
Number of customers	524,000
Number of generating stations | generating_station	4
Restricted Cash and Cash Equivalents	$ 5	5
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	435,222	167,457	28,584	201,553
Regulatory assets, current	67,820		66,392
Inventory, Net	137,005		143,590
Other Comprehensive Income (Loss), Net of Tax	7,386	(7,174)
Accounts Receivable, Allowance for Credit Loss, Current	3,765	1,063	2,283	1,117
Accounts Receivable, Credit Loss Expense (Reversal)	1,022	983
Accounts Receivable, Allowance for Credit Loss, Writeoff	(159)	(1,522)
Accounts Receivable, Allowance for Credit Loss, Recovery	619	485
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	36,680		29,294	22,269
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(8,532)
Income Tax Expense (Benefit)	3,909	5,214
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	17,162	19,115
Capitalized Computer Software, Amortization	6,940	2,987
Income Tax Expense (Benefit)	3,909	5,214
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	17,162	19,115
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent	$ 760	1,358
Petersburg Unit 1 retired MW					230
Petersburg Unit 2 Planned Retirement MW in 2023	415
Preferred Resource Portfolio Coal-Fired Generation Retirement MW by 2023	630
Asset Retirement Obligation	$ 267,872	218,412	249,930	$ 218,729
Asset Retirement Obligation, Liabilities Incurred	7,778	69
Asset Retirement Obligation, Liabilities Settled	(1,098)	(3,025)
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain (Loss), Net	(1,523)	0
Allowance for Funds Used During Construction, Capitalized Interest	5,276	2,985
Allowance for Funds Used During Construction, Equity Portion	831	1,570
Capitalized Computer Software, Amortization	6,940	2,987
Capitalized Computer Software, Gross	265,224		261,872
Project development intangible assets	83,940		84,097
Emissions Allowance	797		797
Capitalized Computer Software, Accumulated Amortization	116,963		111,110
Intangible Assets, Net (Including Goodwill)	$ 232,998		$ 235,656
Petersburg Energy Center Project MW	250
Petersburg Energy Storage Project MW	45
Petersburg Energy Storage Project MwH	180
Hardy Hills Solar Project MW	195
Hoosier Wind Project MW	106
Pike Co BESS Project MW	200
Pike Co BESS Project MwH	800
Indianapolis Power And Light Company [Member]
Debt Instrument [Line Items]
Electric generation capability for winter, megawatts | MW	3,070
Electric generation capability for summer, megawatts | MW	2,925
Aes U.S. Investments [Member]
Debt Instrument [Line Items]
Ownership percentage by parent (percent)	82.35%
CDPQ [Member]
Debt Instrument [Line Items]
Ownership percentage by parent (percent)	17.65%
Ownership interest in parent company (percent)	15.00%
AES U.S. Holdings, LLC [Member]
Debt Instrument [Line Items]
Ownership interest in parent company (percent)	85.00%
Harding Street [Member]
Debt Instrument [Line Items]
Amount of New Operation for Battery Storage Unit, megawatts | MW	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	$ 36,680	15,095
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	(1,012)	(1,807)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest and Debt Expense	(1,012)	(1,807)
Income Tax Expense (Benefit)	252	449
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	760	1,358
Income Tax Expense (Benefit)	252	449
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 760	$ 1,358