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Receivables (Details of Accounts Receivable) (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Customer, less allowance for doubtful accounts | $ 84.5 lnt_CustomerAccountsReceivableNet | $ 81.8 lnt_CustomerAccountsReceivableNet
Unbilled utility revenues | 85.4 us-gaap_CostsInExcessOfBillingsOnUncompletedContractsOrProgramsExpectedToBeCollectedWithinOneYear | 92.3 us-gaap_CostsInExcessOfBillingsOnUncompletedContractsOrProgramsExpectedToBeCollectedWithinOneYear
Deferred proceeds | 177.2 lnt_FairValueOfDeferredProceedsOfReceivablesSold | 203.5 lnt_FairValueOfDeferredProceedsOfReceivablesSold
Other, less allowance for doubtful accounts | 80.2 us-gaap_OtherReceivables | 95.7 us-gaap_OtherReceivables
Accounts receivable, less allowance for doubtful accounts | 427.3 us-gaap_AccountsReceivableNetCurrent | 473.3 us-gaap_AccountsReceivableNetCurrent
IPL [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Customer, less allowance for doubtful accounts | 0 lnt_CustomerAccountsReceivableNet / dei_LegalEntityAxis = lnt_IplMember | 0 lnt_CustomerAccountsReceivableNet / dei_LegalEntityAxis = lnt_IplMember
Unbilled utility revenues | 0 us-gaap_CostsInExcessOfBillingsOnUncompletedContractsOrProgramsExpectedToBeCollectedWithinOneYear / dei_LegalEntityAxis = lnt_IplMember | 0 us-gaap_CostsInExcessOfBillingsOnUncompletedContractsOrProgramsExpectedToBeCollectedWithinOneYear / dei_LegalEntityAxis = lnt_IplMember
Deferred proceeds | 177.2 lnt_FairValueOfDeferredProceedsOfReceivablesSold / dei_LegalEntityAxis = lnt_IplMember | 203.5 lnt_FairValueOfDeferredProceedsOfReceivablesSold / dei_LegalEntityAxis = lnt_IplMember
Other, less allowance for doubtful accounts | 39.5 us-gaap_OtherReceivables / dei_LegalEntityAxis = lnt_IplMember | 43.4 us-gaap_OtherReceivables / dei_LegalEntityAxis = lnt_IplMember
Accounts receivable, less allowance for doubtful accounts | 216.7 us-gaap_AccountsReceivableNetCurrent / dei_LegalEntityAxis = lnt_IplMember | 246.9 us-gaap_AccountsReceivableNetCurrent / dei_LegalEntityAxis = lnt_IplMember
WPL [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Customer, less allowance for doubtful accounts | 77.3 lnt_CustomerAccountsReceivableNet / dei_LegalEntityAxis = lnt_WplMember | 73.0 lnt_CustomerAccountsReceivableNet / dei_LegalEntityAxis = lnt_WplMember
Unbilled utility revenues | 85.4 us-gaap_CostsInExcessOfBillingsOnUncompletedContractsOrProgramsExpectedToBeCollectedWithinOneYear / dei_LegalEntityAxis = lnt_WplMember | 92.3 us-gaap_CostsInExcessOfBillingsOnUncompletedContractsOrProgramsExpectedToBeCollectedWithinOneYear / dei_LegalEntityAxis = lnt_WplMember
Other, less allowance for doubtful accounts | 23.1 us-gaap_OtherReceivables / dei_LegalEntityAxis = lnt_WplMember | 33.1 us-gaap_OtherReceivables / dei_LegalEntityAxis = lnt_WplMember
Accounts receivable, less allowance for doubtful accounts | $ 185.8 us-gaap_AccountsReceivableNetCurrent / dei_LegalEntityAxis = lnt_WplMember | $ 198.4 us-gaap_AccountsReceivableNetCurrent / dei_LegalEntityAxis = lnt_WplMember

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- Definition Fair value of deferred proceeds of receivables sold + References No definition available. + Details
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- Definition Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.3-4) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 3 -Subparagraph a(1) -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 4 -Article 5 + Details
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- Definition Amount of receivable reflecting the cost incurred on uncompleted contracts in excess of related billings which is expected to be collected within one year or the normal operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 605 -SubTopic 35 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6802688&loc=d3e57807-111642 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 605 -SubTopic 35 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6802688&loc=d3e57795-111642 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.3(c)(3)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 3 -Subparagraph c(3) -Article 5 + Details
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- Definition Carrying amounts due as of the balance sheet date from parties or arising from transactions not otherwise specified in the taxonomy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.8) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 8 -Article 5 + Details
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