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v2.4.1.9

Summary Of Significant Accounting Policies (Narrative) (Details) (Minimum [Member]) | Mar. 31, 2015
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New Accounting Pronouncements or Change in Accounting Principle [Line Items] |
Debt issuance costs percentage, on total long-term debt | 1.00%lnt_DebtIssuanceCostsPercentageOnLongtermDebt
IPL [Member] |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |
Debt issuance costs percentage, on total long-term debt | 1.00%lnt_DebtIssuanceCostsPercentageOnLongtermDebt / dei_LegalEntityAxis = lnt_IplMember / us-gaap_RangeAxis = us-gaap_MinimumMember
WPL [Member] |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |
Debt issuance costs percentage, on total long-term debt | 1.00%lnt_DebtIssuanceCostsPercentageOnLongtermDebt / dei_LegalEntityAxis = lnt_WplMember / us-gaap_RangeAxis = us-gaap_MinimumMember

X
- Definition Debt Issuance Costs Percentage On Long-term Debt + References No definition available. + Details
Name: | lnt_DebtIssuanceCostsPercentageOnLongtermDebt
Namespace Prefix: | lnt_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration