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Asset Retirement Obligations (AROs)
 12 Months Ended
Dec. 31, 2012
Schedule of Asset Retirement Obligations [Line Items]  
Asset Retirement Obligations (AROs)
ASSET RETIREMENT OBLIGATIONS (AROs)
AROs recognized by Alliant Energy, IPL and WPL relate to legal obligations for the removal, closure or dismantlement of several assets including, but not limited to, wind projects, certain ash ponds, certain coal yards, active ash landfills and above ground storage tanks. Alliant Energy’s, IPL’s and WPL’s recognized AROs also include legal obligations for the management and final disposition of asbestos and PCB. Alliant Energy’s, IPL’s and WPL’s AROs are recorded in “Other long-term liabilities and deferred credits” on the Consolidated Balance Sheets. Refer to Note 1(b) 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
 
2012
 
2011
 
2012
 
2011
 
2012
 
2011
Balance, January 1

$91.1

 

$75.9

 

$56.2

 

$43.6

 

$34.9

 

$32.3

Revisions in estimated cash flows (a)
(6.4
)
 
7.8

 
(9.2
)
 
7.7

 
2.8

 
0.1

Liabilities settled
(3.4
)
 
(0.9
)
 
(3.3
)
 
(0.8
)
 
(0.1
)
 
(0.1
)
Liabilities incurred (b)
16.8

 
4.0

 
—

 
3.1

 
7.7

 
0.9

Accretion expense
3.4

 
4.3

 
1.8

 
2.6

 
1.6

 
1.7

Balance, December 31

$101.5

 

$91.1

 

$45.5

 

$56.2

 

$46.9

 

$34.9


(a)
In 2012 and 2011, IPL recorded revisions in estimated cash flows of ($8.2) million and $7.0 million, respectively, based on revised remediation timing and cost information for asbestos remediation at Sixth Street.
(b)
In 2012, Resources recorded AROs of $9.1 million related to its Franklin County wind project and WPL recorded AROs of $7.6 million related to Nelson Dewey.

In addition, certain of Alliant Energy’s, IPL’s and WPL’s AROs related to electric generating facility 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 facilities 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 (AROs)
AROs recognized by Alliant Energy, IPL and WPL relate to legal obligations for the removal, closure or dismantlement of several assets including, but not limited to, wind projects, certain ash ponds, certain coal yards, active ash landfills and above ground storage tanks. Alliant Energy’s, IPL’s and WPL’s recognized AROs also include legal obligations for the management and final disposition of asbestos and PCB. Alliant Energy’s, IPL’s and WPL’s AROs are recorded in “Other long-term liabilities and deferred credits” on the Consolidated Balance Sheets. Refer to Note 1(b) 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
 
2012
 
2011
 
2012
 
2011
 
2012
 
2011
Balance, January 1

$91.1

 

$75.9

 

$56.2

 

$43.6

 

$34.9

 

$32.3

Revisions in estimated cash flows (a)
(6.4
)
 
7.8

 
(9.2
)
 
7.7

 
2.8

 
0.1

Liabilities settled
(3.4
)
 
(0.9
)
 
(3.3
)
 
(0.8
)
 
(0.1
)
 
(0.1
)
Liabilities incurred (b)
16.8

 
4.0

 
—

 
3.1

 
7.7

 
0.9

Accretion expense
3.4

 
4.3

 
1.8

 
2.6

 
1.6

 
1.7

Balance, December 31

$101.5

 

$91.1

 

$45.5

 

$56.2

 

$46.9

 

$34.9


(a)
In 2012 and 2011, IPL recorded revisions in estimated cash flows of ($8.2) million and $7.0 million, respectively, based on revised remediation timing and cost information for asbestos remediation at Sixth Street.
(b)
In 2012, Resources recorded AROs of $9.1 million related to its Franklin County wind project and WPL recorded AROs of $7.6 million related to Nelson Dewey.

In addition, certain of Alliant Energy’s, IPL’s and WPL’s AROs related to electric generating facility 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 facilities 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 (AROs)
AROs recognized by Alliant Energy, IPL and WPL relate to legal obligations for the removal, closure or dismantlement of several assets including, but not limited to, wind projects, certain ash ponds, certain coal yards, active ash landfills and above ground storage tanks. Alliant Energy’s, IPL’s and WPL’s recognized AROs also include legal obligations for the management and final disposition of asbestos and PCB. Alliant Energy’s, IPL’s and WPL’s AROs are recorded in “Other long-term liabilities and deferred credits” on the Consolidated Balance Sheets. Refer to Note 1(b) 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
 
2012
 
2011
 
2012
 
2011
 
2012
 
2011
Balance, January 1

$91.1

 

$75.9

 

$56.2

 

$43.6

 

$34.9

 

$32.3

Revisions in estimated cash flows (a)
(6.4
)
 
7.8

 
(9.2
)
 
7.7

 
2.8

 
0.1

Liabilities settled
(3.4
)
 
(0.9
)
 
(3.3
)
 
(0.8
)
 
(0.1
)
 
(0.1
)
Liabilities incurred (b)
16.8

 
4.0

 
—

 
3.1

 
7.7

 
0.9

Accretion expense
3.4

 
4.3

 
1.8

 
2.6

 
1.6

 
1.7

Balance, December 31

$101.5

 

$91.1

 

$45.5

 

$56.2

 

$46.9

 

$34.9


(a)
In 2012 and 2011, IPL recorded revisions in estimated cash flows of ($8.2) million and $7.0 million, respectively, based on revised remediation timing and cost information for asbestos remediation at Sixth Street.
(b)
In 2012, Resources recorded AROs of $9.1 million related to its Franklin County wind project and WPL recorded AROs of $7.6 million related to Nelson Dewey.

In addition, certain of Alliant Energy’s, IPL’s and WPL’s AROs related to electric generating facility 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 facilities are being recovered in rates and are recorded in regulatory liabilities.