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Debt (Schedule Of Debt-To-Capital Ratios) (Details)
Dec. 31, 2014
Actual 52.00%lnt_DebtToCapitalRatiosActualStatus
IPL [Member]  
Actual 47.00%lnt_DebtToCapitalRatiosActualStatus
/ dei_LegalEntityAxis
= lnt_IplMember
WPL [Member]  
Actual 49.00%lnt_DebtToCapitalRatiosActualStatus
/ dei_LegalEntityAxis
= lnt_WplMember
Maximum [Member]  
Requirement, not to exceed 65.00%lnt_DebtToCapitalRatiosBasePercentage
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Maximum [Member] | IPL [Member]  
Requirement, not to exceed 58.00%lnt_DebtToCapitalRatiosBasePercentage
/ dei_LegalEntityAxis
= lnt_IplMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Maximum [Member] | WPL [Member]  
Requirement, not to exceed 58.00%lnt_DebtToCapitalRatiosBasePercentage
/ dei_LegalEntityAxis
= lnt_WplMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember