Overview and Summary of Significant Accounting Policies (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($) generating_station MW	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 558,531	$ 518,761	$ 520,988	$ 546,476
Accumulated Other Comprehensive Income (Loss), Net of Tax	(13,826)	(56,063)	(43,420)	(19,750)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	30,050	(36,313)
Inventories	20,215		36,953
Cash and cash equivalents	$ 48,592		20,502
Number of customers	513,000
Number of generating stations | generating_station	4
Restricted Cash and Cash Equivalents	$ 5		6,120
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	48,597	55,491	26,622	48,552
Regulatory assets, current	60,395		58,553
Inventory, Net	80,610		95,506
Other Comprehensive Income (Loss), Net of Tax	29,594	(36,313)
Accounts Receivable, Allowance for Credit Loss, Current	1,966		3,155
Accounts Receivable, Credit Loss Expense (Reversal)	124
Accounts Receivable, Allowance for Credit Loss, Writeoff	(1,885)
Accounts Receivable, Allowance for Credit Loss, Recovery	572
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(13,826)	(56,063)	$ (43,420)	$ (19,750)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	30,050	(36,313)
Income Tax Expense (Benefit)	10,035	9,772
Income Tax Expense (Benefit)	10,035	9,772
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent	$ (456)	0
Indianapolis Power And Light Company [Member]
Debt Instrument [Line Items]
Electric generation capability for winter, megawatts | MW	3,705
Electric generation capability for summer, megawatts | MW	3,560
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	$ (13,826)	(56,063)
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	602	0
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest and Debt Expense	602	0
Income Tax Expense (Benefit)	(146)	0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	(456)	0
Income Tax Expense (Benefit)	(146)	0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ (456)	$ 0