XML 149 R110.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Benefit Plans (Amounts Recognized On The Consolidated Balance Sheets) (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Amounts recognized on the balance sheets consist of: |  |  |  |
Pension and other benefit obligations | $ (421.7)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent |  | $ (206.6)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent |
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a): |  |  |  |
Regulatory liability recognized related to other postretirement benefit plans | 1.1 lnt_DefinedBenefitPlanRegulatoryLiabilityBeforeTax |  | 5.1 lnt_DefinedBenefitPlanRegulatoryLiabilityBeforeTax |
Pension Plans, Defined Benefit [Member] |  |  |  |
Amounts recognized on the balance sheets consist of: |  |  |  |
Non-current assets | 0 lnt_PensionAndOtherPostretirementDefinedBenefitPlansNonCurrentAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  | 0 lnt_PensionAndOtherPostretirementDefinedBenefitPlansNonCurrentAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |
Other current liabilities | (2.5)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  | (2.4)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |
Pension and other benefit obligations | (280.9)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  | (88.1)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |
Net amounts recognized at December 31 | (283.4)us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  | (90.5)us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a): |  |  |  |
Net actuarial loss | 533.4 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetGainLossBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | [1] | 348.6 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetGainLossBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | [1]
Prior service credit | (7.4)lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | [1] | (7.4)lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | [1]
Net amount recognized at December 31 | 526.0 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetsRegulatoryLiabilitiesAndOtherComprehensiveIncome / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | [1] | 341.2 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetsRegulatoryLiabilitiesAndOtherComprehensiveIncome / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | [1]
Other Postretirement Benefits Plans [Member] |  |  |  |
Amounts recognized on the balance sheets consist of: |  |  |  |
Non-current assets | 6.1 lnt_PensionAndOtherPostretirementDefinedBenefitPlansNonCurrentAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  | 14.5 lnt_PensionAndOtherPostretirementDefinedBenefitPlansNonCurrentAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |
Other current liabilities | (5.6)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  | (4.8)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |
Pension and other benefit obligations | (110.0)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  | (93.5)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |
Net amounts recognized at December 31 | (109.5)us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  | (83.8)us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a): |  |  |  |
Net actuarial loss | 60.7 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetGainLossBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | [1] | 38.1 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetGainLossBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | [1]
Prior service credit | (16.7)lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | [1] | (28.6)lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | [1]
Net amount recognized at December 31 | 44.0 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetsRegulatoryLiabilitiesAndOtherComprehensiveIncome / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | [1] | 9.5 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetsRegulatoryLiabilitiesAndOtherComprehensiveIncome / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | [1]
IPL [Member] |  |  |  |
Amounts recognized on the balance sheets consist of: |  |  |  |
Pension and other benefit obligations | (142.4)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / dei_LegalEntityAxis = lnt_IplMember |  | (48.6)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / dei_LegalEntityAxis = lnt_IplMember |
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a): |  |  |  |
Regulatory liability recognized related to other postretirement benefit plans | 0 lnt_DefinedBenefitPlanRegulatoryLiabilityBeforeTax / dei_LegalEntityAxis = lnt_IplMember |  | 1.0 lnt_DefinedBenefitPlanRegulatoryLiabilityBeforeTax / dei_LegalEntityAxis = lnt_IplMember |
IPL [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |
Amounts recognized on the balance sheets consist of: |  |  |  |
Non-current assets | 0 lnt_PensionAndOtherPostretirementDefinedBenefitPlansNonCurrentAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember |  | 0 lnt_PensionAndOtherPostretirementDefinedBenefitPlansNonCurrentAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember |
Other current liabilities | (0.8)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember |  | (0.8)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember |
Pension and other benefit obligations | (117.6)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember |  | (27.3)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember |
Net amounts recognized at December 31 | (118.4)us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember |  | (28.1)us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember |
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a): |  |  |  |
Net actuarial loss | 233.1 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetGainLossBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember | [2] | 146.1 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetGainLossBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember | [2]
Prior service credit | (2.6)lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember | [2] | (2.6)lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember | [2]
Net amount recognized at December 31 | 230.5 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetsRegulatoryLiabilitiesAndOtherComprehensiveIncome / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember | [2] | 143.5 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetsRegulatoryLiabilitiesAndOtherComprehensiveIncome / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember | [2]
IPL [Member] | Other Postretirement Benefits Plans [Member] |  |  |  |
Amounts recognized on the balance sheets consist of: |  |  |  |
Non-current assets | 1.2 lnt_PensionAndOtherPostretirementDefinedBenefitPlansNonCurrentAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember |  | 8.8 lnt_PensionAndOtherPostretirementDefinedBenefitPlansNonCurrentAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember |
Other current liabilities | 0 us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember |  | 0 us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember |
Pension and other benefit obligations | (18.9)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember |  | (15.4)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember |
Net amounts recognized at December 31 | (17.7)us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember |  | (6.6)us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember |
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a): |  |  |  |
Net actuarial loss | 27.9 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetGainLossBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember | [2] | 18.2 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetGainLossBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember | [2]
Prior service credit | (8.7)lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember | [2] | (15.0)lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember | [2]
Net amount recognized at December 31 | 19.2 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetsRegulatoryLiabilitiesAndOtherComprehensiveIncome / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember | [2] | 3.2 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetsRegulatoryLiabilitiesAndOtherComprehensiveIncome / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_IplMember | [2]
WPL [Member] |  |  |  |
Amounts recognized on the balance sheets consist of: |  |  |  |
Pension and other benefit obligations | (180.4)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / dei_LegalEntityAxis = lnt_WplMember |  | (88.4)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / dei_LegalEntityAxis = lnt_WplMember |
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a): |  |  |  |
Regulatory liability recognized related to other postretirement benefit plans | 1.1 lnt_DefinedBenefitPlanRegulatoryLiabilityBeforeTax / dei_LegalEntityAxis = lnt_WplMember |  | 1.1 lnt_DefinedBenefitPlanRegulatoryLiabilityBeforeTax / dei_LegalEntityAxis = lnt_WplMember |
WPL [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |
Amounts recognized on the balance sheets consist of: |  |  |  |
Non-current assets | 0 lnt_PensionAndOtherPostretirementDefinedBenefitPlansNonCurrentAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember |  | 0 lnt_PensionAndOtherPostretirementDefinedBenefitPlansNonCurrentAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember |
Other current liabilities | (0.1)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember |  | (0.2)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember |
Pension and other benefit obligations | (107.2)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember |  | (21.8)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember |
Net amounts recognized at December 31 | (107.3)us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember |  | (22.0)us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember |
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a): |  |  |  |
Net actuarial loss | 233.5 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetGainLossBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember | [3] | 152.2 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetGainLossBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember | [3]
Prior service credit | (1.0)lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember | [3] | (0.7)lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember | [3]
Net amount recognized at December 31 | 232.5 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetsRegulatoryLiabilitiesAndOtherComprehensiveIncome / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember | [3] | 151.5 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetsRegulatoryLiabilitiesAndOtherComprehensiveIncome / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember | [3]
WPL [Member] | Other Postretirement Benefits Plans [Member] |  |  |  |
Amounts recognized on the balance sheets consist of: |  |  |  |
Non-current assets | 4.9 lnt_PensionAndOtherPostretirementDefinedBenefitPlansNonCurrentAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember |  | 5.8 lnt_PensionAndOtherPostretirementDefinedBenefitPlansNonCurrentAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember |
Other current liabilities | (5.5)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember |  | (4.8)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember |
Pension and other benefit obligations | (71.6)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember |  | (64.9)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember |
Net amounts recognized at December 31 | (72.2)us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember |  | (63.9)us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember |
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a): |  |  |  |
Net actuarial loss | 26.3 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetGainLossBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember | [3] | 18.3 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetGainLossBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember | [3]
Prior service credit | (5.6)lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember | [3] | (9.5)lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetAndRegulatoryLiabilityAndOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember | [3]
Net amount recognized at December 31 | $ 20.7 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetsRegulatoryLiabilitiesAndOtherComprehensiveIncome / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember | [3] | $ 8.8 lnt_DefinedBenefitPlanAmountsRecognizedInRegulatoryAssetsRegulatoryLiabilitiesAndOtherComprehensiveIncome / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = lnt_WplMember | [3]
[1] | Refer to Note 2 and Alliant Energy’s common equity statements for amounts recognized in “Regulatory assets” and “AOCL,” respectively, on Alliant Energy’s balance sheets. At December 31, 2014 and 2013, $1.1 million and $5.1 million, respectively, of regulatory liabilities were recognized related to Alliant Energy’s OPEB plans.
[2] | Refer to Note 2 for amounts recognized in “Regulatory assets” on IPL’s balance sheets. At December 31, 2014 and 2013, $0 and $1.0 million, respectively, of regulatory liabilities were recognized related to IPL’s OPEB plans.
[3] | Refer to Note 2 for amounts recognized in “Regulatory assets” on WPL’s balance sheets. At December 31, 2014 and 2013, $1.1 million and $1.1 million, respectively, of regulatory liabilities were recognized related to WPL’s OPEB plans.

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