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v2.4.1.9

Income Taxes (Schedule Of Effective Income Tax Rates) (Details) | 3 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014
Effective Tax Rate [Line Items] |  |
Statutory federal income tax rate | 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate | 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
IPL's tax benefit riders | (9.90%)lnt_EffectiveIncomeTaxRateReconciliationTaxBenefitRider | (11.90%)lnt_EffectiveIncomeTaxRateReconciliationTaxBenefitRider
Production tax credits | (6.20%)us-gaap_EffectiveIncomeTaxRateReconciliationDeductionsQualifiedProductionActivities | (6.70%)us-gaap_EffectiveIncomeTaxRateReconciliationDeductionsQualifiedProductionActivities
Effect of rate-making on property-related differences | (6.10%)lnt_EffectiveIncomeTaxRateReconciliationEffectOfRateMakingOnPropertyRelatedDifferences | (5.30%)lnt_EffectiveIncomeTaxRateReconciliationEffectOfRateMakingOnPropertyRelatedDifferences
Other items, net | 4.30%us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments | 4.60%us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments
Overall income tax rate | 17.10%us-gaap_EffectiveIncomeTaxRateContinuingOperations | 15.70%us-gaap_EffectiveIncomeTaxRateContinuingOperations
IPL [Member] |  |
Effective Tax Rate [Line Items] |  |
Statutory federal income tax rate | 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate / dei_LegalEntityAxis = lnt_IplMember | 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate / dei_LegalEntityAxis = lnt_IplMember
IPL's tax benefit riders | (25.20%)lnt_EffectiveIncomeTaxRateReconciliationTaxBenefitRider / dei_LegalEntityAxis = lnt_IplMember | (31.20%)lnt_EffectiveIncomeTaxRateReconciliationTaxBenefitRider / dei_LegalEntityAxis = lnt_IplMember
Production tax credits | (7.30%)us-gaap_EffectiveIncomeTaxRateReconciliationDeductionsQualifiedProductionActivities / dei_LegalEntityAxis = lnt_IplMember | (8.30%)us-gaap_EffectiveIncomeTaxRateReconciliationDeductionsQualifiedProductionActivities / dei_LegalEntityAxis = lnt_IplMember
Effect of rate-making on property-related differences | (14.60%)lnt_EffectiveIncomeTaxRateReconciliationEffectOfRateMakingOnPropertyRelatedDifferences / dei_LegalEntityAxis = lnt_IplMember | (12.40%)lnt_EffectiveIncomeTaxRateReconciliationEffectOfRateMakingOnPropertyRelatedDifferences / dei_LegalEntityAxis = lnt_IplMember
Other items, net | 4.40%us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments / dei_LegalEntityAxis = lnt_IplMember | 4.70%us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments / dei_LegalEntityAxis = lnt_IplMember
Overall income tax rate | (7.70%)us-gaap_EffectiveIncomeTaxRateContinuingOperations / dei_LegalEntityAxis = lnt_IplMember | (12.20%)us-gaap_EffectiveIncomeTaxRateContinuingOperations / dei_LegalEntityAxis = lnt_IplMember
WPL [Member] |  |
Effective Tax Rate [Line Items] |  |
Statutory federal income tax rate | 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate / dei_LegalEntityAxis = lnt_WplMember | 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate / dei_LegalEntityAxis = lnt_WplMember
Production tax credits | (6.00%)us-gaap_EffectiveIncomeTaxRateReconciliationDeductionsQualifiedProductionActivities / dei_LegalEntityAxis = lnt_WplMember | (6.40%)us-gaap_EffectiveIncomeTaxRateReconciliationDeductionsQualifiedProductionActivities / dei_LegalEntityAxis = lnt_WplMember
Effect of rate-making on property-related differences | (0.60%)lnt_EffectiveIncomeTaxRateReconciliationEffectOfRateMakingOnPropertyRelatedDifferences / dei_LegalEntityAxis = lnt_WplMember | (1.00%)lnt_EffectiveIncomeTaxRateReconciliationEffectOfRateMakingOnPropertyRelatedDifferences / dei_LegalEntityAxis = lnt_WplMember
Other items, net | 4.60%us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments / dei_LegalEntityAxis = lnt_WplMember | 4.80%us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments / dei_LegalEntityAxis = lnt_WplMember
Overall income tax rate | 33.00%us-gaap_EffectiveIncomeTaxRateContinuingOperations / dei_LegalEntityAxis = lnt_WplMember | 32.40%us-gaap_EffectiveIncomeTaxRateContinuingOperations / dei_LegalEntityAxis = lnt_WplMember

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- Definition Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(h)(2)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph h -Subparagraph 2 -Article 4 + Details
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- Definition Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to deduction for qualified production activity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 6.I) -URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319 + Details
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