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Asset Retirement Obligations
 12 Months Ended
Dec. 31, 2019
Schedule of Asset Retirement Obligations [Line Items]  
Asset Retirement Obligations (AROs) ASSET RETIREMENT OBLIGATIONS
Recognized AROs relate to legal obligations for the removal, closure or dismantlement of several assets including, but not limited to, wind farms, ash ponds, active ash landfills, above ground storage tanks and solar generation. Recognized AROs also include legal obligations for the management and final disposition of asbestos and polychlorinated biphenyls. AROs are recorded in “Other current liabilities” and “Other liabilities” on the balance sheets. Refer to Note 2 for information regarding regulatory assets related to AROs. A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
 
Alliant Energy
 
IPL
 
WPL
 
2019
 
2018
 
2019
 
2018
 
2019
 
2018
Balance, January 1

$177.5

 

$184.5

 

$118.3

 

$134.1

 

$59.2

 

$50.4

Revisions in estimated cash flows
(5.5
)
 
(10.1
)
 
(6.7
)
 
(10.1
)
 
1.2

 
—

Liabilities settled
(8.8
)
 
(10.4
)
 
(8.4
)
 
(9.7
)
 
(0.4
)
 
(0.7
)
Liabilities incurred (a)
26.2

 
7.3

 
26.2

 
—

 
—

 
7.3

Accretion expense
6.9

 
6.2

 
4.5

 
4.0

 
2.4

 
2.2

Balance, December 31

$196.3

 

$177.5

 

$133.9

 

$118.3

 

$62.4

 

$59.2


(a)
In 2019, Alliant Energy and IPL recognized additional AROs related to IPL’s newly constructed Upland Prairie and English Farms wind sites. The increases in AROs resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.
IPL [Member]  
Schedule of Asset Retirement Obligations [Line Items]  
Asset Retirement Obligations (AROs) ASSET RETIREMENT OBLIGATIONS
Recognized AROs relate to legal obligations for the removal, closure or dismantlement of several assets including, but not limited to, wind farms, ash ponds, active ash landfills, above ground storage tanks and solar generation. Recognized AROs also include legal obligations for the management and final disposition of asbestos and polychlorinated biphenyls. AROs are recorded in “Other current liabilities” and “Other liabilities” on the balance sheets. Refer to Note 2 for information regarding regulatory assets related to AROs. A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
 
Alliant Energy
 
IPL
 
WPL
 
2019
 
2018
 
2019
 
2018
 
2019
 
2018
Balance, January 1

$177.5

 

$184.5

 

$118.3

 

$134.1

 

$59.2

 

$50.4

Revisions in estimated cash flows
(5.5
)
 
(10.1
)
 
(6.7
)
 
(10.1
)
 
1.2

 
—

Liabilities settled
(8.8
)
 
(10.4
)
 
(8.4
)
 
(9.7
)
 
(0.4
)
 
(0.7
)
Liabilities incurred (a)
26.2

 
7.3

 
26.2

 
—

 
—

 
7.3

Accretion expense
6.9

 
6.2

 
4.5

 
4.0

 
2.4

 
2.2

Balance, December 31

$196.3

 

$177.5

 

$133.9

 

$118.3

 

$62.4

 

$59.2


(a)
In 2019, Alliant Energy and IPL recognized additional AROs related to IPL’s newly constructed Upland Prairie and English Farms wind sites. The increases in AROs resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.
WPL [Member]  
Schedule of Asset Retirement Obligations [Line Items]  
Asset Retirement Obligations (AROs) ASSET RETIREMENT OBLIGATIONS
Recognized AROs relate to legal obligations for the removal, closure or dismantlement of several assets including, but not limited to, wind farms, ash ponds, active ash landfills, above ground storage tanks and solar generation. Recognized AROs also include legal obligations for the management and final disposition of asbestos and polychlorinated biphenyls. AROs are recorded in “Other current liabilities” and “Other liabilities” on the balance sheets. Refer to Note 2 for information regarding regulatory assets related to AROs. A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
 
Alliant Energy
 
IPL
 
WPL
 
2019
 
2018
 
2019
 
2018
 
2019
 
2018
Balance, January 1

$177.5

 

$184.5

 

$118.3

 

$134.1

 

$59.2

 

$50.4

Revisions in estimated cash flows
(5.5
)
 
(10.1
)
 
(6.7
)
 
(10.1
)
 
1.2

 
—

Liabilities settled
(8.8
)
 
(10.4
)
 
(8.4
)
 
(9.7
)
 
(0.4
)
 
(0.7
)
Liabilities incurred (a)
26.2

 
7.3

 
26.2

 
—

 
—

 
7.3

Accretion expense
6.9

 
6.2

 
4.5

 
4.0

 
2.4

 
2.2

Balance, December 31

$196.3

 

$177.5

 

$133.9

 

$118.3

 

$62.4

 

$59.2


(a)
In 2019, Alliant Energy and IPL recognized additional AROs related to IPL’s newly constructed Upland Prairie and English Farms wind sites. The increases in AROs resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.