Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%
IPL's tax benefit riders	(8.70%)	(9.90%)
Effect of rate-making on property-related differences	(6.80%)	(6.10%)
Production tax credits	(6.30%)	(6.20%)
Other items, net	4.50%	4.30%
Overall income tax rate	17.70%	17.10%
IPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%
IPL's tax benefit riders	(20.70%)	(25.20%)
Effect of rate-making on property-related differences	(15.20%)	(14.60%)
Production tax credits	(6.70%)	(7.10%)
Other items, net	5.90%	4.80%
Overall income tax rate	(1.70%)	(7.10%)
WPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%
Effect of rate-making on property-related differences	(0.80%)	(0.60%)
Production tax credits	(6.50%)	(6.20%)
Other items, net	4.80%	4.40%
Overall income tax rate	32.50%	32.60%