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Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) (IPL [Member], USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
IPL [Member]
      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Collections reinvested in receivables $ 1,997.9lnt_CollectionsReinvestedInReceivables
/ dei_LegalEntityAxis
= lnt_IplMember		 $ 1,880.8lnt_CollectionsReinvestedInReceivables
/ dei_LegalEntityAxis
= lnt_IplMember		 $ 1,771.6lnt_CollectionsReinvestedInReceivables
/ dei_LegalEntityAxis
= lnt_IplMember
Credit losses, net of recoveries $ 11.4lnt_CreditLossesNetOfRecoveries
/ dei_LegalEntityAxis
= lnt_IplMember		 $ 11.9lnt_CreditLossesNetOfRecoveries
/ dei_LegalEntityAxis
= lnt_IplMember		 $ 10.0lnt_CreditLossesNetOfRecoveries
/ dei_LegalEntityAxis
= lnt_IplMember