Benefit Plans (Assumptions Used To Measure Benefit Plans ) (Details)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	5.20%
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	4.86%	5.56%	5.80%
Discount rate for net periodic cost	5.56%	5.80%	6.15%
Expected rate of return on plan assets	7.90%	8.00%	8.25%
Defined Benefit Pension Plans [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	4.95%	5.70%	5.80%
Discount rate for net periodic cost	5.70%	5.80%	6.15%
Expected rate of return on plan assets	7.90%	8.00%	8.25%
Rate of compensation increase	3.50%	3.50%	3.50%
Defined Benefit Pension Plans [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	4.95%	5.70%	5.80%
Discount rate for net periodic cost	5.70%	5.80%	6.15%
Expected rate of return on plan assets	7.90%	8.00%	8.25%
Rate of compensation increase	3.50%	3.50%	3.50%
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	4.60%	5.25%	5.55%
Discount rate for net periodic cost	5.25%	5.55%	6.15%
Expected rate of return on plan assets	7.00%	6.90%	8.25%
Rate of compensation increase	3.50%	3.50%	3.50%
Initial trend rate (end of year)	8.00%	7.00%	7.50%
Ultimate trend rate	5.00%	5.00%	5.00%
Other Postretirement Benefits Plans [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	4.60%	5.25%	5.55%
Discount rate for net periodic cost	5.25%	5.55%	6.15%
Expected rate of return on plan assets	7.30%	7.10%	8.25%
Rate of compensation increase	3.50%	3.50%	3.50%
Initial trend rate (end of year)	8.00%	7.00%	7.50%
Ultimate trend rate	5.00%	5.00%	5.00%
Other Postretirement Benefits Plans [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	4.60%	5.25%	5.55%
Discount rate for net periodic cost	5.25%	5.55%	6.15%
Expected rate of return on plan assets	6.30%	6.30%	8.25%
Rate of compensation increase	3.50%	3.50%	3.50%
Initial trend rate (end of year)	8.00%	7.00%	7.50%
Ultimate trend rate	5.00%	5.00%	5.00%
Minimum [Member] | Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	3.50%	3.50%	3.50%
Maximum [Member] | Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	4.50%	4.50%	4.50%