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Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) (IPL [Member], USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
IPL [Member]
    
Receivables [Line Items]    
Collections reinvested in receivables $ 505.9lnt_CollectionsReinvestedInReceivables
/ dei_LegalEntityAxis
= lnt_IplMember		 $ 541.4lnt_CollectionsReinvestedInReceivables
/ dei_LegalEntityAxis
= lnt_IplMember
Credit losses, net of recoveries $ 1.0lnt_CreditLossesNetOfRecoveries
/ dei_LegalEntityAxis
= lnt_IplMember		 $ 2.5lnt_CreditLossesNetOfRecoveries
/ dei_LegalEntityAxis
= lnt_IplMember