Benefit Plans (Narrative) (Details) $ in Thousands			12 Months Ended
	Jan. 01, 2018	Jan. 01, 2016	Dec. 31, 2017 USD ($) employee	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2013 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Noncurrent liabilities			$ 43,161	$ 57,395
Benefit obligation in excess of plan assets			43,161	57,395
Accumulated benefit obligation in excess of plan assets			30,731	46,471
Net loss (gain) arising during period			4,101	7,690
Amount included in regulatory assets and liabilities			193,807	203,047
Benefit obligation			782,108	731,825
Plan assets			$ 738,947	674,430
Expected return on plan assets			6.75%
Effect of 25 basis point increase in discount rate on pension expense			$ (1,400)
Effect of 25 basis point decrease in discount rate on pension expense			1,400
Amortization of net losses from regulatory assets			11,600
Amortization of net periodic benefit cost from regulatory assets			4,000
Employer contributions during quarter			7,212	15,950	$ 25,200
Pension expense			35,500	34,600	35,700
Service cost			7,344	7,018	8,314
Interest cost			25,305	25,815	29,638
Defined Benefit Plan, Benefit Obligation			$ 782,108	$ 731,825	$ 723,887
Pension Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of employees covered by the plan			78.00%
Benefit obligation in excess of plan assets			$ (42,400)
Accumulated benefit obligation in excess of plan assets			$ 29,900
Discount rate		3.67%	4.29%	4.42%	4.06%
Expected return on plan assets			6.75%	6.75%	6.75%
Amortization of net losses from regulatory assets			$ 11,400
Amortization of net periodic benefit cost from regulatory assets			$ 4,000
Supplemental Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of plan participants | employee			22
Benefit obligation in excess of plan assets			$ (800)
Accumulated benefit obligation in excess of plan assets			$ 800
Discount rate		3.60%	4.00%	4.19%	3.82%
Expected return on plan assets			6.75%	6.75%	6.75%
Amortization of net losses from regulatory assets			$ 200
Amortization of net periodic benefit cost from regulatory assets			$ 0
Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of plan participants, active | employee			163
Number of plan participants, retired | employee			6
Indianapolis Power And Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Noncurrent liabilities			$ 43,161	$ 57,395
Benefit obligation in excess of plan assets			43,161	57,395
Accumulated benefit obligation in excess of plan assets			30,731	46,471
Net loss (gain) arising during period			4,101	7,690
Pension liability actuarial loss			48,400
Pension liability actuarial loss, change in discount rate			52,500
Amount included in regulatory assets and liabilities			$ 193,807	203,047
Minimum percentage of unrecognized net loss over benefit obligation or assets in order to be amortized			10.00%
Amortization period of unrecognized loss			9 years 9 months 58 days
Benefit obligation			$ 782,108	731,825
Plan assets			738,947	674,430
Unfunded status of plan			$ (43,200)
Expected return on plan assets			6.75%
Effect of 25 basis point increase in discount rate on pension expense			$ (1,400)
Effect of 25 basis point decrease in discount rate on pension expense			1,400
Amortization of net losses from regulatory assets			11,600
Amortization of net periodic benefit cost from regulatory assets			4,000
Employer contributions during quarter			$ 7,212	15,950	$ 25,200
Funded target liability (percent)			110.00%
Normal service cost			$ 7,300
Plan expenses			1,700
Required funding in next fiscal year			30,000
Pension expense			35,500	34,600	35,700
Service cost			7,344	7,018	8,314
Interest cost			25,305	25,815	$ 29,638
Defined Benefit Plan, Benefit Obligation			$ 782,108	$ 731,825		$ 723,887
Indianapolis Power And Light Company [Member] | Pension Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of employees covered by the plan			78.00%
Benefit obligation in excess of plan assets			$ 42,400
Accumulated benefit obligation in excess of plan assets			$ 29,900
Discount rate		3.67%	4.29%	4.42%	4.06%
Expected return on plan assets			6.75%	6.75%	6.75%
Amortization of net losses from regulatory assets			$ 11,400
Amortization of net periodic benefit cost from regulatory assets			$ 4,000
Indianapolis Power And Light Company [Member] | Supplemental Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of plan participants | employee			22
Benefit obligation in excess of plan assets			$ 800
Accumulated benefit obligation in excess of plan assets			$ 800
Discount rate		3.60%	4.00%	4.19%	3.82%
Expected return on plan assets			6.75%	6.75%	6.75%
Amortization of net losses from regulatory assets			$ 200
Amortization of net periodic benefit cost from regulatory assets			$ 0
Indianapolis Power And Light Company [Member] | Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of plan participants, active | employee			163
Number of plan participants, retired | employee			6
Indianapolis Power And Light Company [Member] | Postretirement Health Coverage [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation			$ 7,000	$ 6,800
Subsequent Event [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	5.45%
Subsequent Event [Member] | Indianapolis Power And Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	5.45%
Thrift Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of employees covered by the plan			85.00%
Defined contripution plan contributions			$ 3,400	3,100	$ 3,100
Thrift Plan [Member] | Indianapolis Power And Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of employees covered by the plan			85.00%
Defined contripution plan contributions			$ 3,400	3,100	3,100
Retirement Savings Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of employees covered by the plan			15.00%
Percentage of employee's base compensation matched			5.00%
Defined contripution plan contributions			$ 1,800	1,000	300
Retirement Savings Plan [Member] | Indianapolis Power And Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of employees covered by the plan			15.00%
Percentage of employee's base compensation matched			5.00%
Defined contripution plan contributions			$ 1,800	$ 1,000	$ 300
Union Employees [Member] | Thrift Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of employees covered by the plan			7.00%
Union Employees [Member] | Thrift Plan [Member] | Indianapolis Power And Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of employees covered by the plan			7.00%