Benefit Plans (Assumptions Used To Measure Benefit Plans) (Details)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations		5.20%
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	4.11%	4.86%	5.56%
Discount rate for net periodic cost	4.86%	5.56%	5.80%
Expected rate of return on plan assets	7.90%	7.90%	8.00%
Pension Plans, Defined Benefit [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	4.20%	4.95%	5.70%
Discount rate for net periodic cost	4.95%	5.70%	5.80%
Expected rate of return on plan assets	7.90%	7.90%	8.00%
Rate of compensation increase	3.50%	3.50%	3.50%
Pension Plans, Defined Benefit [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	4.20%	4.95%	5.70%
Discount rate for net periodic cost	4.95%	5.70%	5.80%
Expected rate of return on plan assets	7.90%	7.90%	8.00%
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	3.82%	4.60%	5.25%
Discount rate for net periodic cost	4.60%	5.25%	5.55%
Expected rate of return on plan assets	7.50%	7.00%	6.90%
Rate of compensation increase	3.50%	3.50%	3.50%
Initial trend rate (end of year)	7.50%	8.00%	7.00%
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	3.76%	4.60%	5.25%
Discount rate for net periodic cost	4.60%	5.25%	5.55%
Expected rate of return on plan assets	7.40%	7.30%	7.10%
Rate of compensation increase	3.50%	3.50%	3.50%
Initial trend rate (end of year)	7.50%	8.00%	7.00%
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	3.81%	4.60%	5.25%
Discount rate for net periodic cost	4.60%	5.25%	5.55%
Expected rate of return on plan assets	7.00%	6.30%	6.30%
Rate of compensation increase	3.50%	3.50%	3.50%
Initial trend rate (end of year)	7.50%	8.00%	7.00%
Ultimate trend rate	5.00%	5.00%	5.00%
Minimum [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	3.50%	3.50%	3.50%
Maximum [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	4.50%	4.50%	4.50%