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Asset Retirement Obligations (AROs) (Tables)
 9 Months Ended
Sep. 30, 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)
3.4

 
(9.9
)
 
0.8

 
(9.2
)
 
2.6

 
(0.7
)
Liabilities settled
(0.9
)
 
(2.6
)
 
(0.1
)
 
(2.5
)
 
(0.8
)
 
(0.1
)
Liabilities incurred (b)
—

 
16.0

 
—

 
—

 
—

 
7.6

Accretion expense
2.8

 
2.6

 
1.3

 
1.4

 
1.2

 
1.2

Balance, September 30

$106.8

 

$97.2

 

$47.5

 

$45.9

 

$49.9

 

$42.9


(a)
For the nine months ended September 30, 2012, IPL recorded revisions in estimated cash flows of ($8.2) million based on revised remediation timing and cost information for asbestos remediation at its Sixth Street Generating Station.
(b)
For the nine months ended September 30, 2012, Resources recorded AROs of $8.4 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)
3.4

 
(9.9
)
 
0.8

 
(9.2
)
 
2.6

 
(0.7
)
Liabilities settled
(0.9
)
 
(2.6
)
 
(0.1
)
 
(2.5
)
 
(0.8
)
 
(0.1
)
Liabilities incurred (b)
—

 
16.0

 
—

 
—

 
—

 
7.6

Accretion expense
2.8

 
2.6

 
1.3

 
1.4

 
1.2

 
1.2

Balance, September 30

$106.8

 

$97.2

 

$47.5

 

$45.9

 

$49.9

 

$42.9


(a)
For the nine months ended September 30, 2012, IPL recorded revisions in estimated cash flows of ($8.2) million based on revised remediation timing and cost information for asbestos remediation at its Sixth Street Generating Station.
(b)
For the nine months ended September 30, 2012, Resources recorded AROs of $8.4 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)
3.4

 
(9.9
)
 
0.8

 
(9.2
)
 
2.6

 
(0.7
)
Liabilities settled
(0.9
)
 
(2.6
)
 
(0.1
)
 
(2.5
)
 
(0.8
)
 
(0.1
)
Liabilities incurred (b)
—

 
16.0

 
—

 
—

 
—

 
7.6

Accretion expense
2.8

 
2.6

 
1.3

 
1.4

 
1.2

 
1.2

Balance, September 30

$106.8

 

$97.2

 

$47.5

 

$45.9

 

$49.9

 

$42.9


(a)
For the nine months ended September 30, 2012, IPL recorded revisions in estimated cash flows of ($8.2) million based on revised remediation timing and cost information for asbestos remediation at its Sixth Street Generating Station.
(b)
For the nine months ended September 30, 2012, Resources recorded AROs of $8.4 million related to its Franklin County wind project and WPL recorded AROs of $7.6 million related to Nelson Dewey.