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Asset Retirement Obligations
 12 Months Ended
Dec. 31, 2017
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, ash ponds, wind farms, active ash landfills, solar generation and above ground storage tanks. Recognized AROs also include legal obligations for the management and final disposition of asbestos, polychlorinated biphenyls and lead-based paint. 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
 
2017
 
2016
 
2017
 
2016
 
2017
 
2016
Balance, January 1

$195.7

 

$214.0

 

$124.7

 

$132.9

 

$61.4

 

$71.9

Revisions in estimated cash flows
4.3

 
(13.3
)
 
7.0

 
(5.8
)
 
(2.7
)
 
(7.5
)
Liabilities settled
(23.5
)
 
(14.0
)
 
(13.1
)
 
(6.8
)
 
(10.4
)
 
(7.2
)
Liabilities incurred
2.0

 
2.6

 
11.7

 
0.7

 
—

 
1.9

Accretion expense
6.0

 
6.4

 
3.8

 
3.7

 
2.1

 
2.3

Balance, December 31

$184.5

 

$195.7

 

$134.1

 

$124.7

 

$50.4

 

$61.4


In addition, certain AROs related to EGU assets have not been recognized. Due to an indeterminate remediation date, the fair values of the AROs for these assets cannot be currently estimated. A liability for these AROs will be recorded when fair value is determinable. Removal costs of these EGUs are being recovered in rates and are recorded in regulatory liabilities.
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, ash ponds, wind farms, active ash landfills, solar generation and above ground storage tanks. Recognized AROs also include legal obligations for the management and final disposition of asbestos, polychlorinated biphenyls and lead-based paint. 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
 
2017
 
2016
 
2017
 
2016
 
2017
 
2016
Balance, January 1

$195.7

 

$214.0

 

$124.7

 

$132.9

 

$61.4

 

$71.9

Revisions in estimated cash flows
4.3

 
(13.3
)
 
7.0

 
(5.8
)
 
(2.7
)
 
(7.5
)
Liabilities settled
(23.5
)
 
(14.0
)
 
(13.1
)
 
(6.8
)
 
(10.4
)
 
(7.2
)
Liabilities incurred
2.0

 
2.6

 
11.7

 
0.7

 
—

 
1.9

Accretion expense
6.0

 
6.4

 
3.8

 
3.7

 
2.1

 
2.3

Balance, December 31

$184.5

 

$195.7

 

$134.1

 

$124.7

 

$50.4

 

$61.4


In addition, certain AROs related to EGU assets have not been recognized. Due to an indeterminate remediation date, the fair values of the AROs for these assets cannot be currently estimated. A liability for these AROs will be recorded when fair value is determinable. Removal costs of these EGUs are being recovered in rates and are recorded in regulatory liabilities.
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, ash ponds, wind farms, active ash landfills, solar generation and above ground storage tanks. Recognized AROs also include legal obligations for the management and final disposition of asbestos, polychlorinated biphenyls and lead-based paint. 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
 
2017
 
2016
 
2017
 
2016
 
2017
 
2016
Balance, January 1

$195.7

 

$214.0

 

$124.7

 

$132.9

 

$61.4

 

$71.9

Revisions in estimated cash flows
4.3

 
(13.3
)
 
7.0

 
(5.8
)
 
(2.7
)
 
(7.5
)
Liabilities settled
(23.5
)
 
(14.0
)
 
(13.1
)
 
(6.8
)
 
(10.4
)
 
(7.2
)
Liabilities incurred
2.0

 
2.6

 
11.7

 
0.7

 
—

 
1.9

Accretion expense
6.0

 
6.4

 
3.8

 
3.7

 
2.1

 
2.3

Balance, December 31

$184.5

 

$195.7

 

$134.1

 

$124.7

 

$50.4

 

$61.4


In addition, certain AROs related to EGU assets have not been recognized. Due to an indeterminate remediation date, the fair values of the AROs for these assets cannot be currently estimated. A liability for these AROs will be recorded when fair value is determinable. Removal costs of these EGUs are being recovered in rates and are recorded in regulatory liabilities.