Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Effective Tax Rate [Line Items]
Statutory federal income tax rate	21.00%	35.00%	21.00%	35.00%
State income taxes, net of federal benefits	6.50%	5.50%	7.10%	5.50%
Effect of rate-making on property-related differences	(6.70%)	(9.00%)	(7.20%)	(8.00%)
Production tax credits	(5.40%)	(5.90%)	(5.50%)	(5.90%)
IPL's tax benefit riders	(2.10%)	(7.80%)	(2.20%)	(7.80%)
Other items, net	(1.60%)	0.20%	(1.40%)	(2.40%)
Overall income tax rate	11.70%	18.00%	11.80%	16.40%
IPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	21.00%	35.00%	21.00%	35.00%
State income taxes, net of federal benefits	7.00%	6.50%	7.70%	6.40%
Effect of rate-making on property-related differences	(11.50%)	(18.00%)	(12.40%)	(18.00%)
Production tax credits	(5.30%)	(6.20%)	(5.30%)	(6.40%)
IPL's tax benefit riders	(4.30%)	(18.60%)	(4.50%)	(19.00%)
Other items, net	(2.80%)	0.00%	(1.50%)	(3.30%)
Overall income tax rate	4.10%	(1.30%)	5.00%	(5.30%)
WPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	21.00%	35.00%	21.00%	35.00%
State income taxes, net of federal benefits	6.20%	5.10%	6.20%	5.10%
Effect of rate-making on property-related differences	(2.70%)	(1.90%)	(2.50%)	(1.80%)
Production tax credits	(6.80%)	(7.10%)	(6.70%)	(7.00%)
Other items, net	(4.20%)	(0.60%)	(2.00%)	(0.60%)
Overall income tax rate	13.50%	30.50%	16.00%	30.70%