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Asset Retirement Obligations (AROs) (Tables)
 3 Months Ended
Mar. 31, 2012
Asset Retirement Obligations (AROs) [Abstract]  
Reconciliation Of Changes In Asset Retirement Obligations (AROs)
     Alliant Energy     IPL     WPL  
     2012     2011     2012     2011     2012     2011  

Balance, Jan. 1

    $ 91.1      $ 75.9      $ 56.2      $ 43.6      $ 34.9      $ 32.3   

Revisions in estimated cash flows (a)

      (8.2 )      (0.3 )      (8.2 )      —          —          (0.3 ) 

Liabilities settled

      (1.0 )      (0.1 )      (0.9 )      (0.1 )      (0.1 )      —     

Accretion expense

      0.9        1.1        0.5        0.7        0.4        0.4   
  

 

 

    

 

 

    

 

 

    

 

 

    

 

 

    

 

 

  

Balance, March 31

    $ 82.8      $ 76.6      $ 47.6      $ 44.2      $ 35.2      $ 32.4   
  

 

 

    

 

 

    

 

 

    

 

 

    

 

 

    

 

 

  

 

(a)
In the first quarter of 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.