Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%	35.00%	35.00%
IPL's tax benefit riders	(11.00%)	(13.00%)	(10.60%)	(12.40%)
Effect of rate-making on property-related differences	(7.10%)	(8.60%)	(7.10%)	(6.70%)
Production tax credits	(6.70%)	(6.80%)	(6.60%)	(6.60%)
Other items, net	3.00%	0.70%	3.70%	2.90%
Overall income tax rate	13.20%	7.30%	14.40%	12.20%
IPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%	35.00%	35.00%
IPL's tax benefit riders	(30.00%)	(39.20%)	(28.20%)	(36.50%)
Effect of rate-making on property-related differences	(18.70%)	(22.40%)	(17.90%)	(18.40%)
Production tax credits	(8.70%)	(9.30%)	(8.20%)	(8.80%)
Other items, net	2.90%	2.20%	3.50%	3.20%
Overall income tax rate	(19.50%)	(33.70%)	(15.80%)	(25.50%)
WPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%	35.00%	35.00%
Effect of rate-making on property-related differences	(0.70%)	(0.80%)	(0.60%)	(0.70%)
Production tax credits	(6.00%)	(6.20%)	(6.20%)	(6.20%)
Other items, net	4.50%	0.00%	4.50%	3.00%
Overall income tax rate	32.80%	28.00%	32.70%	31.10%