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Commitments And Contingencies (Tables)
 12 Months Ended
Dec. 31, 2020
Long-term Purchase Commitment [Line Items]  
Other Purchase Commitments At December 31, 2020, the related minimum future commitments were as follows (in millions):
Alliant Energy20212022202320242025ThereafterTotal
Natural gas25217413710568185921
Coal702717———114
Other (a)6117118329129
$383$218$165$113$71$214$1,164
IPL20212022202320242025ThereafterTotal
Natural gas1308879683871474
Coal321613———61
Other (a)2554222765
$187$109$96$70$40$98$600
WPL20212022202320242025ThereafterTotal
Natural gas12286583730114447
Coal38114———53
Other (a)262111132
$186$99$63$38$31$115$532

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2020.
Schedule of Environmental Liabilities At December 31, 2020, 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, 2020, such amounts for WPL were not material.
Alliant EnergyIPL
Range of estimated future costs$11 -$28$8 -$22
Current and non-current environmental liabilities1512
IPL [Member]  
Long-term Purchase Commitment [Line Items]  
Other Purchase Commitments At December 31, 2020, the related minimum future commitments were as follows (in millions):
Alliant Energy20212022202320242025ThereafterTotal
Natural gas25217413710568185921
Coal702717———114
Other (a)6117118329129
$383$218$165$113$71$214$1,164
IPL20212022202320242025ThereafterTotal
Natural gas1308879683871474
Coal321613———61
Other (a)2554222765
$187$109$96$70$40$98$600
WPL20212022202320242025ThereafterTotal
Natural gas12286583730114447
Coal38114———53
Other (a)262111132
$186$99$63$38$31$115$532

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2020.
Schedule of Environmental Liabilities At December 31, 2020, 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, 2020, such amounts for WPL were not material.
Alliant EnergyIPL
Range of estimated future costs$11 -$28$8 -$22
Current and non-current environmental liabilities1512
WPL [Member]  
Long-term Purchase Commitment [Line Items]  
Other Purchase Commitments At December 31, 2020, the related minimum future commitments were as follows (in millions):
Alliant Energy20212022202320242025ThereafterTotal
Natural gas25217413710568185921
Coal702717———114
Other (a)6117118329129
$383$218$165$113$71$214$1,164
IPL20212022202320242025ThereafterTotal
Natural gas1308879683871474
Coal321613———61
Other (a)2554222765
$187$109$96$70$40$98$600
WPL20212022202320242025ThereafterTotal
Natural gas12286583730114447
Coal38114———53
Other (a)262111132
$186$99$63$38$31$115$532

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2020.