XML 173 R5.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Consolidated Statements Of Cash Flows (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Cash flows from operating activities: |  |  |
Net income | $ 393.3 us-gaap_NetIncomeLoss | $ 376.2 us-gaap_NetIncomeLoss | $ 335.7 us-gaap_NetIncomeLoss
Adjustments to reconcile net income to net cash flows from operating activities: |  |  |
Depreciation and amortization | 388.1 lnt_AdjustmentDepreciationAndAmortizationIncludingDiscontinuedOperations | 370.9 lnt_AdjustmentDepreciationAndAmortizationIncludingDiscontinuedOperations | 332.9 lnt_AdjustmentDepreciationAndAmortizationIncludingDiscontinuedOperations
Other amortizations | 54.2 us-gaap_OtherAmortizationOfDeferredCharges | 40.2 us-gaap_OtherAmortizationOfDeferredCharges | 55.0 us-gaap_OtherAmortizationOfDeferredCharges
Deferred tax expense (benefit) and investment tax credits | 55.2 us-gaap_DeferredIncomeTaxesAndTaxCredits | 108.3 us-gaap_DeferredIncomeTaxesAndTaxCredits | 143.3 us-gaap_DeferredIncomeTaxesAndTaxCredits
Equity (income) loss from unconsolidated investments, net | (40.4)us-gaap_IncomeLossFromEquityMethodInvestments | (43.7)us-gaap_IncomeLossFromEquityMethodInvestments | (41.3)us-gaap_IncomeLossFromEquityMethodInvestments
Distributions from equity method investments | 36.4 us-gaap_EquityMethodInvestmentDividendsOrDistributions | 35.4 us-gaap_EquityMethodInvestmentDividendsOrDistributions | 34.2 us-gaap_EquityMethodInvestmentDividendsOrDistributions
Equity component of allowance for funds used during construction | (23.1)us-gaap_IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction | (20.3)us-gaap_IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction | (14.1)us-gaap_IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction
Other | 2.0 us-gaap_OtherNoncashIncomeExpense | (3.7)us-gaap_OtherNoncashIncomeExpense | 0.7 us-gaap_OtherNoncashIncomeExpense
Other changes in assets and liabilities: |  |  |
Accounts receivable | 48.7 us-gaap_IncreaseDecreaseInAccountsReceivable | (49.2)us-gaap_IncreaseDecreaseInAccountsReceivable | 61.3 us-gaap_IncreaseDecreaseInAccountsReceivable
Sales of accounts receivable | (7.0)us-gaap_IncreaseDecreaseInOtherReceivables | (101.0)us-gaap_IncreaseDecreaseInOtherReceivables | (10.0)us-gaap_IncreaseDecreaseInOtherReceivables
Regulatory assets | (439.8)us-gaap_IncreaseDecreaseInOtherRegulatoryAssets | 140.5 us-gaap_IncreaseDecreaseInOtherRegulatoryAssets | (178.1)us-gaap_IncreaseDecreaseInOtherRegulatoryAssets
Regulatory liabilities | 10.8 us-gaap_IncreaseDecreaseInRegulatoryLiabilities | (90.8)us-gaap_IncreaseDecreaseInRegulatoryLiabilities | 16.4 us-gaap_IncreaseDecreaseInRegulatoryLiabilities
Deferred income taxes | 138.4 us-gaap_IncreaseDecreaseInDeferredIncomeTaxes | 101.9 us-gaap_IncreaseDecreaseInDeferredIncomeTaxes | 69.7 us-gaap_IncreaseDecreaseInDeferredIncomeTaxes
Pension and other benefit obligations | 215.1 us-gaap_IncreaseDecreaseInPensionAndPostretirementObligations | (157.4)us-gaap_IncreaseDecreaseInPensionAndPostretirementObligations | 51.3 us-gaap_IncreaseDecreaseInPensionAndPostretirementObligations
Other | 59.7 us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet | 23.7 us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet | (15.9)us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet
Net cash flows from operating activities | 891.6 us-gaap_NetCashProvidedByUsedInOperatingActivities | 731.0 us-gaap_NetCashProvidedByUsedInOperatingActivities | 841.1 us-gaap_NetCashProvidedByUsedInOperatingActivities
Cash flows used for investing activities: |  |  |
Utility business - purchase of Riverside Energy Center | 0 lnt_PaymentsToAcquireProductiveAssetsBusinessLine1 | 0 lnt_PaymentsToAcquireProductiveAssetsBusinessLine1 | (403.5)lnt_PaymentsToAcquireProductiveAssetsBusinessLine1
Utility business - other | (838.9)lnt_PaymentsToAcquireProductiveAssetsOther | (731.6)lnt_PaymentsToAcquireProductiveAssetsOther | (622.0)lnt_PaymentsToAcquireProductiveAssetsOther
Alliant Energy Corporate Services, Inc. and non-regulated businesses | (63.9)lnt_PaymentsToAcquireProductiveAssetsBusinessLine2 | (66.7)lnt_PaymentsToAcquireProductiveAssetsBusinessLine2 | (132.6)lnt_PaymentsToAcquireProductiveAssetsBusinessLine2
Proceeds from Franklin County wind project cash grant | 0 lnt_ProceedsFromCashGrant | 62.4 lnt_ProceedsFromCashGrant | 0 lnt_ProceedsFromCashGrant
Other | (14.9)us-gaap_PaymentsForProceedsFromOtherInvestingActivities | (18.8)us-gaap_PaymentsForProceedsFromOtherInvestingActivities | 2.6 us-gaap_PaymentsForProceedsFromOtherInvestingActivities
Net cash flows used for investing activities | (917.7)us-gaap_NetCashProvidedByUsedInInvestingActivities | (754.7)us-gaap_NetCashProvidedByUsedInInvestingActivities | (1,155.5)us-gaap_NetCashProvidedByUsedInInvestingActivities
Cash flows from (used for) financing activities: |  |  |
Common stock dividends | (225.8)us-gaap_PaymentsOfDividendsCommonStock | (208.3)us-gaap_PaymentsOfDividendsCommonStock | (199.3)us-gaap_PaymentsOfDividendsCommonStock
Preferred dividends paid by subsidiaries | (10.2)us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock | (11.4)us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock | (15.9)us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock
Payments to redeem cumulative preferred stock | 0 us-gaap_PaymentsForRepurchaseOfRedeemablePreferredStock | (211.0)us-gaap_PaymentsForRepurchaseOfRedeemablePreferredStock | 0 us-gaap_PaymentsForRepurchaseOfRedeemablePreferredStock
Proceeds from issuance of cumulative preferred stock of IPL | 0 us-gaap_ProceedsFromIssuanceOfRedeemablePreferredStock | 200.0 us-gaap_ProceedsFromIssuanceOfRedeemablePreferredStock | 0 us-gaap_ProceedsFromIssuanceOfRedeemablePreferredStock
Proceeds from issuance of long-term debt | 812.9 us-gaap_ProceedsFromIssuanceOfLongTermDebt | 250.0 us-gaap_ProceedsFromIssuanceOfLongTermDebt | 385.0 us-gaap_ProceedsFromIssuanceOfLongTermDebt
Payments to retire long-term debt | (358.5)us-gaap_RepaymentsOfLongTermDebt | (1.5)us-gaap_RepaymentsOfLongTermDebt | (1.4)us-gaap_RepaymentsOfLongTermDebt
Net change in commercial paper | (138.1)us-gaap_ProceedsFromRepaymentsOfShortTermDebt | 11.9 us-gaap_ProceedsFromRepaymentsOfShortTermDebt | 164.7 us-gaap_ProceedsFromRepaymentsOfShortTermDebt
Other | (7.1)us-gaap_ProceedsFromPaymentsForOtherFinancingActivities | (17.4)us-gaap_ProceedsFromPaymentsForOtherFinancingActivities | (8.9)us-gaap_ProceedsFromPaymentsForOtherFinancingActivities
Net cash flows from (used for) financing activities | 73.2 us-gaap_NetCashProvidedByUsedInFinancingActivities | 12.3 us-gaap_NetCashProvidedByUsedInFinancingActivities | 324.2 us-gaap_NetCashProvidedByUsedInFinancingActivities
Net increase (decrease) in cash and cash equivalents | 47.1 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease | (11.4)us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease | 9.8 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease
Cash and cash equivalents at beginning of period | 9.8 us-gaap_CashAndCashEquivalentsAtCarryingValue | 21.2 us-gaap_CashAndCashEquivalentsAtCarryingValue | 11.4 us-gaap_CashAndCashEquivalentsAtCarryingValue
Cash and cash equivalents at end of period | 56.9 us-gaap_CashAndCashEquivalentsAtCarryingValue | 9.8 us-gaap_CashAndCashEquivalentsAtCarryingValue | 21.2 us-gaap_CashAndCashEquivalentsAtCarryingValue
Supplemental cash flows information: |  |  |
Interest, net of capitalized interest | (180.8)us-gaap_InterestPaidNet | (171.7)us-gaap_InterestPaidNet | (155.2)us-gaap_InterestPaidNet
Income taxes, net | 5.3 us-gaap_IncomeTaxesPaidNet | 9.6 us-gaap_IncomeTaxesPaidNet | 20.3 us-gaap_IncomeTaxesPaidNet
Significant non-cash investing and financing activities: |  |  |
Accrued capital expenditures | 160.3 us-gaap_CapitalExpendituresIncurredButNotYetPaid | 103.8 us-gaap_CapitalExpendituresIncurredButNotYetPaid | 105.3 us-gaap_CapitalExpendituresIncurredButNotYetPaid
IPL [Member] |  |  |
Cash flows from operating activities: |  |  |
Net income | 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
Adjustments to reconcile net income to net cash flows from operating activities: |  |  |
Depreciation and amortization | 197.5 lnt_DepreciationAndAmortizationCashFlow / dei_LegalEntityAxis = lnt_IplMember | 191.1 lnt_DepreciationAndAmortizationCashFlow / dei_LegalEntityAxis = lnt_IplMember | 188.9 lnt_DepreciationAndAmortizationCashFlow / dei_LegalEntityAxis = lnt_IplMember
Deferred tax expense (benefit) and investment tax credits | (9.7)us-gaap_DeferredIncomeTaxesAndTaxCredits / dei_LegalEntityAxis = lnt_IplMember | 4.2 us-gaap_DeferredIncomeTaxesAndTaxCredits / dei_LegalEntityAxis = lnt_IplMember | 19.3 us-gaap_DeferredIncomeTaxesAndTaxCredits / dei_LegalEntityAxis = lnt_IplMember
Equity component of allowance for funds used during construction | (17.1)us-gaap_IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction / dei_LegalEntityAxis = lnt_IplMember | (13.8)us-gaap_IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction / dei_LegalEntityAxis = lnt_IplMember | (5.2)us-gaap_IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction / dei_LegalEntityAxis = lnt_IplMember
Other | 11.3 us-gaap_OtherNoncashIncomeExpense / dei_LegalEntityAxis = lnt_IplMember | (0.7)us-gaap_OtherNoncashIncomeExpense / dei_LegalEntityAxis = lnt_IplMember | 10.6 us-gaap_OtherNoncashIncomeExpense / dei_LegalEntityAxis = lnt_IplMember
Other changes in assets and liabilities: |  |  |
Accounts receivable | 43.3 us-gaap_IncreaseDecreaseInAccountsReceivable / dei_LegalEntityAxis = lnt_IplMember | (55.9)us-gaap_IncreaseDecreaseInAccountsReceivable / dei_LegalEntityAxis = lnt_IplMember | (0.7)us-gaap_IncreaseDecreaseInAccountsReceivable / dei_LegalEntityAxis = lnt_IplMember
Sales of accounts receivable | (7.0)us-gaap_IncreaseDecreaseInOtherReceivables / dei_LegalEntityAxis = lnt_IplMember | (101.0)us-gaap_IncreaseDecreaseInOtherReceivables / dei_LegalEntityAxis = lnt_IplMember | (10.0)us-gaap_IncreaseDecreaseInOtherReceivables / dei_LegalEntityAxis = lnt_IplMember
Regulatory assets | (272.9)us-gaap_IncreaseDecreaseInOtherRegulatoryAssets / dei_LegalEntityAxis = lnt_IplMember | 71.4 us-gaap_IncreaseDecreaseInOtherRegulatoryAssets / dei_LegalEntityAxis = lnt_IplMember | (129.0)us-gaap_IncreaseDecreaseInOtherRegulatoryAssets / dei_LegalEntityAxis = lnt_IplMember
Regulatory liabilities | (18.9)us-gaap_IncreaseDecreaseInRegulatoryLiabilities / dei_LegalEntityAxis = lnt_IplMember | (82.3)us-gaap_IncreaseDecreaseInRegulatoryLiabilities / dei_LegalEntityAxis = lnt_IplMember | (12.1)us-gaap_IncreaseDecreaseInRegulatoryLiabilities / dei_LegalEntityAxis = lnt_IplMember
Deferred income taxes | 140.4 us-gaap_IncreaseDecreaseInDeferredIncomeTaxes / dei_LegalEntityAxis = lnt_IplMember | 92.4 us-gaap_IncreaseDecreaseInDeferredIncomeTaxes / dei_LegalEntityAxis = lnt_IplMember | 64.6 us-gaap_IncreaseDecreaseInDeferredIncomeTaxes / dei_LegalEntityAxis = lnt_IplMember
Pension and other benefit obligations | 93.8 us-gaap_IncreaseDecreaseInPensionAndPostretirementObligations / dei_LegalEntityAxis = lnt_IplMember | (74.3)us-gaap_IncreaseDecreaseInPensionAndPostretirementObligations / dei_LegalEntityAxis = lnt_IplMember | 21.0 us-gaap_IncreaseDecreaseInPensionAndPostretirementObligations / dei_LegalEntityAxis = lnt_IplMember
Other | 50.8 us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet / dei_LegalEntityAxis = lnt_IplMember | 11.6 us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet / dei_LegalEntityAxis = lnt_IplMember | (6.6)us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet / dei_LegalEntityAxis = lnt_IplMember
Net cash flows from operating activities | 406.1 us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = lnt_IplMember | 232.6 us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = lnt_IplMember | 291.0 us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = lnt_IplMember
Cash flows used for investing activities: |  |  |
Utility business - other | (526.0)lnt_PaymentsToAcquireProductiveAssetsOther / dei_LegalEntityAxis = lnt_IplMember | (400.2)lnt_PaymentsToAcquireProductiveAssetsOther / dei_LegalEntityAxis = lnt_IplMember | (307.5)lnt_PaymentsToAcquireProductiveAssetsOther / dei_LegalEntityAxis = lnt_IplMember
Other | (26.7)us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = lnt_IplMember | (23.1)us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = lnt_IplMember | (23.7)us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = lnt_IplMember
Net cash flows used for investing activities | (552.7)us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = lnt_IplMember | (423.3)us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = lnt_IplMember | (331.2)us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = lnt_IplMember
Cash flows from (used for) financing activities: |  |  |
Common stock dividends | (140.0)us-gaap_PaymentsOfDividendsCommonStock / dei_LegalEntityAxis = lnt_IplMember | (128.1)us-gaap_PaymentsOfDividendsCommonStock / dei_LegalEntityAxis = lnt_IplMember | (122.9)us-gaap_PaymentsOfDividendsCommonStock / dei_LegalEntityAxis = lnt_IplMember
Preferred dividends paid by subsidiaries | (10.2)us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock / dei_LegalEntityAxis = lnt_IplMember | (10.8)us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock / dei_LegalEntityAxis = lnt_IplMember | (12.6)us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock / dei_LegalEntityAxis = lnt_IplMember
Capital contributions from parent | 90.0 us-gaap_ProceedsFromContributionsFromParent / dei_LegalEntityAxis = lnt_IplMember | 120.0 us-gaap_ProceedsFromContributionsFromParent / dei_LegalEntityAxis = lnt_IplMember | 110.0 us-gaap_ProceedsFromContributionsFromParent / dei_LegalEntityAxis = lnt_IplMember
Payments to redeem cumulative preferred stock | 0 us-gaap_PaymentsForRepurchaseOfRedeemablePreferredStock / dei_LegalEntityAxis = lnt_IplMember | (150.0)us-gaap_PaymentsForRepurchaseOfRedeemablePreferredStock / dei_LegalEntityAxis = lnt_IplMember | 0 us-gaap_PaymentsForRepurchaseOfRedeemablePreferredStock / dei_LegalEntityAxis = lnt_IplMember
Proceeds from issuance of cumulative preferred stock of IPL | 0 us-gaap_ProceedsFromIssuanceOfRedeemablePreferredStock / dei_LegalEntityAxis = lnt_IplMember | 200.0 us-gaap_ProceedsFromIssuanceOfRedeemablePreferredStock / dei_LegalEntityAxis = lnt_IplMember | 0 us-gaap_ProceedsFromIssuanceOfRedeemablePreferredStock / dei_LegalEntityAxis = lnt_IplMember
Proceeds from issuance of long-term debt | 250.0 us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = lnt_IplMember | 250.0 us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = lnt_IplMember | 0 us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = lnt_IplMember
Payments to retire long-term debt | (38.4)us-gaap_RepaymentsOfLongTermDebt / dei_LegalEntityAxis = lnt_IplMember | 0 us-gaap_RepaymentsOfLongTermDebt / dei_LegalEntityAxis = lnt_IplMember | 0 us-gaap_RepaymentsOfLongTermDebt / dei_LegalEntityAxis = lnt_IplMember
Net change in commercial paper | 0 us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = lnt_IplMember | (76.3)us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = lnt_IplMember | 69.2 us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = lnt_IplMember
Other | (3.9)us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = lnt_IplMember | (14.2)us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = lnt_IplMember | (1.1)us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = lnt_IplMember
Net cash flows from (used for) financing activities | 147.5 us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = lnt_IplMember | 190.6 us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = lnt_IplMember | 42.6 us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = lnt_IplMember
Net increase (decrease) in cash and cash equivalents | 0.9 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = lnt_IplMember | (0.1)us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = lnt_IplMember | 2.4 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = lnt_IplMember
Cash and cash equivalents at beginning of period | 4.4 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = lnt_IplMember | 4.5 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = lnt_IplMember | 2.1 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = lnt_IplMember
Cash and cash equivalents at end of period | 5.3 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = lnt_IplMember | 4.4 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = lnt_IplMember | 4.5 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = lnt_IplMember
Supplemental cash flows information: |  |  |
Interest, net of capitalized interest | (89.8)us-gaap_InterestPaidNet / dei_LegalEntityAxis = lnt_IplMember | (80.7)us-gaap_InterestPaidNet / dei_LegalEntityAxis = lnt_IplMember | (78.3)us-gaap_InterestPaidNet / dei_LegalEntityAxis = lnt_IplMember
Income taxes, net | 20.1 us-gaap_IncomeTaxesPaidNet / dei_LegalEntityAxis = lnt_IplMember | 0.1 us-gaap_IncomeTaxesPaidNet / dei_LegalEntityAxis = lnt_IplMember | (3.3)us-gaap_IncomeTaxesPaidNet / dei_LegalEntityAxis = lnt_IplMember
Significant non-cash investing and financing activities: |  |  |
Accrued capital expenditures | 113.2 us-gaap_CapitalExpendituresIncurredButNotYetPaid / dei_LegalEntityAxis = lnt_IplMember | 58.1 us-gaap_CapitalExpendituresIncurredButNotYetPaid / dei_LegalEntityAxis = lnt_IplMember | 53.4 us-gaap_CapitalExpendituresIncurredButNotYetPaid / dei_LegalEntityAxis = lnt_IplMember
WPL [Member] |  |  |
Cash flows from operating activities: |  |  |
Net income | 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
Adjustments to reconcile net income to net cash flows from operating activities: |  |  |
Depreciation and amortization | 181.2 lnt_DepreciationAndAmortizationCashFlow / dei_LegalEntityAxis = lnt_WplMember | 172.2 lnt_DepreciationAndAmortizationCashFlow / dei_LegalEntityAxis = lnt_WplMember | 140.9 lnt_DepreciationAndAmortizationCashFlow / dei_LegalEntityAxis = lnt_WplMember
Other amortizations | 47.3 us-gaap_OtherAmortizationOfDeferredCharges / dei_LegalEntityAxis = lnt_WplMember | 29.5 us-gaap_OtherAmortizationOfDeferredCharges / dei_LegalEntityAxis = lnt_WplMember | 43.7 us-gaap_OtherAmortizationOfDeferredCharges / dei_LegalEntityAxis = lnt_WplMember
Deferred tax expense (benefit) and investment tax credits | 80.7 us-gaap_DeferredIncomeTaxesAndTaxCredits / dei_LegalEntityAxis = lnt_WplMember | 86.5 us-gaap_DeferredIncomeTaxesAndTaxCredits / dei_LegalEntityAxis = lnt_WplMember | 88.6 us-gaap_DeferredIncomeTaxesAndTaxCredits / dei_LegalEntityAxis = lnt_WplMember
Equity (income) loss from unconsolidated investments, net | (42.8)us-gaap_IncomeLossFromEquityMethodInvestments / dei_LegalEntityAxis = lnt_WplMember | (43.7)us-gaap_IncomeLossFromEquityMethodInvestments / dei_LegalEntityAxis = lnt_WplMember | (42.1)us-gaap_IncomeLossFromEquityMethodInvestments / dei_LegalEntityAxis = lnt_WplMember
Distributions from equity method investments | 36.4 us-gaap_EquityMethodInvestmentDividendsOrDistributions / dei_LegalEntityAxis = lnt_WplMember | 35.4 us-gaap_EquityMethodInvestmentDividendsOrDistributions / dei_LegalEntityAxis = lnt_WplMember | 34.2 us-gaap_EquityMethodInvestmentDividendsOrDistributions / dei_LegalEntityAxis = lnt_WplMember
Equity component of allowance for funds used during construction | (6.0)us-gaap_IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction / dei_LegalEntityAxis = lnt_WplMember | (6.5)us-gaap_IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction / dei_LegalEntityAxis = lnt_WplMember | (8.9)us-gaap_IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction / dei_LegalEntityAxis = lnt_WplMember
Other | (1.2)us-gaap_OtherNoncashIncomeExpense / dei_LegalEntityAxis = lnt_WplMember | (0.2)us-gaap_OtherNoncashIncomeExpense / dei_LegalEntityAxis = lnt_WplMember | (2.9)us-gaap_OtherNoncashIncomeExpense / dei_LegalEntityAxis = lnt_WplMember
Other changes in assets and liabilities: |  |  |
Regulatory assets | (166.9)us-gaap_IncreaseDecreaseInOtherRegulatoryAssets / dei_LegalEntityAxis = lnt_WplMember | 69.1 us-gaap_IncreaseDecreaseInOtherRegulatoryAssets / dei_LegalEntityAxis = lnt_WplMember | (49.1)us-gaap_IncreaseDecreaseInOtherRegulatoryAssets / dei_LegalEntityAxis = lnt_WplMember
Regulatory liabilities | 29.7 us-gaap_IncreaseDecreaseInRegulatoryLiabilities / dei_LegalEntityAxis = lnt_WplMember | (8.5)us-gaap_IncreaseDecreaseInRegulatoryLiabilities / dei_LegalEntityAxis = lnt_WplMember | 28.5 us-gaap_IncreaseDecreaseInRegulatoryLiabilities / dei_LegalEntityAxis = lnt_WplMember
Accrued taxes | 0.1 us-gaap_IncreaseDecreaseInAccruedTaxesPayable / dei_LegalEntityAxis = lnt_WplMember | (26.9)us-gaap_IncreaseDecreaseInAccruedTaxesPayable / dei_LegalEntityAxis = lnt_WplMember | 19.2 us-gaap_IncreaseDecreaseInAccruedTaxesPayable / dei_LegalEntityAxis = lnt_WplMember
Pension and other benefit obligations | 92.0 us-gaap_IncreaseDecreaseInPensionAndPostretirementObligations / dei_LegalEntityAxis = lnt_WplMember | (71.3)us-gaap_IncreaseDecreaseInPensionAndPostretirementObligations / dei_LegalEntityAxis = lnt_WplMember | 31.7 us-gaap_IncreaseDecreaseInPensionAndPostretirementObligations / dei_LegalEntityAxis = lnt_WplMember
Other | (6.9)us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet / dei_LegalEntityAxis = lnt_WplMember | 10.2 us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet / dei_LegalEntityAxis = lnt_WplMember | (22.1)us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet / dei_LegalEntityAxis = lnt_WplMember
Net cash flows from operating activities | 424.4 us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = lnt_WplMember | 423.3 us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = lnt_WplMember | 427.4 us-gaap_NetCashProvidedByUsedInOperatingActivities / dei_LegalEntityAxis = lnt_WplMember
Cash flows used for investing activities: |  |  |
Utility business - purchase of Riverside Energy Center | 0 lnt_PaymentsToAcquireProductiveAssetsBusinessLine1 / dei_LegalEntityAxis = lnt_WplMember | 0 lnt_PaymentsToAcquireProductiveAssetsBusinessLine1 / dei_LegalEntityAxis = lnt_WplMember | (403.5)lnt_PaymentsToAcquireProductiveAssetsBusinessLine1 / dei_LegalEntityAxis = lnt_WplMember
Utility business - other | (312.9)lnt_PaymentsToAcquireProductiveAssetsOther / dei_LegalEntityAxis = lnt_WplMember | (331.4)lnt_PaymentsToAcquireProductiveAssetsOther / dei_LegalEntityAxis = lnt_WplMember | (314.5)lnt_PaymentsToAcquireProductiveAssetsOther / dei_LegalEntityAxis = lnt_WplMember
Other | (7.2)us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = lnt_WplMember | (4.5)us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = lnt_WplMember | 7.8 us-gaap_PaymentsForProceedsFromOtherInvestingActivities / dei_LegalEntityAxis = lnt_WplMember
Net cash flows used for investing activities | (320.1)us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = lnt_WplMember | (335.9)us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = lnt_WplMember | (710.2)us-gaap_NetCashProvidedByUsedInInvestingActivities / dei_LegalEntityAxis = lnt_WplMember
Cash flows from (used for) financing activities: |  |  |
Common stock dividends | (118.7)us-gaap_PaymentsOfDividendsCommonStock / dei_LegalEntityAxis = lnt_WplMember | (116.3)us-gaap_PaymentsOfDividendsCommonStock / dei_LegalEntityAxis = lnt_WplMember | (112.0)us-gaap_PaymentsOfDividendsCommonStock / dei_LegalEntityAxis = lnt_WplMember
Preferred dividends paid by subsidiaries | 0 us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock / dei_LegalEntityAxis = lnt_WplMember | (0.6)us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock / dei_LegalEntityAxis = lnt_WplMember | (3.3)us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock / dei_LegalEntityAxis = lnt_WplMember
Capital contributions from parent | 0 us-gaap_ProceedsFromContributionsFromParent / dei_LegalEntityAxis = lnt_WplMember | 0 us-gaap_ProceedsFromContributionsFromParent / dei_LegalEntityAxis = lnt_WplMember | 90.0 us-gaap_ProceedsFromContributionsFromParent / dei_LegalEntityAxis = lnt_WplMember
Payments to redeem cumulative preferred stock | 0 us-gaap_PaymentsForRepurchaseOfRedeemablePreferredStock / dei_LegalEntityAxis = lnt_WplMember | (61.0)us-gaap_PaymentsForRepurchaseOfRedeemablePreferredStock / dei_LegalEntityAxis = lnt_WplMember | 0 us-gaap_PaymentsForRepurchaseOfRedeemablePreferredStock / dei_LegalEntityAxis = lnt_WplMember
Proceeds from issuance of long-term debt | 250.0 us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = lnt_WplMember | 0 us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = lnt_WplMember | 250.0 us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = lnt_WplMember
Net change in commercial paper | (183.7)us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = lnt_WplMember | 97.1 us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = lnt_WplMember | 60.9 us-gaap_ProceedsFromRepaymentsOfShortTermDebt / dei_LegalEntityAxis = lnt_WplMember
Other | (5.7)us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = lnt_WplMember | (6.8)us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = lnt_WplMember | (4.8)us-gaap_ProceedsFromPaymentsForOtherFinancingActivities / dei_LegalEntityAxis = lnt_WplMember
Net cash flows from (used for) financing activities | (58.1)us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = lnt_WplMember | (87.6)us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = lnt_WplMember | 280.8 us-gaap_NetCashProvidedByUsedInFinancingActivities / dei_LegalEntityAxis = lnt_WplMember
Net increase (decrease) in cash and cash equivalents | 46.2 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = lnt_WplMember | (0.2)us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = lnt_WplMember | (2.0)us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease / dei_LegalEntityAxis = lnt_WplMember
Cash and cash equivalents at beginning of period | 0.5 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = lnt_WplMember | 0.7 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = lnt_WplMember | 2.7 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = lnt_WplMember
Cash and cash equivalents at end of period | 46.7 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = lnt_WplMember | 0.5 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = lnt_WplMember | 0.7 us-gaap_CashAndCashEquivalentsAtCarryingValue / dei_LegalEntityAxis = lnt_WplMember
Supplemental cash flows information: |  |  |
Interest, net of capitalized interest | (84.6)us-gaap_InterestPaidNet / dei_LegalEntityAxis = lnt_WplMember | (85.0)us-gaap_InterestPaidNet / dei_LegalEntityAxis = lnt_WplMember | (79.5)us-gaap_InterestPaidNet / dei_LegalEntityAxis = lnt_WplMember
Income taxes, net | (12.2)us-gaap_IncomeTaxesPaidNet / dei_LegalEntityAxis = lnt_WplMember | (22.9)us-gaap_IncomeTaxesPaidNet / dei_LegalEntityAxis = lnt_WplMember | 3.3 us-gaap_IncomeTaxesPaidNet / dei_LegalEntityAxis = lnt_WplMember
Significant non-cash investing and financing activities: |  |  |
Accrued capital expenditures | $ 38.4 us-gaap_CapitalExpendituresIncurredButNotYetPaid / dei_LegalEntityAxis = lnt_WplMember | $ 37.7 us-gaap_CapitalExpendituresIncurredButNotYetPaid / dei_LegalEntityAxis = lnt_WplMember | $ 39.5 us-gaap_CapitalExpendituresIncurredButNotYetPaid / dei_LegalEntityAxis = lnt_WplMember

X
- Definition The current period expense charged against earnings on long-lived, physical assets used in the normal conduct of business and not intended for resale to allocate or recognize the cost of assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset; amounts include discontinued operations. + References No definition available. + Details
Name: | lnt_AdjustmentDepreciationAndAmortizationIncludingDiscontinuedOperations
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The current period expense charged against earnings on long-lived, physical assets used in the normal conduct of business and not intended for resale to allocate or recognize the cost of assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset. + References No definition available. + Details
Name: | lnt_DepreciationAndAmortizationCashFlow
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The cash outflow for purchases of and capital improvements on property, plant and equipment (capital expenditures), software, and other intangible assets for the utility business. + References No definition available. + Details
Name: | lnt_PaymentsToAcquireProductiveAssetsBusinessLine1
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The cash outflow for purchases of and capital improvements on property, plant and equipment (capital expenditures), software, and other intangible assets for Alliant Energy Corporate Services, Inc. and non-regulated business. + References No definition available. + Details
Name: | lnt_PaymentsToAcquireProductiveAssetsBusinessLine2
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Payments To Acquire Productive Assets, Other + References No definition available. + Details
Name: | lnt_PaymentsToAcquireProductiveAssetsOther
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Proceeds from cash grant + References No definition available. + Details
Name: | lnt_ProceedsFromCashGrant
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

X
- Definition Future cash outflow to pay for purchases of fixed assets that have occurred. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4332-108586 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4313-108586 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586 + Details
Name: | us-gaap_CapitalExpendituresIncurredButNotYetPaid
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash -URI http://asc.fasb.org/extlink&oid=6506951 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash Equivalents -URI http://asc.fasb.org/extlink&oid=6507016 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 1 -Article 5 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.1) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=28358313&loc=d3e6676-107765 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3044-108585 + Details
Name: | us-gaap_CashAndCashEquivalentsAtCarryingValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of increase (decrease) in cash and cash equivalents. Cash and cash equivalents are the amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Includes effect from exchange rate changes. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 24 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3521-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 230 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6450594&loc=d3e33268-110906 + Details
Name: | us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

X
- Definition Amount of deferred income tax expense (benefit) and income tax credits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 20 -Section 55 -Paragraph 24 -URI http://asc.fasb.org/extlink&oid=32706628&loc=d3e11374-113907 + Details
Name: | us-gaap_DeferredIncomeTaxesAndTaxCredits
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition This item represents disclosure of the amount of dividends or other distributions received from unconsolidated subsidiaries, certain corporate joint ventures, and certain noncontrolled corporation; these investments are accounted for under the equity method of accounting. This element excludes distributions that constitute a return of investment, which are classified as investing activities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 13 -Article 5 + Details
Name: | us-gaap_EquityMethodInvestmentDividendsOrDistributions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition This item represents the entity's proportionate share for the period of the net income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. This item includes income or expense related to stock-based compensation based on the investor's grant of stock to employees of an equity method investee. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 9 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35755396&loc=d3e33749-111570 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.12) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 11 -Article 7 + Details
Name: | us-gaap_IncomeLossFromEquityMethodInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income, net of any cash received during the current period as refunds for the overpayment of taxes. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4297-108586 + Details
Name: | us-gaap_IncomeTaxesPaidNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The increase (decrease) during the reporting period in amount due within one year (or one business cycle) from customers for the credit sale of goods and services. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
Name: | us-gaap_IncreaseDecreaseInAccountsReceivable
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The increase (decrease) during the reporting period of all taxes owed but not paid, including income, property and other taxes. + References No definition available. + Details
Name: | us-gaap_IncreaseDecreaseInAccruedTaxesPayable
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The increase (decrease) during the reporting period in the capitalized cost of equity (based on assumed rate of return) and / or borrowed funds (based on interest rate) used to finance construction of regulated assets, which is expected to be recovered through rate adjustments. As a result of this capitalization, net income is increased. This element pertains to certain regulated industries, such as public utilities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
Name: | us-gaap_IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The increase (decrease) during the reporting period in the account that represents the temporary difference that results from Income or Loss that is recognized for accounting purposes but not for tax purposes and vice versa. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
Name: | us-gaap_IncreaseDecreaseInDeferredIncomeTaxes
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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

X
- Definition The increase (decrease) during the reporting period in other assets used in operating activities less other operating liabilities used in operating activities not separately disclosed in the statement of cash flows. May include changes in other current assets and liabilities, other noncurrent assets and liabilities, or a combination of other current and noncurrent assets and liabilities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
Name: | us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The increase (decrease) during the reporting period in other amounts due to the reporting entity, which are not otherwise defined in the taxonomy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
Name: | us-gaap_IncreaseDecreaseInOtherReceivables
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The increase (decrease) during the reporting period in the value of other assets that are created when regulatory agencies permits public utilities to defer costs to the balance sheet. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
Name: | us-gaap_IncreaseDecreaseInOtherRegulatoryAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The increase (decrease) during the reporting period in the amount due to fund pension and non-pension benefits to employees, retired and disabled former employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
Name: | us-gaap_IncreaseDecreaseInPensionAndPostretirementObligations
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The increase (decrease) during the reporting period in regulated liabilities. Regulated liabilities are created when regulatory agency permits an entity to defer revenues to the balance sheet. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
Name: | us-gaap_IncreaseDecreaseInRegulatoryLiabilities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The amount of cash paid for interest during the period net of cash paid for interest that is capitalized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4297-108586 + Details
Name: | us-gaap_InterestPaidNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of cash inflow (outflow) from financing activities, including discontinued operations. Financing activity cash flows include obtaining resources from owners and providing them with a return on, and a return of, their investment; borrowing money and repaying amounts borrowed, or settling the obligation; and obtaining and paying for other resources obtained from creditors on long-term credit. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 24 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3521-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 26 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3574-108585 + Details
Name: | us-gaap_NetCashProvidedByUsedInFinancingActivities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

X
- Definition Amount of cash inflow (outflow) from investing activities, including discontinued operations. Investing activity cash flows include making and collecting loans and acquiring and disposing of debt or equity instruments and property, plant, and equipment and other productive assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 24 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3521-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 26 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3574-108585 + Details
Name: | us-gaap_NetCashProvidedByUsedInInvestingActivities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

X
- Definition Amount of cash inflow (outflow) from operating activities, including discontinued operations. Operating activity cash flows include transactions, adjustments, and changes in value not defined as investing or financing activities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 24 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3521-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 25 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3536-108585 + Details
Name: | us-gaap_NetCashProvidedByUsedInOperatingActivities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

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

X
- Definition The portion of profit or loss for the period, net of income taxes, which is attributable to the parent. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Other Comprehensive Income -URI http://asc.fasb.org/extlink&oid=6519514 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Net Income -URI http://asc.fasb.org/extlink&oid=6518256 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.19) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.18) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.22) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 19 -Article 5 Reference 9: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 20 -Article 9 + Details
Name: | us-gaap_NetIncomeLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of amortization of other deferred costs recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.3) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 + Details
Name: | us-gaap_OtherAmortizationOfDeferredCharges
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Other income (expense) included in net income that results in no cash inflows or outflows in the period. Includes noncash adjustments to reconcile net income (loss) to cash provided by (used in) operating activities that are not separately disclosed. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
Name: | us-gaap_OtherNoncashIncomeExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The net cash outflow or inflow from other investing activities. This element is used when there is not a more specific and appropriate element in the taxonomy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3095-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3098-108585 + Details
Name: | us-gaap_PaymentsForProceedsFromOtherInvestingActivities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The cash outflow for reacquisition of callable preferred stock. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3291-108585 + Details
Name: | us-gaap_PaymentsForRepurchaseOfRedeemablePreferredStock
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of cash outflow in the form of ordinary dividends to common shareholders of the parent entity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3291-108585 + Details
Name: | us-gaap_PaymentsOfDividendsCommonStock
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of cash outflow in the form of ordinary dividends to preferred shareholders of the parent entity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3291-108585 + Details
Name: | us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The cash inflow from parent as a source of financing that is recorded as additional paid in capital. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3255-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 + Details
Name: | us-gaap_ProceedsFromContributionsFromParent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3255-108585 + Details
Name: | us-gaap_ProceedsFromIssuanceOfLongTermDebt
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The cash inflow from issuance of preferred stock that is classified as callable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3255-108585 + Details
Name: | us-gaap_ProceedsFromIssuanceOfRedeemablePreferredStock
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The net cash inflow or outflow from other financing activities. This element is used when there is not a more specific and appropriate element in the taxonomy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3095-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3098-108585 + Details
Name: | us-gaap_ProceedsFromPaymentsForOtherFinancingActivities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The net cash inflow or outflow for borrowing having initial term of repayment 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 -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 9 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3098-108585 + Details
Name: | us-gaap_ProceedsFromRepaymentsOfShortTermDebt
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3291-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 + Details
Name: | us-gaap_RepaymentsOfLongTermDebt
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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

X
- Details
Name: | dei_LegalEntityAxis=lnt_IplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=lnt_WplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |