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Commitments And Contingencies (Tables)
 12 Months Ended
Dec. 31, 2021
Long-term Purchase Commitment [Line Items]  
Other Purchase Commitments At December 31, 2021, the related minimum future commitments were as follows (in millions):
Alliant Energy20222023202420252026ThereafterTotal
Natural gas$307$196$144$102$88$175$1,012
Coal6346253——137
Other (a)821485225136
$452$256$177$110$90$200$1,285
IPL20222023202420252026ThereafterTotal
Natural gas$148$108$84$52$42$65$499
Coal3227173——79
Other (a)3442222367
$214$139$103$57$44$88$645
WPL20222023202420252026ThereafterTotal
Natural gas$159$88$60$50$46$110$513
Coal31198———58
Other (a)331111—37
$223$108$69$51$47$110$608

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2021.
Schedule of Environmental Liabilities At December 31, 2021, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions). At December 31, 2021, such amounts for WPL were not material.
Alliant EnergyIPL
Range of estimated future costs$8 -$24$6 -$18
Current and non-current environmental liabilities118
IPL [Member]  
Long-term Purchase Commitment [Line Items]  
Other Purchase Commitments At December 31, 2021, the related minimum future commitments were as follows (in millions):
Alliant Energy20222023202420252026ThereafterTotal
Natural gas$307$196$144$102$88$175$1,012
Coal6346253——137
Other (a)821485225136
$452$256$177$110$90$200$1,285
IPL20222023202420252026ThereafterTotal
Natural gas$148$108$84$52$42$65$499
Coal3227173——79
Other (a)3442222367
$214$139$103$57$44$88$645
WPL20222023202420252026ThereafterTotal
Natural gas$159$88$60$50$46$110$513
Coal31198———58
Other (a)331111—37
$223$108$69$51$47$110$608

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2021.
Schedule of Environmental Liabilities At December 31, 2021, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions). At December 31, 2021, such amounts for WPL were not material.
Alliant EnergyIPL
Range of estimated future costs$8 -$24$6 -$18
Current and non-current environmental liabilities118
WPL [Member]  
Long-term Purchase Commitment [Line Items]  
Other Purchase Commitments At December 31, 2021, the related minimum future commitments were as follows (in millions):
Alliant Energy20222023202420252026ThereafterTotal
Natural gas$307$196$144$102$88$175$1,012
Coal6346253——137
Other (a)821485225136
$452$256$177$110$90$200$1,285
IPL20222023202420252026ThereafterTotal
Natural gas$148$108$84$52$42$65$499
Coal3227173——79
Other (a)3442222367
$214$139$103$57$44$88$645
WPL20222023202420252026ThereafterTotal
Natural gas$159$88$60$50$46$110$513
Coal31198———58
Other (a)331111—37
$223$108$69$51$47$110$608

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2021.