Benefit Plans (Schedule Of Fair Value Of Pension Plan Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 738,947	$ 674,430	$ 647,573
Percentage by asset category	100.00%	100.00%
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 738,947	$ 674,430
Significant Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	0	0
Short-Term Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 115	$ 78
Percentage by asset category	0.00%	0.00%
Short-Term Investments [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 115	$ 78
U.S. Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 162,144	$ 329,877
Percentage by asset category	22.00%	49.00%
U.S. Equities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 162,144	$ 329,877
International Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 58,536	$ 58,833
Percentage by asset category	8.00%	9.00%
International Equities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 58,536	$ 58,833
Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 415,868	$ 230,926
Percentage by asset category	56.00%	34.00%
Fixed Income [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 415,868	$ 230,926
US Treasury Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 102,284	$ 54,716
Percentage by asset category	14.00%	8.00%
US Treasury Securities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 102,284	$ 54,716
Indianapolis Power And Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 738,947	$ 674,430		$ 647,573
Percentage by asset category	100.00%	100.00%
Indianapolis Power And Light Company [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 738,947	$ 674,430
Indianapolis Power And Light Company [Member] | Significant Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	0	0
Indianapolis Power And Light Company [Member] | Short-Term Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 115	$ 78
Percentage by asset category	0.00%	0.00%
Indianapolis Power And Light Company [Member] | Short-Term Investments [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 115	$ 78
Indianapolis Power And Light Company [Member] | U.S. Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 162,144	$ 329,877
Percentage by asset category	22.00%	49.00%
Indianapolis Power And Light Company [Member] | U.S. Equities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 162,144	$ 329,877
Indianapolis Power And Light Company [Member] | International Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 58,536	$ 58,833
Percentage by asset category	8.00%	9.00%
Indianapolis Power And Light Company [Member] | International Equities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 58,536	$ 58,833
Indianapolis Power And Light Company [Member] | Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 415,868	$ 230,926
Percentage by asset category	56.00%	34.00%
Indianapolis Power And Light Company [Member] | Fixed Income [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 415,868	$ 230,926
Indianapolis Power And Light Company [Member] | US Treasury Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 102,284	$ 54,716
Percentage by asset category	14.00%	8.00%
Indianapolis Power And Light Company [Member] | US Treasury Securities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of benefit plan assets	$ 102,284	$ 54,716