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v2.4.1.9

Selected Consolidated Quarterly Financial Data (Unaudited) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified | 3 Months Ended | 12 Months Ended
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Dec. 31, 2014 | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Dec. 31, 2013 | Sep. 30, 2013 | Jun. 30, 2013 | Mar. 31, 2013 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Operating revenues | $ 804.1 us-gaap_Revenues | $ 843.1 us-gaap_Revenues | $ 750.3 us-gaap_Revenues | $ 952.8 us-gaap_Revenues | $ 832.6 us-gaap_Revenues | $ 866.6 us-gaap_Revenues | $ 718.0 us-gaap_Revenues | $ 859.6 us-gaap_Revenues | $ 3,350.3 us-gaap_Revenues | $ 3,276.8 us-gaap_Revenues | $ 3,094.5 us-gaap_Revenues
Operating income | 91.3 us-gaap_OperatingIncomeLoss | 194.8 us-gaap_OperatingIncomeLoss | 103.3 us-gaap_OperatingIncomeLoss | 154.2 us-gaap_OperatingIncomeLoss | 108.6 us-gaap_OperatingIncomeLoss | 201.4 us-gaap_OperatingIncomeLoss | 103.2 us-gaap_OperatingIncomeLoss | 120.7 us-gaap_OperatingIncomeLoss | 543.6 us-gaap_OperatingIncomeLoss | 533.9 us-gaap_OperatingIncomeLoss | 519.7 us-gaap_OperatingIncomeLoss
Income from continuing operations, net of tax | 60.2 us-gaap_IncomeLossFromContinuingOperations | 155.2 us-gaap_IncomeLossFromContinuingOperations | 62.1 us-gaap_IncomeLossFromContinuingOperations | 108.0 us-gaap_IncomeLossFromContinuingOperations | 66.5 us-gaap_IncomeLossFromContinuingOperations | 158.9 us-gaap_IncomeLossFromContinuingOperations | 65.9 us-gaap_IncomeLossFromContinuingOperations | 72.9 us-gaap_IncomeLossFromContinuingOperations | 385.5 us-gaap_IncomeLossFromContinuingOperations | 364.2 us-gaap_IncomeLossFromContinuingOperations | 324.9 us-gaap_IncomeLossFromContinuingOperations
Loss from discontinued operations, net of tax | (0.2)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity | (1.9)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity | (0.3)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity | 0 us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity | (1.0)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity | (1.3)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity | (0.6)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity | (3.0)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity | (2.4)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity | (5.9)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity | (5.1)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity
Net income |  |  |  |  |  |  |  |  | 393.3 us-gaap_NetIncomeLoss | 376.2 us-gaap_NetIncomeLoss | 335.7 us-gaap_NetIncomeLoss
Net income (loss) attributable to common shareowners | 60.0 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 153.3 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 61.8 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 108.0 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 65.5 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 157.6 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 65.3 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 69.9 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 383.1 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 358.3 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 319.8 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic
Income from continuing operations, net of tax (in dollars per share) | $ 0.54 us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare | $ 1.40 us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare | $ 0.56 us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare | $ 0.97 us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare | $ 0.60 us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare | $ 1.43 us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare | $ 0.59 us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare | $ 0.66 us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare |  |  |
Loss from discontinued operations, net of tax (in dollars per share) | $ 0.00 us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare | $ (0.02)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare | $ 0.00 us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare | $ 0.00 us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare | $ (0.01)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare | $ (0.01)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare | $ 0.00 us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare | $ (0.03)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare |  |  |
Net income (in dollars per share) | $ 0.54 us-gaap_EarningsPerShareDiluted | $ 1.38 us-gaap_EarningsPerShareDiluted | $ 0.56 us-gaap_EarningsPerShareDiluted | $ 0.97 us-gaap_EarningsPerShareDiluted | $ 0.59 us-gaap_EarningsPerShareDiluted | $ 1.42 us-gaap_EarningsPerShareDiluted | $ 0.59 us-gaap_EarningsPerShareDiluted | $ 0.63 us-gaap_EarningsPerShareDiluted |  |  |
IPL [Member] |  |  |  |  |  |  |  |  |  |  |
Operating revenues | 431.1 us-gaap_Revenues / dei_LegalEntityAxis = lnt_IplMember | 476.2 us-gaap_Revenues / dei_LegalEntityAxis = lnt_IplMember | 411.9 us-gaap_Revenues / dei_LegalEntityAxis = lnt_IplMember | 528.9 us-gaap_Revenues / dei_LegalEntityAxis = lnt_IplMember | 463.1 us-gaap_Revenues / dei_LegalEntityAxis = lnt_IplMember | 494.4 us-gaap_Revenues / dei_LegalEntityAxis = lnt_IplMember | 383.4 us-gaap_Revenues / dei_LegalEntityAxis = lnt_IplMember | 477.9 us-gaap_Revenues / dei_LegalEntityAxis = lnt_IplMember | 1,848.1 us-gaap_Revenues / dei_LegalEntityAxis = lnt_IplMember | 1,818.8 us-gaap_Revenues / dei_LegalEntityAxis = lnt_IplMember | 1,650.3 us-gaap_Revenues / dei_LegalEntityAxis = lnt_IplMember
Operating income | 23.8 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_IplMember | 93.9 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_IplMember | 34.0 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_IplMember | 57.5 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_IplMember | 36.2 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_IplMember | 100.0 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_IplMember | 34.7 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_IplMember | 41.1 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_IplMember | 209.2 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_IplMember | 212.0 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_IplMember | 200.3 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_IplMember
Net income | 22.6 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_IplMember | 105.1 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_IplMember | 20.9 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_IplMember | 46.0 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_IplMember | 21.1 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_IplMember | 112.6 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_IplMember | 24.7 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_IplMember | 31.5 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_IplMember | 194.6 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_IplMember | 189.9 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_IplMember | 150.2 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_IplMember
Net income (loss) attributable to common shareowners | 20.1 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_IplMember | 102.5 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_IplMember | 18.4 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_IplMember | 43.4 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_IplMember | 18.5 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_IplMember | 110.0 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_IplMember | 22.2 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_IplMember | 22.9 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_IplMember | 184.4 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_IplMember | 173.6 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_IplMember | 137.6 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_IplMember
WPL [Member] |  |  |  |  |  |  |  |  |  |  |
Operating revenues | 359.8 us-gaap_Revenues / dei_LegalEntityAxis = lnt_WplMember | 354.4 us-gaap_Revenues / dei_LegalEntityAxis = lnt_WplMember | 324.5 us-gaap_Revenues / dei_LegalEntityAxis = lnt_WplMember | 410.4 us-gaap_Revenues / dei_LegalEntityAxis = lnt_WplMember | 355.7 us-gaap_Revenues / dei_LegalEntityAxis = lnt_WplMember | 360.9 us-gaap_Revenues / dei_LegalEntityAxis = lnt_WplMember | 319.9 us-gaap_Revenues / dei_LegalEntityAxis = lnt_WplMember | 369.8 us-gaap_Revenues / dei_LegalEntityAxis = lnt_WplMember | 1,449.1 us-gaap_Revenues / dei_LegalEntityAxis = lnt_WplMember | 1,406.3 us-gaap_Revenues / dei_LegalEntityAxis = lnt_WplMember | 1,392.0 us-gaap_Revenues / dei_LegalEntityAxis = lnt_WplMember
Operating income | 59.4 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 93.9 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 60.0 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 87.7 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 67.8 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 95.9 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 59.7 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 72.7 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 301.0 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 296.1 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 284.8 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_WplMember
Net income | 29.8 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 61.6 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 34.6 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 54.8 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 38.2 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 61.3 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 34.4 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 43.6 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 180.8 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 177.5 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 165.7 us-gaap_NetIncomeLoss / dei_LegalEntityAxis = lnt_WplMember
Net income (loss) attributable to common shareowners | $ 29.1 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_WplMember | $ 61.6 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_WplMember | $ 34.6 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_WplMember | $ 54.8 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_WplMember | $ 38.2 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_WplMember | $ 61.3 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_WplMember | $ 34.4 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_WplMember | $ 42.0 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_WplMember | $ 180.1 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_WplMember | $ 175.9 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_WplMember | $ 162.4 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_WplMember

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