v2.4.0.6
Document And Entity Information (USD $)
In Billions, except Share data, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
Jan. 31, 2013
Jun. 30, 2012
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2012    
Document Fiscal Year Focus 2012    
Document Fiscal Period Focus FY    
Entity Registrant Name ALLIANT ENERGY CORP    
Entity Central Index Key 0000352541    
Current Fiscal Year End Date --12-31    
Entity Filer Category Large Accelerated Filer    
Entity Common Stock, Shares Outstanding   110,990,924  
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Public Float     $ 5.0
IPL [Member]
      
Entity Registrant Name INTERSTATE POWER & LIGHT CO    
Entity Central Index Key 0000052485    
Entity Filer Category Non-accelerated Filer    
Entity Common Stock, Shares Outstanding   13,370,788  
WPL [Member]
      
Entity Registrant Name WISCONSIN POWER & LIGHT CO    
Entity Central Index Key 0000107832    
Entity Filer Category Non-accelerated Filer    
Entity Common Stock, Shares Outstanding   13,236,601