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Asset Retirement Obligations
 9 Months Ended
Sep. 30, 2021
Asset Retirement Obligations [Line Items]  
Asset Retirement Obligations ASSET RETIREMENT OBLIGATIONS
A reconciliation of the changes in asset retirement obligations associated with long-lived assets for the nine months ended September 30, 2021 is as follows (in millions):
Alliant EnergyIPL
Balance, January 1$251$177
Revisions in estimated cash flows 3732
Liabilities settled(10)(8)
Liabilities incurred1—
Accretion expense64
Balance, September 30
$285$205
IPL [Member]  
Asset Retirement Obligations [Line Items]  
Asset Retirement Obligations ASSET RETIREMENT OBLIGATIONS
A reconciliation of the changes in asset retirement obligations associated with long-lived assets for the nine months ended September 30, 2021 is as follows (in millions):
Alliant EnergyIPL
Balance, January 1$251$177
Revisions in estimated cash flows 3732
Liabilities settled(10)(8)
Liabilities incurred1—
Accretion expense64
Balance, September 30
$285$205