Benefit Plans (Narrative) (Details) $ in Thousands			3 Months Ended	12 Months Ended
	Jan. 01, 2020	Jan. 01, 2016	Mar. 31, 2018 USD ($)	Dec. 31, 2020	Dec. 31, 2019 USD ($) employee	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2013 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement			$ 1,200
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation					$ 782,795	$ 697,228
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Plan Assets					769,704	684,485
Noncurrent liabilities					13,091	12,743
Benefit obligation in excess of plan assets					(13,091)	(12,743)
Accumulated benefit obligation in excess of plan assets					1,888	2,651
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)					88,311	(62,303)
Net loss (gain) arising during period					4,472	(902)
Pension liability actuarial loss, change in discount rate					88,300
Amount included in regulatory assets and liabilities					167,750	183,306
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Plan Assets					$ 769,704	684,485
Expected return on plan assets					4.50%
Effect of 25 basis point increase in discount rate on pension expense					$ (1,200)
Effect of 25 basis point decrease in discount rate on pension expense					1,100
Employer contributions during quarter					$ 28	30,085	$ 7,200
Funded target liability (percent)					101.00%
Pension expense					$ 37,500	62,100	35,500
Service cost					7,412	8,450	7,344
Interest cost					27,343	25,220	25,305
Defined Benefit Plan, Benefit Obligation					$ 782,795	$ 697,228	$ 782,108
Pension Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of employees covered by the plan					76.00%
Benefit obligation in excess of plan assets					$ 12,000
Accumulated benefit obligation in excess of plan assets					$ 800
Discount rate		3.33%			4.36%	3.67%	4.29%
Expected return on plan assets					4.50%	5.45%	6.75%
Supplemental Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of plan participants | employee					22
Benefit obligation in excess of plan assets					$ 1,100
Accumulated benefit obligation in excess of plan assets					$ 1,100
Discount rate		3.05%			4.24%	3.60%	4.00%
Expected return on plan assets					4.50%	5.45%	6.75%
Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of plan participants, active | employee					147
Number of plan participants, retired | employee					17
Indianapolis Power And Light Company
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement			$ 1,200
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation					$ 782,795	$ 697,228
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Plan Assets					769,704	684,485
Noncurrent liabilities					13,091	12,743
Benefit obligation in excess of plan assets					(13,091)	(12,743)
Accumulated benefit obligation in excess of plan assets					1,888	2,651
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)					88,311	(62,303)
Net loss (gain) arising during period					4,472	(902)
Pension liability actuarial loss					92,800
Amount included in regulatory assets and liabilities					$ 167,750	183,306
Minimum percentage of unrecognized net loss over benefit obligation or assets in order to be amortized					10.00%
Amortization period of unrecognized loss					10 years 11 months 15 days
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Plan Assets					$ 769,704	684,485
Unfunded status of plan					$ 13,100
Expected return on plan assets					4.50%
Effect of 25 basis point increase in discount rate on pension expense					$ (1,200)
Effect of 25 basis point decrease in discount rate on pension expense					1,100
Employer contributions during quarter					$ 28	30,085	$ 7,200
Funded target liability (percent)					101.00%
Normal service cost					$ 7,600
Plan expenses					2,300
Pension expense					37,500	62,100	35,500
Service cost					7,412	8,450	7,344
Interest cost					27,343	25,220	$ 25,305
Defined Benefit Plan, Benefit Obligation					$ 782,795	$ 697,228		$ 782,108
Indianapolis Power And Light Company | Pension Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of employees covered by the plan					76.00%
Benefit obligation in excess of plan assets					$ (12,000)
Accumulated benefit obligation in excess of plan assets					$ 800
Discount rate		3.33%			4.36%	3.67%	4.29%
Expected return on plan assets					4.50%	5.45%	6.75%
Indianapolis Power And Light Company | Supplemental Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of plan participants | employee					22
Benefit obligation in excess of plan assets					$ (1,100)
Accumulated benefit obligation in excess of plan assets					$ 1,100
Discount rate		3.05%			4.24%	3.60%	4.00%
Expected return on plan assets					4.50%	5.45%	6.75%
Indianapolis Power And Light Company | Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of plan participants, active | employee					147
Number of plan participants, retired | employee					17
Indianapolis Power And Light Company | Postretirement Health Coverage [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation					$ 6,400	$ 6,700
Subsequent Event [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	5.05%
Subsequent Event [Member] | Indianapolis Power And Light Company
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	5.05%
Thrift Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of employees covered by the plan					82.00%
Defined contripution plan contributions					$ 3,300	3,300	$ 3,400
Thrift Plan [Member] | Indianapolis Power And Light Company
Defined Benefit Plan Disclosure [Line Items]
Percentage of employees covered by the plan					82.00%
Defined contripution plan contributions					$ 3,300	3,300	3,400
Retirement Savings Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of employees covered by the plan					18.00%
Percentage of employee's base compensation matched					5.00%
Defined Contribution, Employer Matching Contribution, Non-discretionary, percent of match					4.00%
Defined contripution plan contributions					$ 1,600	1,700	1,800
Retirement Savings Plan [Member] | Indianapolis Power And Light Company
Defined Benefit Plan Disclosure [Line Items]
Percentage of employees covered by the plan					18.00%
Percentage of employee's base compensation matched					5.00%
Defined Contribution, Employer Matching Contribution, Non-discretionary, percent of match					4.00%
Defined contripution plan contributions					$ 1,600	$ 1,700	$ 1,800
Union Employees [Member] | Thrift Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of employees covered by the plan					6.00%
Union Employees [Member] | Thrift Plan [Member] | Indianapolis Power And Light Company
Defined Benefit Plan Disclosure [Line Items]
Percentage of employees covered by the plan					6.00%
Expected Increase or Decrease in Discount Rate [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Effect of Twenty Five Basis Point Increase Or Decrease In Discount Rate On Pension Expense				2500.00%
Expected Increase or Decrease in Discount Rate [Member] | Indianapolis Power And Light Company
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Effect of Twenty Five Basis Point Increase Or Decrease In Discount Rate On Pension Expense				2500.00%