Benefit Plans (Assumptions Used To Measure Benefit Plans) (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	4.34%	3.66%	4.19%
Discount rate for net periodic cost	3.66%	4.19%	4.47%
Expected rate of return on plan assets	7.60%	7.60%	7.60%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan	5.04%	4.64%	3.17%
Pension Plans, Defined Benefit [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	4.35%	3.68%	4.22%
Discount rate for net periodic cost	3.68%	4.22%	4.50%
Expected rate of return on plan assets	7.60%	7.60%	7.60%
Rate of compensation increase	3.65%	3.65%	3.65%
Pension Plans, Defined Benefit [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	4.35%	3.69%	4.23%
Discount rate for net periodic cost	3.69%	4.23%	4.51%
Expected rate of return on plan assets	7.60%	7.60%	7.60%
Rate of compensation increase	3.65%	3.65%	3.65%
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	4.24%	3.53%	3.98%
Discount rate for net periodic cost	3.53%	3.98%	4.30%
Expected rate of return on plan assets	5.44%	5.80%	6.30%
Medical cost trend on covered charges, initial trend rate (end of year)	6.50%	6.75%	7.00%
Medical cost trend on covered charges, 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	4.23%	3.51%	3.95%
Discount rate for net periodic cost	3.51%	3.95%	4.28%
Expected rate of return on plan assets	5.60%	6.20%	6.60%
Medical cost trend on covered charges, initial trend rate (end of year)	6.50%	6.75%	7.00%
Medical cost trend on covered charges, 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	4.23%	3.51%	3.96%
Discount rate for net periodic cost	3.51%	3.96%	4.28%
Expected rate of return on plan assets	3.84%	3.50%	4.70%
Medical cost trend on covered charges, initial trend rate (end of year)	6.50%	6.75%	7.00%
Medical cost trend on covered charges, 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	3.65%	3.65%	3.65%
Maximum [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	4.50%	4.50%	4.50%