Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Effective Tax Rate [Line Items]
Statutory federal income tax rate	21.00%	35.00%
State income taxes, net of federal benefits	7.50%	5.40%
Effect of rate-making on property-related differences	(7.40%)	(7.50%)
Production tax credits	(5.50%)	(5.90%)
IPL's tax benefit riders	(2.20%)	(7.80%)
Other items, net	(1.40%)	(4.40%)
Overall income tax rate	12.00%	14.80%
IPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	21.00%	35.00%
State income taxes, net of federal benefits	8.50%	6.30%
Effect of rate-making on property-related differences	(13.50%)	(17.90%)
Production tax credits	(5.40%)	(6.60%)
IPL's tax benefit riders	(4.70%)	(19.40%)
Other items, net	0.00%	(7.60%)
Overall income tax rate	5.90%	(10.20%)
WPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	21.00%	35.00%
State income taxes, net of federal benefits	6.20%	5.10%
Effect of rate-making on property-related differences	(2.40%)	(1.70%)
Production tax credits	(6.70%)	(7.00%)
Other items, net	(0.30%)	(0.40%)
Overall income tax rate	17.80%	31.00%