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Investments (Cash Surrender Value Of Life Insurance Policies) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Cash surrender value $ 50.5 $ 49.2
IPL [Member]
   
Cash surrender value 16.0 15.1
WPL [Member]
   
Cash surrender value $ 12.1 $ 11.9