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Asset Retirement Obligations (AROs) (Tables)
 12 Months Ended
Dec. 31, 2013
Schedule of Asset Retirement Obligations [Line Items]  
Reconciliation Of Changes In Asset Retirement Obligations (AROs)
A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
 
Alliant Energy
 
IPL
 
WPL
 
2013
 
2012
 
2013
 
2012
 
2013
 
2012
Balance, January 1

$101.5

 

$91.1

 

$45.5

 

$56.2

 

$46.9

 

$34.9

Revisions in estimated cash flows (a)
5.6

 
(6.4
)
 
0.1

 
(9.2
)
 
5.5

 
2.8

Liabilities settled
(2.3
)
 
(3.4
)
 
(0.6
)
 
(3.3
)
 
(1.7
)
 
(0.1
)
Liabilities incurred (b)
1.2

 
16.8

 
1.2

 
—

 
—

 
7.7

Accretion expense
3.7

 
3.4

 
1.7

 
1.8

 
1.7

 
1.6

Balance, December 31

$109.7

 

$101.5

 

$47.9

 

$45.5

 

$52.4

 

$46.9


(a)
In 2012, IPL recorded revisions in estimated cash flows of ($8.2) million 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.
IPL [Member]
  
Schedule of Asset Retirement Obligations [Line Items]  
Reconciliation Of Changes In Asset Retirement Obligations (AROs)
A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
 
Alliant Energy
 
IPL
 
WPL
 
2013
 
2012
 
2013
 
2012
 
2013
 
2012
Balance, January 1

$101.5

 

$91.1

 

$45.5

 

$56.2

 

$46.9

 

$34.9

Revisions in estimated cash flows (a)
5.6

 
(6.4
)
 
0.1

 
(9.2
)
 
5.5

 
2.8

Liabilities settled
(2.3
)
 
(3.4
)
 
(0.6
)
 
(3.3
)
 
(1.7
)
 
(0.1
)
Liabilities incurred (b)
1.2

 
16.8

 
1.2

 
—

 
—

 
7.7

Accretion expense
3.7

 
3.4

 
1.7

 
1.8

 
1.7

 
1.6

Balance, December 31

$109.7

 

$101.5

 

$47.9

 

$45.5

 

$52.4

 

$46.9


(a)
In 2012, IPL recorded revisions in estimated cash flows of ($8.2) million 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.
WPL [Member]
  
Schedule of Asset Retirement Obligations [Line Items]  
Reconciliation Of Changes In Asset Retirement Obligations (AROs)
A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
 
Alliant Energy
 
IPL
 
WPL
 
2013
 
2012
 
2013
 
2012
 
2013
 
2012
Balance, January 1

$101.5

 

$91.1

 

$45.5

 

$56.2

 

$46.9

 

$34.9

Revisions in estimated cash flows (a)
5.6

 
(6.4
)
 
0.1

 
(9.2
)
 
5.5

 
2.8

Liabilities settled
(2.3
)
 
(3.4
)
 
(0.6
)
 
(3.3
)
 
(1.7
)
 
(0.1
)
Liabilities incurred (b)
1.2

 
16.8

 
1.2

 
—

 
—

 
7.7

Accretion expense
3.7

 
3.4

 
1.7

 
1.8

 
1.7

 
1.6

Balance, December 31

$109.7

 

$101.5

 

$47.9

 

$45.5

 

$52.4

 

$46.9


(a)
In 2012, IPL recorded revisions in estimated cash flows of ($8.2) million 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.