Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%
IPL's tax benefit riders	(7.80%)	(8.70%)
Effect of rate-making on property-related differences	(7.50%)	(6.80%)
Production tax credits	(5.90%)	(6.30%)
Other items, net	1.00%	4.50%
Overall income tax rate	14.80%	17.70%
IPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%
IPL's tax benefit riders	(19.40%)	(20.70%)
Effect of rate-making on property-related differences	(17.90%)	(15.20%)
Production tax credits	(6.60%)	(6.70%)
Other items, net	(1.30%)	5.90%
Overall income tax rate	(10.20%)	(1.70%)
WPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%
Effect of rate-making on property-related differences	(1.70%)	(0.80%)
Production tax credits	(7.00%)	(6.50%)
Other items, net	4.70%	4.80%
Overall income tax rate	31.00%	32.50%