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Benefit Plans (Employees Participate In Defined Contribution Retirement Plans) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
401(k) costs $ 5.4 $ 5.2
IPL [Member]
   
401(k) costs 2.8 [1] 2.7 [1]
WPL [Member]
   
401(k) costs $ 2.3 [1] $ 2.3 [1]
[1] IPL’s and WPL’s amounts include allocated costs associated with Corporate Services employees.