Regulatory Matters (Details) $ in Thousands					1 Months Ended		3 Months Ended	12 Months Ended
	Dec. 31, 2019 USD ($)	Oct. 31, 2018 USD ($)	Aug. 29, 2018 USD ($)	Apr. 26, 2017 USD ($)	Oct. 31, 2018 USD ($)	Mar. 31, 2016 USD ($)	Mar. 31, 2020 MW	Dec. 31, 2019 USD ($) MW	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jul. 24, 2019 USD ($)
Regulatory Matters [Line Items]
Equipment recovery approved amount								$ 17,400
Revenue requirement to be included in rate								28,400
Public Utlities, Approved Shareholder Incentives								7,500	$ 3,800	$ 0
Regulatory assets	$ 355,614							355,614	395,077
Regulatory Assets	393,012							393,012	423,476
Regulatory liabilities, current	52,654							52,654	51,024
Regulatory assets	37,398							$ 37,398	$ 28,399
Public Utilities, Approved Rate Increase (Decrease), Amount					$ 43,900	$ 30,800
Public Utilities, Approved Rate Increase (Decrease), Percentage					3.20%
Approved Rate Order Benefits to Customers	4,700
Wholesale Sales Margins, Percent Shared with Customers						50.00%
Benchmark for Wholesale Sales Margin						$ 6,300
TDSIC Eligible Cost Recovery Through Periodic Rate Adjustment Mechanism Plan, Percent								80.00%
TDSIC Planned Recoverable Costs Deferred For Future Recovery, Percent								20.00%
Periodic Rate Adjustment Mechanism Cap, Percent								2.00%
Preferred Resource Portfolio Coal-Fired Generation Retirement MW by 2023								630
Inventory Write-down								$ 6,200
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent								21.00%	21.00%	35.00%
Regulatory Liability, Noncurrent	846,430							$ 846,430	$ 870,255
Regulatory Liabilities	899,084							899,084	921,279
Undercollections of rate riders [Member]
Regulatory Matters [Line Items]
Regulatory assets	22,216							22,216	13,217
Amounts being recovered through base rates [Member]
Regulatory Matters [Line Items]
Regulatory assets	15,182							15,182	15,182
Pension Costs [Member]
Regulatory Matters [Line Items]
Regulatory assets	176,646							176,646	195,559
Deferred Income Tax Charge [Member]
Regulatory Matters [Line Items]
Regulatory Liability, Noncurrent	122,156							122,156	141,100
Deferred Project Costs [Member]
Regulatory Matters [Line Items]
Regulatory assets									88,052
Unamortized Carrying Charges And Certain Other Costs [Member]
Regulatory Matters [Line Items]
Regulatory assets	7,030							7,030	8,084
Loss on Reacquired Debt [Member]
Regulatory Matters [Line Items]
Regulatory assets	18,330							18,330	19,714
Environmental Restoration Costs [Member]
Regulatory Matters [Line Items]
Regulatory assets	78,021							78,021	81,204
Other Miscellaneous [Member]
Regulatory Matters [Line Items]
Regulatory assets	927							927	2,464
Deferred MISO Non-fuel Costs [Member]
Regulatory Matters [Line Items]
Regulatory assets	74,660							74,660
Indianapolis Power And Light Company
Regulatory Matters [Line Items]
Equipment recovery approved amount								17,400
Revenue requirement to be included in rate								28,400
Public Utlities, Approved Shareholder Incentives								7,500	3,800
Regulatory assets	355,614							355,614	395,077
Regulatory Assets	393,012							393,012	423,476
Regulatory liabilities, current	52,654							52,654	51,024
Regulatory assets	37,398							$ 37,398	$ 28,399
Public Utilities, Approved Rate Increase (Decrease), Amount					$ 43,900
Public Utilities, Approved Rate Increase (Decrease), Percentage					3.20%
Wholesale Sales Margins, Percent Shared with Customers						50.00%
Benchmark for Wholesale Sales Margin						$ 6,300
TDSIC Eligible Cost Recovery Through Periodic Rate Adjustment Mechanism Plan, Percent								80.00%
TDSIC Planned Recoverable Costs Deferred For Future Recovery, Percent								20.00%
Periodic Rate Adjustment Mechanism Cap, Percent								2.00%
TDSIC Plan Improvement Costs											$ 1,200,000
Preferred Resource Portfolio Coal-Fired Generation Retirement MW by 2023								630
Inventory Write-down								$ 6,200
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent								21.00%	21.00%	35.00%
Effective Income Tax Rate Reconciliation Tax Cuts and Jobs Act of 2017 Percent									21.00%
Regulatory Liability, Noncurrent	846,430							$ 846,430	$ 870,255
Regulatory Liabilities	899,084							899,084	921,279
Indianapolis Power And Light Company | Undercollections of rate riders [Member]
Regulatory Matters [Line Items]
Regulatory assets	22,216							22,216	13,217
Indianapolis Power And Light Company | Amounts being recovered through base rates [Member]
Regulatory Matters [Line Items]
Regulatory assets	15,182							15,182	15,182
Indianapolis Power And Light Company | Pension Costs [Member]
Regulatory Matters [Line Items]
Regulatory assets	176,646							176,646	195,559
Indianapolis Power And Light Company | Deferred Income Tax Charge [Member]
Regulatory Matters [Line Items]
Regulatory Liability, Noncurrent	122,156							122,156	141,100
Indianapolis Power And Light Company | Deferred Project Costs [Member]
Regulatory Matters [Line Items]
Regulatory assets									88,052
Indianapolis Power And Light Company | Unamortized Carrying Charges And Certain Other Costs [Member]
Regulatory Matters [Line Items]
Regulatory assets	7,030							7,030	8,084
Indianapolis Power And Light Company | Loss on Reacquired Debt [Member]
Regulatory Matters [Line Items]
Regulatory assets	18,330							18,330	19,714
Indianapolis Power And Light Company | Environmental Restoration Costs [Member]
Regulatory Matters [Line Items]
Regulatory assets	78,021							78,021	81,204
Indianapolis Power And Light Company | Other Miscellaneous [Member]
Regulatory Matters [Line Items]
Regulatory assets	927							927	2,464
Indianapolis Power And Light Company | Deferred MISO Non-fuel Costs [Member]
Regulatory Matters [Line Items]
Regulatory assets	74,660							$ 74,660
Indianapolis Power And Light Company | Indiana [Member]
Regulatory Matters [Line Items]
Amount of electricity required to be purchased under purchase power agreement | MW								100
Indianapolis Power And Light Company | Minnesota [Member]
Regulatory Matters [Line Items]
Amount of electricity required to be purchased under purchase power agreement | MW								200
Indianapolis Power And Light Company | Solar Generated Electricity [Member]
Regulatory Matters [Line Items]
Amount of electricity required to be purchased under purchase power agreement | MW								95.9
Subsequent Event [Member] | Indianapolis Power And Light Company | Solar Generated Electricity [Member]
Regulatory Matters [Line Items]
Amount of electricity required to be purchased under purchase power agreement | MW							96.4
Rate Order total benefits to customers [Member]
Regulatory Matters [Line Items]
Approved Rate Order Benefits to Customers		$ 50,000
Rate Order total benefits to customers [Member] | Indianapolis Power And Light Company
Regulatory Matters [Line Items]
Approved Rate Order Benefits to Customers		50,000
Benchmark for annual wholesale margins [Member]
Regulatory Matters [Line Items]
Approved Rate Order Benefits to Customers		16,300
Benchmark for annual wholesale margins [Member] | Indianapolis Power And Light Company
Regulatory Matters [Line Items]
Approved Rate Order Benefits to Customers		16,300
Benchmark for annual capacity sales [Member]
Regulatory Matters [Line Items]
Approved Rate Order Benefits to Customers		11,300
Benchmark for annual capacity sales [Member] | Indianapolis Power And Light Company
Regulatory Matters [Line Items]
Approved Rate Order Benefits to Customers		11,300
Increase to Annual Depreciation Rate [Member]
Regulatory Matters [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		28,700
Increase to Annual Depreciation Rate [Member] | Indianapolis Power And Light Company
Regulatory Matters [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		$ 28,700
ECCRA revenue requirement [Member]
Regulatory Matters [Line Items]
Approved Rate Order Benefits to Customers								$ 50,000
ECCRA revenue requirement [Member] | Indianapolis Power And Light Company
Regulatory Matters [Line Items]
Approved Rate Order Benefits to Customers								50,000
Federal Tax Act impact Phase 1 [Member]
Regulatory Matters [Line Items]
ECCRA rate adjustment mechanism			$ 9,500
Federal Tax Act impact Phase 1 [Member] | Indianapolis Power And Light Company
Regulatory Matters [Line Items]
ECCRA rate adjustment mechanism			9,500
Federal Tax Act Impact Phase II [Member]
Regulatory Matters [Line Items]
ECCRA rate adjustment mechanism			14,300
Federal Tax Act Impact Phase II [Member] | Indianapolis Power And Light Company
Regulatory Matters [Line Items]
ECCRA rate adjustment mechanism			$ 14,300
NAAQs [Member]
Regulatory Matters [Line Items]
Percentage of approved qualifying costs to recover				80.00%
Public Utilities, approved capital cost for compliance projects				$ 29,000
NAAQs [Member] | Indianapolis Power And Light Company
Regulatory Matters [Line Items]
Percentage of approved qualifying costs to recover				80.00%
Public Utilities, approved capital cost for compliance projects				$ 29,000
CCR [Member]
Regulatory Matters [Line Items]
Percentage of approved qualifying costs to recover				80.00%
Public Utilities, approved capital cost for compliance projects				$ 47,000
CCR [Member] | Indianapolis Power And Light Company
Regulatory Matters [Line Items]
Percentage of approved qualifying costs to recover				80.00%
Public Utilities, approved capital cost for compliance projects				$ 47,000
Overcollection and other credits passed to customers through rate riders [Member]
Regulatory Matters [Line Items]
Regulatory liabilities, current	51,790							51,790	47,925
Overcollection and other credits passed to customers through rate riders [Member] | Indianapolis Power And Light Company
Regulatory Matters [Line Items]
Regulatory liabilities, current	51,790							51,790	47,925
Unamortized Investment Tax Credit [Member]
Regulatory Matters [Line Items]
Regulatory Liability, Noncurrent	3,337							3,337	21,341
Unamortized Investment Tax Credit [Member] | Indianapolis Power And Light Company
Regulatory Matters [Line Items]
Regulatory Liability, Noncurrent	3,337							3,337	21,341
Financial Transmission Rights [Member]
Regulatory Matters [Line Items]
Regulatory liabilities, current	864							864	3,099
Financial Transmission Rights [Member] | Indianapolis Power And Light Company
Regulatory Matters [Line Items]
Regulatory liabilities, current	864							864	3,099
Asset Retirement Obligation Costs [Member]
Regulatory Matters [Line Items]
Regulatory Liability, Noncurrent	719,680							719,680	707,662
Asset Retirement Obligation Costs [Member] | Indianapolis Power And Light Company
Regulatory Matters [Line Items]
Regulatory Liability, Noncurrent	719,680							719,680	707,662
Deferred Income Tax Charge [Member]
Regulatory Matters [Line Items]
Regulatory Liability, Noncurrent									141,058
Deferred Income Tax Charge [Member] | Indianapolis Power And Light Company
Regulatory Matters [Line Items]
Regulatory Liability, Noncurrent									141,058
Other Regulatory Assets (Liabilities) [Member]
Regulatory Matters [Line Items]
Regulatory Liability, Noncurrent	1,257							1,257	194
Other Regulatory Assets (Liabilities) [Member] | Indianapolis Power And Light Company
Regulatory Matters [Line Items]
Regulatory Liability, Noncurrent	$ 1,257							$ 1,257	$ 194