v2.4.0.6
Investments (Summary Financial Information) (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Operating revenues $ 611 $ 575 $ 564
Operating income 326 307 307
Net income 234 218 226
Current assets 67 62  
Non-current assets 3,321 3,100  
Current liabilities 252 299  
Non-current liabilities 1,652 1,490  
WPL [Member]
      
Operating revenues 611 575 564
Operating income 325 308 308
Net income 239 226 221
Current assets 66 61  
Non-current assets 3,292 3,071  
Current liabilities 252 299  
Non-current liabilities $ 1,651 $ 1,487