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Asset Retirement Obligations
 6 Months Ended
Jun. 30, 2020
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 six months ended June 30, 2020 is as follows (in millions):
 
Alliant Energy
 
IPL
Balance, January 1

$196.3

 

$133.9

Revisions in estimated cash flows
0.9

 
—

Liabilities settled
(3.5
)
 
(2.8
)
Liabilities incurred (a)
27.6

 
27.6

Accretion expense
3.5

 
2.5

Balance, June 30

$224.8

 

$161.2


(a)
During the six months ended June 30, 2020, Alliant Energy and IPL recognized additional asset retirement obligations related to IPL’s newly constructed Whispering Willow North and Golden Plains wind sites. The increases in asset retirement obligations resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.
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 six months ended June 30, 2020 is as follows (in millions):
 
Alliant Energy
 
IPL
Balance, January 1

$196.3

 

$133.9

Revisions in estimated cash flows
0.9

 
—

Liabilities settled
(3.5
)
 
(2.8
)
Liabilities incurred (a)
27.6

 
27.6

Accretion expense
3.5

 
2.5

Balance, June 30

$224.8

 

$161.2


(a)
During the six months ended June 30, 2020, Alliant Energy and IPL recognized additional asset retirement obligations related to IPL’s newly constructed Whispering Willow North and Golden Plains wind sites. The increases in asset retirement obligations resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.