Benefit Plans (Assumptions Used To Measure Benefit Plans) (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	2.57%	3.48%	4.34%
Discount rate for net periodic cost	3.48%	4.34%	3.66%
Expected rate of return on plan assets	7.10%	7.60%	7.60%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan	4.76%	5.52%	5.04%
Pension Plans, Defined Benefit [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	2.61%	3.51%	4.35%
Discount rate for net periodic cost	3.51%	4.35%	3.68%
Expected rate of return on plan assets	7.10%	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	2.64%	3.50%	4.35%
Discount rate for net periodic cost	3.50%	4.35%	3.69%
Expected rate of return on plan assets	7.10%	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	2.31%	3.40%	4.24%
Discount rate for net periodic cost	3.40%	4.24%	3.53%
Expected rate of return on plan assets	4.50%	5.44%	5.44%
Other Postretirement Benefits Plans [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	2.28%	3.39%	4.23%
Discount rate for net periodic cost	3.39%	4.23%	3.51%
Expected rate of return on plan assets	4.50%	5.60%	5.60%
Other Postretirement Benefits Plans [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	2.27%	3.39%	4.23%
Discount rate for net periodic cost	3.39%	4.23%	3.51%
Expected rate of return on plan assets	3.28%	3.81%	3.84%
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%