Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Notional Amount of Derivatives [Table]
Schedule of Notional Amount of Derivatives [Table]
Schedule of Notional Amount of Derivatives [Table]
Instrument [Axis]
Energy [Axis]
Instrument Type [Domain]
Energy [Domain]
Electricity (MWhs) [Member]
Electricity Mwhs [Member]
Electricity (MWhs) [Member]
FTRs (MWhs) [Member]
Ftrs Mwhs [Member]
Ftrs Mwhs [Member]
Natural Gas (Dths) [Member]
Natural Gas Dths [Member]
Natural Gas (Dths) [Member]
Coal (Tons) [Member]
Coal Tons [Member]
Coal Tons [Member]
Diesel Fuel (Gallons) [Member]
Fuel [Member]
Trading Activity, by Type [Axis]
Trading Activity [Axis]
Trading Activity, by Type [Domain]
Trading Activity, by Type [Domain]
Commodity [Member]
Commodity [Member]
Legal Entity [Axis]
Legal Entity [Axis]
Entity [Domain]
Entity [Domain]
IPL [Member]
Ipl [Member]
IPL [Member]
WPL [Member]
Wpl [Member]
WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Amount of Derivatives [Line Items]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)
Derivative, Nonmonetary Notional Amount, Energy Measure
Notional unit amount of derivatives (in Dths)
Derivative, Nonmonetary Notional Amount
Notional unit amount of derivatives (in Tons)
Derivative, Nonmonetary Notional Amount, Mass
Notional unit amount of derivatives (in Gallons)
Derivative, Nonmonetary Notional Amount, Volume
Statement of Cash Flows [Abstract]
Statement [Table]
Statement [Table]
Statement [Line Items]
Statement [Line Items]
Cash flows from (used for) operating activities:
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income
Net Income (Loss) Attributable to Parent
Adjustments to reconcile net income to net cash flows from (used for) operating activities:
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Depreciation and amortization
Adjustment Depreciation And Amortization Including Discontinued Operations
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.
Depreciation and amortization
Depreciation and amortization, cash flow
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.
Deferred tax expense and tax credits
Deferred Income Taxes and Tax Credits
Equity income from unconsolidated investments, net
Income (Loss) from Equity Method Investments
Other
Other Noncash Income (Expense)
Other changes in assets and liabilities:
Increase (Decrease) in Operating Capital [Abstract]
Accounts receivable
Increase (Decrease) in Accounts Receivable
Regulatory assets
Increase (Decrease) in Other Regulatory Assets
Accounts payable
Increase (Decrease) in Accounts Payable
Regulatory liabilities
Increase (Decrease) in Regulatory Liabilities
Deferred income taxes
Increase (Decrease) in Deferred Income Taxes
Other
Increase (Decrease) in Other Operating Assets and Liabilities, Net
Net cash flows from (used for) operating activities
Net Cash Provided by (Used in) Operating Activities
Cash flows from (used for) investing activities:
Net Cash Provided by (Used in) Investing Activities [Abstract]
Utility business construction and acquisition expenditures
Payments To Acquire Productive Assets Business Line1
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.
Other construction and acquisition expenditures
Payments To Acquire Productive Assets Business Line2
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.
Cash receipts on sold receivables
Proceeds from Collection of Retained Interest in Securitized Receivables
Other
Payments for (Proceeds from) Other Investing Activities
Net cash flows from (used for) investing activities
Net Cash Provided by (Used in) Investing Activities
Cash flows from financing activities:
Net Cash Provided by (Used in) Financing Activities [Abstract]
Common stock dividends
Payments of Ordinary Dividends, Common Stock
Capital contributions from parent
Proceeds from Contributions from Parent
Proceeds from issuance of common stock, net
Proceeds from Issuance of Common Stock
Proceeds from issuance of long-term debt
Proceeds from Issuance of Long-term Debt
Payments to retire long-term debt
Repayments of Long-term Debt
Net change in commercial paper and other short-term borrowings
Proceeds from (Repayments of) Short-term Debt
Other
Proceeds from (Payments for) Other Financing Activities
Net cash flows from financing activities
Net Cash Provided by (Used in) Financing Activities
Net increase (decrease) in cash, cash equivalents and restricted cash
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect
Cash, cash equivalents and restricted cash at beginning of period
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations
Cash, cash equivalents and restricted cash at end of period
Supplemental cash flows information:
Supplemental Cash Flow Information [Abstract]
Interest, net of capitalized interest
Interest Paid, Net
Income taxes, net
Income Taxes Paid, Net
Significant non-cash investing and financing activities:
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Accrued capital expenditures
Capital Expenditures Incurred but Not yet Paid
Beneficial interest obtained in exchange for securitized accounts receivable
Consideration Received for Beneficial Interest Obtained for Transferring Financial Asset
Related Party Transactions [Abstract]
Schedule of Related Party Transactions, by Related Party [Table]
Schedule of Related Party Transactions, by Related Party [Table]
Related Party Transaction [Axis]
Related Party Transaction [Axis]
Related Party Transaction [Domain]
Related Party Transaction [Domain]
Administrative and General Services Billings [Member]
Administrative and General Services Billings [Member]
Administrative and General Services Billings [Member]
Sales Credited [Member]
Transmission Sales Credited [Member]
Transmission Sales Credited [Member]
Purchases Billed [Member]
Transmission Purchases Billed [Member]
Transmission Purchases Billed [Member]
Counterparty Name [Axis]
Counterparty Name [Axis]
Counterparty Name [Domain]
Counterparty Name [Domain]
Corporate Services [Member]
Corporate Services [Member]
Corporate Services [Member]
Related Party Transactions, by Related Party [Axis]
Related Party [Axis]
Related Party [Domain]
Related Party [Domain]
Subsidiary of Common Parent [Member]
Subsidiary of Common Parent [Member]
Related Party Transactions [Line Items]
Related Party Transaction [Line Items]
Amounts billed between related parties
Related Party Transaction, Amounts of Transaction
Accounting Policies [Abstract]
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligations [Table]
Asset Retirement Obligations [Table]
Asset Retirement Obligations [Table]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Receivables [Abstract]
Schedule of Accounts, Notes, Loans and Financing Receivable [Table]
Schedule of Accounts, Notes, Loans and Financing Receivable [Table]
Receivables [Line Items]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum And Average Outstanding Cash Proceeds
Schedule Of Sales Of Accounts Receivable Cash Proceeds And Related Costs Table Text Block
Schedule of maximum and average sales of accounts receivable cash proceeds and related costs.
Receivables Sold Under The Receivables Agreement
Schedule of Sales Of Accounts Receivable Sold Under Agreement Table Text Block
Schedule of sales of accounts receivable sold under Agreement.
Additional Attributes Of Receivables Sold Under The Receivables Agreement
Schedule of Additional Attributes of Receivables Sold Under the Agreement [Table Text Block]
Schedule of Additional Attributes of Receivables Sold Under the Agreement [Table Text Block]
Retirement Benefits [Abstract]
Benefit Plans
Compensation and Employee Benefit Plans [Text Block]
Investments [Abstract]
Schedule of Equity Method Investments [Table]
Schedule of Equity Method Investments [Table]
Schedule of Investments [Line Items]
Schedule of Equity Method Investments [Line Items]
Investments
Investment Holdings [Text Block]
New Accounting Pronouncements or Change in Accounting Principle [Table]
New Accounting Pronouncements or Change in Accounting Principle [Table]
Alliant Energy and IPL [Member]
Alliant Energy And Ipl [Member]
Alliant Energy And IPL
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adjustment to net periodic benefit costs, percentage
Adjustment To Net Periodic Benefit Costs, Percentage
Adjustment To Net Periodic Benefit Costs, Percentage
Income statement impact of adoption of Accounting Standards Update 2017-17
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Operating Results
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment [Table]
Schedule of Segment Reporting Information, by Segment [Table]
Segment Reporting Information [Line Items]
Segment Reporting Information [Line Items]
Segments Of Business
Segment Reporting Disclosure [Text Block]
Net amounts owed
Related Party Transaction, Due from (to) Related Party
Schedule of Defined Benefit Plans Disclosures [Table]
Schedule of Defined Benefit Plans Disclosures [Table]
Award Date [Axis]
Award Date [Axis]
Award Date [Domain]
Award Date [Domain]
2018 Grant [Member]
Two Thousand Eighteen [Member]
Two Thousand Eighteen [Member]
2017 Grant [Member]
Two Thousand Seventeen [Member]
Two Thousand Seventeen [Member]
2016 Grant [Member]
Two Thousand Sixteen [Member]
Two Thousand Sixteen [Member]
Award Type [Axis]
Award Type [Axis]
Award Type [Domain]
Equity Award [Domain]
Performance Shares [Member]
Performance Shares [Member]
Performance Units [Member]
Performance Units [Member]
Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number
Estimated payout percentage based on performance criteria
Estimated Payout Percentage
Estimated Payout Percentage
Fair values of each nonvested award (in dollars per share)
Employee Service Share Based Compensation Fair Values Of Each Nonvested Awards
Employee Service Share Based Compensation Fair Values Of Each Nonvested Awards
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue [Table]
Disaggregation of Revenue [Table]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer
Revenue from Contract with Customer [Text Block]
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments [Table]
Schedule of Long-term Debt Instruments [Table]
Debt [Line Items]
Debt Instrument [Line Items]
Commercial paper outstanding
Commercial Paper
Commercial paper weighted average interest rates
Short-term Debt, Weighted Average Interest Rate, at Point in Time
Available credit facility capacity
Line of Credit Facility, Remaining Borrowing Capacity
Public Utilities, General Disclosures [Abstract]
Retail Request [Table]
Retail Request [Table]
Retail Request [Table]
Regulatory Asset [Axis]
Regulatory Asset [Axis]
Regulatory Asset [Domain]
Regulatory Asset [Domain]
Net Book Value of ML Kapp [Member]
Net Book Value of ML Kapp [Member]
Net Book Value of ML Kapp [Member]
Income Tax Authority [Axis]
Income Tax Authority [Axis]
Income Tax Authority [Domain]
Income Tax Authority [Domain]
State [Member]
State and Local Jurisdiction [Member]
Regulatory Liability [Axis]
Regulatory Liability [Axis]
Regulatory Liability [Domain]
Regulatory Liability [Domain]
Revenue Subject to Refund [Member]
Revenue Subject to Refund [Member]
Deferral [Member]
Deferral [Member]
Deferral [Member]
Subsequent Event Type [Axis]
Subsequent Event Type [Axis]
Subsequent Event Type [Domain]
Subsequent Event Type [Domain]
Subsequent Event [Member]
Subsequent Event [Member]
Scenario [Axis]
Scenario [Axis]
Scenario, Unspecified [Domain]
Scenario, Unspecified [Domain]
Scenario, Forecast [Member]
Scenario, Forecast [Member]
Public Utilities, Regulatory Proceeding [Axis]
Public Utilities, Regulatory Proceeding [Axis]
Public Utilities, Regulatory Proceeding [Domain]
Public Utilities, Regulatory Proceeding [Domain]
Iowa tax reform [Member]
Iowa Tax Reform [Member]
Iowa Tax Reform [Member]
2017 and 2018 Test Period Retail Electric and Gas [Member]
Two Thousand Seventeen and Eighteen Test Period Retail Electric and Gas [Member]
Two Thousand Seventeen and Eighteen Test Retail Electric and Gas [Member]
2017 Test Year Retail Gas [Member]
Two Thousand Seventeen Test Year Retail Gas [Member]
Two Thousand Seventeen Test Year Retail Gas [Member]
2016 Test Year Retail Electric [Member]
Two Thousand Sixteen Test Year Retail Electric [Member]
Two Thousand Sixteen Test Year Retail Electric [Member]
Alliant Energy and WPL [Member]
Alliant Energy And Wpl [Member]
Alliant Energy And WPL
Regulatory Matters [Line Items]
Regulatory Matters [Line Items]
Regulatory Matters [Line Items]
State income tax rate
Effective Income Tax Rate Reconciliation, Percent
Decrease in regulatory assets
Increase in regulatory liabilities
Regulatory assets
Regulatory Assets
Regulatory liabilities
Regulatory Liabilities
Refunded Federal Tax Reform benefits
Deferred Revenue, Refund Payments
Requested rate increase, amount
Public Utilities, Requested Rate Increase (Decrease), Amount
Requested rate increase, percent
Public Utilities, Requested Rate Increase (Decrease), Percentage
Interim rate increase, amount
Public Utilities, Interim Rate Increase (Decrease), Amount
Interim rate increase, percent
Public Utilities, Interim Rate Increase (Decrease), Percentage
Approved rate increase, amount
Public Utilities, Approved Rate Increase (Decrease), Amount
Approved rate increase, percent
Public Utilities, Approved Rate Increase (Decrease), Percentage
Increase in base rates
Increase In Base Rates
Increase In Base Rates
Retirement Plan Type [Axis]
Retirement Plan Type [Axis]
Retirement Plan Type [Domain]
Retirement Plan Type [Domain]
Defined benefit pension plans [Member]
Pension Plan [Member]
OPEB Plans [Member]
Other Postretirement Benefits Plan [Member]
Service cost
Defined Benefit Plan, Service Cost
Interest cost
Defined Benefit Plan, Interest Cost
Expected return on plan assets
Defined Benefit Plan, Expected Return (Loss) on Plan Assets
Amortization of prior service credit
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)
Amortization of actuarial loss
Defined Benefit Plan, Amortization of Gain (Loss)
Total
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies Disclosure
Commitments and Contingencies Disclosure [Text Block]
Income Tax Disclosure [Abstract]
Income Taxes [Table]
Income Tax [Table]
Income tax
Income Taxes [Line Items]
Income Tax [Line Items]
Income tax
Schedule Of Effective Income Tax Rates
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]
Summary Of Tax Credit Carryforwards
Summary of Tax Credit Carryforwards [Table Text Block]
Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table]
Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table]
Derivative Instruments, Gain (Loss) by Derivative Instrument Risk [Axis]
Derivative Instrument [Axis]
Derivative Contract Type [Domain]
Derivative Contract [Domain]
Commodity Contracts [Member]
Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivatives, Fair Value [Line Items]
Current derivative assets
Derivative Asset, Current
Non-current derivative assets
Derivative Asset, Noncurrent
Current derivative liabilities
Derivative Liability, Current
Non-current derivative liabilities
Derivative Liability, Noncurrent
Regulated Operations [Abstract]
Discontinued Operations and Disposal Groups [Abstract]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Table]
Disposal Groups, Including Discontinued Operations [Table]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
ATC Billings To WPL [Member]
Atc Billings To Wpl [Member]
ATC billings to WPL [Member]
WPL Billings To ATC [Member]
Wpl Billings To Atc [Member]
WPL billings to ATC [Member]
ATC [Member]
American Transmission Company Llc Atc [Member]
American Transmission Company LLC (ATC) [Member]
Equity Method Investee [Member]
Equity Method Investee [Member]
Range [Axis]
Range [Axis]
Range [Domain]
Range [Domain]
Minimum [Member]
Minimum [Member]
Maximum [Member]
Maximum [Member]
Receivable Type [Axis]
Receivable Type [Axis]
Receivable [Domain]
Receivable [Domain]
Receivables Sold [Member]
Receivables Sold [Member]
Receivables Sold
Limit on cash proceeds
Trade Receivables Held-for-sale, Amount
Available capacity
Sale of Accounts Receivable Program, Capacity Available
Sale of Accounts Receivable Program, Capacity Available
Outstanding receivables past due
Outstanding receivables past due
Outstanding receivables past due
Debt
Debt Disclosure [Text Block]
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment [Table]
Property, Plant and Equipment [Table]
Property, Plant and Equipment, Type [Axis]
Property, Plant and Equipment, Type [Axis]
Property, Plant and Equipment, Type [Domain]
Property, Plant and Equipment, Type [Domain]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment [Line Items]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block]
Schedule Of Segments Of Business
Schedule of Segment Reporting Information, by Segment [Table Text Block]
Fair Value Disclosures [Abstract]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table]
Excluding Financial Transmission Rights [Member]
Excluding Financial Transmission Rights [Member]
Excluding Financial Transmission Rights [Member]
Financial Transmission Rights [Member]
Financial Transmission Rights [Member]
Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, by Asset Type [Axis]
Asset Class [Axis]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Asset Types [Domain]
Asset Class [Domain]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value
Fair value, net derivative liabilities
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value
Stockholders' Equity Note [Abstract]
Common Equity [Table]
Common Equity [Table]
Common Equity [Table]
Sale of Stock [Axis]
Sale of Stock [Axis]
Sale of Stock [Domain]
Sale of Stock [Domain]
At The Market Offering Program [Member]
At The Market Offering Program [Member]
At The Market Offering Program [Member]
Common Equity [Line Items]
Common Equity [Line Items]
Common Equity [Line Items]
Common Stock Oustanding [Roll Forward]
Common Stock Oustanding [Roll Forward]
Common Stock Oustanding [Roll Forward]
Shares outstanding, January 1, 2018 (in shares)
Common Stock, Shares, Outstanding
At-the-market offering program (in shares)
Stock Issued During Period, Shares, New Issues
Shareowner Direct Plan issuances (in shares)
Shares Of Stock Issued Shareowner Direct Plan
Shares Of Stock Issued Shareowner Direct Plan
Equity-based compensation plans (in shares)
Stock Issued During Period, Shares, Employee Stock Purchase Plans
Other (in shares)
Other Common Stock Activity
Other Common Stock Activity
Shares outstanding, June 30, 2018 (in shares)
Statement of Financial Position [Abstract]
ASSETS
Assets [Abstract]
Current assets:
Assets, Current [Abstract]
Cash and cash equivalents
Cash and Cash Equivalents, at Carrying Value
Accounts receivable, less allowance for doubtful accounts
Accounts Receivable, Net, Current
Production fuel, at weighted average cost
Energy Related Inventory, Other Fossil Fuel
Gas stored underground, at weighted average cost
Energy Related Inventory, Gas Stored Underground
Materials and supplies, at weighted average cost
Inventory, Raw Materials and Supplies, Gross
Regulatory assets
Regulatory Assets, Current
Other
Other Assets, Current
Total current assets
Assets, Current
Property, plant and equipment, net
Property, Plant and Equipment, Net
Investments:
Long-term Investments [Abstract]
ATC Holdings
Investments Business Line 1
Carrying amount as of the balance sheet date of investment in American Transmission Company LLC.
Other
Other Long-term Investments
Total investments
Long-term Investments
Other assets:
Other Assets, Noncurrent [Abstract]
Regulatory assets
Regulatory Assets, Noncurrent
Deferred charges and other
Other Assets, Noncurrent
Total other assets
Assets, Noncurrent
Total assets
Assets
LIABILITIES AND EQUITY
Liabilities and Equity [Abstract]
Current liabilities:
Liabilities, Current [Abstract]
Current maturities of long-term debt
Long-term Debt, Current Maturities
Commercial paper
Other short-term borrowings
Other Short-term Borrowings
Accounts payable
Accounts Payable, Current
Regulatory liabilities
Regulatory Liability, Current
Other
Other Liabilities, Current
Total current liabilities
Liabilities, Current
Long-term debt, net (excluding current portion)
Long-term Debt, Excluding Current Maturities
Other liabilities:
Deferred Credits and Other Liabilities [Abstract]
Deferred tax liabilities
Deferred Tax Liabilities, Net, Noncurrent
Regulatory liabilities
Regulatory Liability, Noncurrent
Capital lease obligations - Sheboygan Falls Energy Facility
Capital Lease Obligations, Noncurrent
Pension and other benefit obligations
Liability, Defined Benefit Plan, Noncurrent
Other
Other Liabilities, Noncurrent
Total other liabilities
Deferred Credits and Other Liabilities
Commitments and contingencies (Note 13)
Commitments and Contingencies
Equity:
Capitalization, Long-term Debt and Equity [Abstract]
Common equity:
Stockholders' Equity Attributable to Parent [Abstract]
Common stock
Common Stock, Value, Issued
Additional paid-in capital
Additional Paid in Capital, Common Stock
Retained earnings
Retained Earnings (Accumulated Deficit)
Accumulated other comprehensive income (loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax
Shares in deferred compensation trust - 465,450 and 463,365 shares at a weighted average cost of $24.47 and $23.91 per share
Common Stock Held in Trust
Total common equity
Stockholders' Equity Attributable to Parent
Cumulative preferred stock of Interstate Power and Light Company
Noncontrolling Interest, Amount Represented by Preferred Stock
Total equity
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest
Total liabilities and equity
Liabilities and Equity
Long-term Purchase Commitment [Table]
Long-term Purchase Commitment [Table]
Long-term Purchase Commitment by Category of Item Purchased [Axis]
Category of Item Purchased [Axis]
Long-term Purchase Commitment, Category of Item Purchased [Domain]
Long-term Purchase Commitment, Category of Item Purchased [Domain]
Manufactured Gas Plant Sites [Member]
Natural Gas Processing Plant [Member]
Commitments and Contingencies [Line Items]
Long-term Purchase Commitment [Line Items]
Minimum range of estimated future costs
Minimum Remaining Estimated Cost Incurred for Investigation, Remediation and Monitoring
Minimum Remaining Estimated Cost Incurred for Investigation, Remediation and Monitoring
Maximum range of estimated future costs
Maximum Remaining Estimated Cost Incurred for Investigation, Remediation and Monitoring
Maximum Remaining Estimated Cost Incurred for Investigation, Remediation and Monitoring
Current and non-current environmental liabilities
Accrual for Environmental Loss Contingencies
Schedule of Asset Retirement Obligations [Line Items]
Schedule of Asset Retirement Obligations [Line Items]
[Line Items] for Schedule of Asset Retirement Obligations [Table]
Derivative [Table]
Derivative [Table]
Derivative Instruments [Line Items]
Derivative [Line Items]
Notional Amounts Of Derivative Instruments
Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block]
Fair Value Of Financial Instruments
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]
Common stock, par value
Common Stock, Par or Stated Value Per Share
Common stock, shares authorized (in shares)
Common Stock, Shares Authorized
Common stock, shares outstanding (in shares)
Shares in deferred compensation trust (in shares)
Common Stock Held In Trust Shares
Total number of common stock shares held in trust.
Shares in deferred compensation trust, weighted average cost per share (in dollars per share)
Common Stock Held In Trust Weighted Average Value Per Share
Weighted average value per share; generally not indicative of the fair market value per share.
Receivables
Loans, Notes, Trade and Other Receivables Disclosure [Text Block]
Income Taxes
Income Tax Disclosure [Text Block]
Segments [Axis]
Segments [Axis]
Segments [Domain]
Segments [Domain]
Electric [Member]
Electric [Member]
Electric [Member]
Gas [Member]
Gas [Member]
Gas [Member]
Other Utility [Member]
Other Utility [Member]
Other Utility [Member]
Non-utility and Other [Member]
Other Segments [Member]
Customer [Axis]
Customer [Axis]
Customer [Domain]
Customer [Domain]
Retail - residential [Member]
Retail - Residential [Member]
Retail - Residential [Member]
Retail - commercial [Member]
Retail - Commercial [Member]
Retail - Commercial [Member]
Retail - industrial [Member]
Retail - Industrial [Member]
Retail - Industrial [Member]
Wholesale [Member]
Wholesale [Member]
Wholesale [Member]
Steam [Member]
Steam [Member]
Steam [Member]
Other [Member]
Other Customer [Member]
Other Customer [Member]
Transportation and other [Member]
Transportation and Other [Member]
Transportation and Other [Member]
Revenue from contracts with customers
Revenue from Contract with Customer, Excluding Assessed Tax
Effective Tax Rate [Table]
Effective Tax Rate [Table]
Effective tax rate
Effective Tax Rate [Line Items]
Effective Tax Rate [Line Items]
Effective tax rate
Statutory federal income tax rate
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent
State income taxes, net of federal benefits
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent
Effect of rate-making on property-related differences
Effective Income Tax Rate Reconciliation Effect Of Rate Making On Property Related Differences
Effective Income Tax Rate Reconciliation Effect Of Rate Making On Property Related Differences
Production tax credits
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Percent
IPL's tax benefit riders
Effective Income Tax Rate Reconciliation Tax Benefit Rider
Effective income tax rate reconciliation tax benefit rider
Other items, net
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent
Overall income tax rate
Fair Value, by Balance Sheet Grouping [Table]
Fair Value, by Balance Sheet Grouping [Table]
Statement [Line Items]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Measurements
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]
Fair Value Measurements Using Significant Unobservable Inputs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]
Fair Value Of Net Derivative Assets (Liabilities)
Net Derivative Assets And Liabilities [Table Text Block]
Net Derivative Assets And Liabilities [Table Text Block]
Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table]
Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table]
2015 Grant [Member]
Two Thousand Fifteen Grant [Member]
Two Thousand Fifteen Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Nonvested, January 1 (in shares/awards)
Granted (in shares/awards)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period
Vested (in shares/awards)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period
Forfeited (in shares/awards)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period
Nonvested, June 30 (in shares/awards)
Vested percentage of the target
Vested Percentage Of The Target
Vested Percentage Of The Target
Aggregate payout value
Employee Benefits and Share-based Compensation
Payout - cash
Employee Service Share-based Compensation, Cash Flow Effect, Cash Used to Settle Awards
Payout - common stock shares issued (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period
Investments [Table]
Investment [Table]
Investment, Name [Axis]
Investment, Name [Axis]
Investment, Name [Domain]
Investment, Name [Domain]
Non-utility wind farm In Oklahoma [Member]
Non-utility Wind Investment In Oklahoma [Member]
Non-utility Wind Investment In Oklahoma [Member]
Schedule of Investments [Line Items]
Investment [Line Items]
Equity (income) loss from unconsolidated investments, net
Compensation expense
Allocated Share-based Compensation Expense
Income tax benefits
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense
ATC Holdings [Member]
Investment In Atc [Member]
Investment In ATC [Member]
Other [Member]
Other Equity Method Investments [Member]
Other Equity Method Investments [Member]
Public Utility Regulated or Unregulated Status [Axis]
Regulation Status [Axis]
Regulated and Unregulated Operation [Domain]
Regulated and Unregulated Operation [Domain]
Non-Utility [Member]
Unregulated Operation [Member]
Utility Business [Member]
Utility Business [Member]
Utility Business [Member]
ATC Holdings, Non-Utility, Parent and Other [Member]
Revenues
Revenues
Operating income (loss)
Operating Income (Loss)
Income from continuing operations, net of tax
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent
Income from discontinued operations, net of tax
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest
Net income attributable to common shareowners
Net Income (Loss) Available to Common Stockholders, Basic
Increase (decrease) in deferred tax liabilities
Increase Decrease In Deferred Income Taxes Noncurrent Liabilities
Increase Decrease In Deferred Income Taxes Noncurrent Liabilities
Operating Loss Carryforwards [Table]
Operating Loss Carryforwards [Table]
Operating Loss Carryforwards by Tax Authority [Axis]
Federal [Member]
Domestic Tax Authority [Member]
Carryforwards [Line Items]
Operating Loss Carryforwards [Line Items]
Net operating losses, carryforward amount
Operating Loss Carryforwards
Tax credits, carryforward amount
Tax Credit Carryforward, Amount
Maximum amount outstanding (based on daily outstanding balances)
Short-term Debt, Maximum Amount Outstanding During Period
Average amount outstanding (based on daily outstanding balances)
Short-term Debt, Average Outstanding Amount
Weighted average interest rates
Weighted Average Interest Rate Short Term Debt
Reflects the calculation as of the balance sheet date of the average interest rate weighted by the amount of short-term debt outstanding by type or by instrument at that time.
Guarantor Obligations, Nature [Axis]
Guarantor Obligations, Nature [Axis]
Guarantor Obligations, Nature [Domain]
Guarantor Obligations, Nature [Domain]
Indemnification Agreement [Member]
Indemnification Agreement [Member]
Capital Purchase Obligation [Member]
Capital Purchase Obligation [Member]
Capital Purchase Obligation [Member]
Purchased Power [Member]
Purchased Power [Member]
Purchased Power [Member]
Minimum future commitments
Long-term Purchase Commitment, Amount
Present value abandonment obligation
Present value abandonment obligation
Present value abandonment obligation
Indemnification obligations, maximum
Guarantor Obligations, Maximum Exposure, Undiscounted
Property, Plant and Equipment
Property, Plant and Equipment Disclosure [Text Block]
Common Share Activity
Schedule of Capital Units [Table Text Block]
General, Basis of Accounting
Basis of Accounting, Policy [Policy Text Block]
General, Use of Estimates
Use of Estimates, Policy [Policy Text Block]
General, Reclassification
Reclassification, Policy [Policy Text Block]
Cash, Cash Equivalents and Restricted Cash
Cash and Cash Equivalents, Policy [Policy Text Block]
Revenue Recognition
Revenue Recognition, Policy [Policy Text Block]
New Accounting Standards
New Accounting Pronouncements, Policy [Policy Text Block]
Maximum aggregate gross sales price of common stock that can be offered and sold
Maximum Aggregate Gross Sales Price Of Common Stock That Can Be Offered And Sold
Maximum Aggregate Gross Sales Price Of Common Stock That Can Be Offered And Sold
Common stock issued during the period, At-the-market offering program (in shares)
Fees and commissions from issuance of common stock
Fees And Commissions From Issuance Of Common Stock
Fees And Commissions From Issuance Of Common Stock
Retained earnings free of dividend restrictions
Retained Earnings, Unappropriated
Restricted net assets of subsidiaries
Amount of Restricted Net Assets for Consolidated and Unconsolidated Subsidiaries
Comprehensive income
Other Comprehensive Income (Loss), Net of Tax
Deferred Proceeds [Member]
Deferred Proceeds Of Receivables Sold [Member]
Deferred Proceeds Of Receivables Sold [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance
Total net gains (losses) included in changes in net assets (realized/unrealized)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings
Transfers out of Level 3
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3
Purchases
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases
Sales
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales
Settlements
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements
Ending balance
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at June 30
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)
Public Utilities General Disclosures [Table]
Public Utilities General Disclosures [Table]
Public Utilities, General Disclosures [Line Items]
Public Utilities, General Disclosures [Line Items]
Regulatory Matters
Public Utilities Disclosure [Text Block]
Income Statement [Abstract]
Revenues:
Revenues [Abstract]
Electric utility
Electric Domestic Regulated Revenue
Gas utility
Gas Domestic Regulated Revenue
Other utility
Other Revenue, Net
Non-utility
Unregulated Operating Revenue
Total revenues
Operating expenses:
Costs and Expenses [Abstract]
Electric production fuel and purchased power
Electric Production Expense
Electric transmission service
Cost of Transmission
Cost of gas sold
Cost of Domestic Regulated Gas Revenue
Other operation and maintenance
Other Cost and Expense, Operating
Other operation and maintenance
Utilities Operating Expense, Maintenance and Operations
Depreciation and amortization
Depreciation, Depletion and Amortization, Nonproduction
Taxes other than income taxes
Taxes, Miscellaneous
Total operating expenses
Costs and Expenses
Operating income
Other (income) and deductions:
Nonoperating Income (Expense) [Abstract]
Interest expense
Interest Expense
Allowance for funds used during construction
Public Utilities, Allowance for Funds Used During Construction, Additions
Other
Other Nonoperating Income (Expense)
Total other (income) and deductions
Nonoperating Income (Expense)
Income tax expense (benefit)
Income Tax Expense (Benefit)
Income from continuing operations, net of tax
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest
Net income
Preferred dividend requirements of Interstate Power and Light Company
Dividends, Preferred Stock
Net income attributable to common shareowners
Weighted average number of common shares outstanding (basic and diluted) (in shares)
Weighted Average Number of Shares Outstanding, Basic and Diluted
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted):
Earnings Per Share, Basic and Diluted [Abstract]
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted) (in dollars per share)
Earnings Per Share, Basic and Diluted
Amounts attributable to common shareowners:
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest [Abstract]
Income from continuing operations, net of tax
Income from discontinued operations, net of tax
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent
Net income attributable to common shareowners
Dividends declared per common share (in dollars per share)
Common Stock, Dividends, Per Share, Declared
Public Utility [Axis]
Public Utility [Axis]
Utility Plant [Domain]
Utility Plant [Domain]
West Riverside Energy Center [Member]
West Riverside Energy Center [Member]
West Riverside Energy Center [Member]
Expansion of Wind Generation [Member]
Expansion of Wind Generation Project [Member]
Expansion of Wind Generation Project [Member]
Fossil-fueled EGU capacity (in megawatts)
Fossil Fueled Energy Generating Units Capacity
Fossil Fueled Energy Generating Units Capacity
Construction work in progress
Public Utilities, Property, Plant and Equipment, Construction Work in Progress
Allowance for funds used during construction
Fossil-fueled EGU capacity acquired by electric cooperatives (in megawatts)
Fossil Fueled Energy Generating Units Capacity Acquired by Electric Cooperatives
Fossil Fueled Energy Generating Units Capacity Acquired by Electric Cooperatives
Wholesale power supply agreement, term of extension
Wholesale Power Supply Agreement, Term Of Extension
Wholesale Power Supply Agreement, Term Of Extension
Wholesale power supply agreement, term of notice requirement
Wholesale Power Supply Agreement, Term of Notice Requirement
Wholesale Power Supply Agreement, Term of Notice Requirement
Electric capacity of wind farm (in megawatts)
Electric Capacity Of Wind Project
Electric Capacity Of Wind Project
Estimated fair value of net assets acquired
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net
Outstanding aggregate cash proceeds (based on daily outstanding balances)
Proceeds from Sale and Collection of Receivables
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table]
Measurement Basis [Axis]
Measurement Basis [Axis]
Fair Value Measurement [Domain]
Fair Value Measurement [Domain]
Fair Value [Member]
Portion at Fair Value Measurement [Member]
Carrying Amount [Member]
Reported Value Measurement [Member]
Fair Value, Hierarchy [Axis]
Fair Value, Hierarchy [Axis]
Fair Value Hierarchy [Domain]
Fair Value Hierarchy [Domain]
Level 1 [Member]
Fair Value, Inputs, Level 1 [Member]
Level 2 [Member]
Fair Value, Inputs, Level 2 [Member]
Level 3 [Member]
Fair Value, Inputs, Level 3 [Member]
Assets:
Derivatives
Derivative Asset
Deferred proceeds
Deferred proceeds of receivables sold
Deferred proceeds of receivables sold
Deferred proceeds
Fair value of deferred proceeds of receivables sold
Fair value of deferred proceeds of receivables sold
Liabilities and Equity:
Capitalization and liabilities [Abstract]
Capitalization and liabilities [Abstract]
Derivatives
Derivative Liability
Long-term debt (incl. current maturities)
Long-term Debt
Long-term debt (incl. current maturities)
Long-term Debt, Fair Value
Cumulative preferred stock of IPL
Preferred Stock, Value, Issued
Cumulative preferred stock of IPL
Preferred Stock Fair Value
Preferred Stock Fair Value
Long-term Debt, Type [Axis]
Long-term Debt, Type [Axis]
Long-term Debt, Type [Domain]
Long-term Debt, Type [Domain]
Term Loan Credit Agreement [Member]
Term Loan Credit Agreement [Member]
Term Loan Credit Agreement [Member]
Senior Notes [Member]
Senior Notes [Member]
Debt Instrument [Axis]
Debt Instrument [Axis]
Debt Instrument, Name [Domain]
Debt Instrument, Name [Domain]
Short-term loan credit agreement through 2018 [Member]
Short Term Loan Credit Agreement Through Two Thousand Eighteen [Member] [Member]
Short Term Loan Credit Agreement Through Two Thousand Eighteen [Member] [Member]
Term loan credit agreement through April 2020 [Member]
Term Loan Credit Agreement Through April Two Thousand and Twenty [Member]
Term Loan Credit Agreement Through April Two Thousand and Twenty [Member]
3.75% senior notes due 2023 [Member]
Three point seven five senior notes due two thousand and twenty three [Member]
Three Point Seven Five Senior Notes Due Two Thousand And Twenty Three [Member]
4.25% senior notes due 2028 [Member]
Four Point Two Five Percent Senior Notes Due Two Thousand And Twenty Eight [Member]
Four Point Two Five Percent Senior Notes Due Two Thousand And Twenty Eight [Member]
Term loan credit agreement through 2018 [Member]
Term Loan Credit Agreement Through Two Thousand Eighteen [Member]
Term Loan Credit Agreement Through Two Thousand Eighteen [Member]
Alliant Energy Finance LLC [Member]
Alliant Energy Finance LLC [Member]
Alliant Energy Finance LLC [Member]
Retirement of debt
Repayments of Debt
Proceeds from issuance of long-term debt
Proceeds from Issuance of Debt
Variable-rate term loan, interest rate
Debt Instrument, Interest Rate, Stated Percentage
Commercial paper, long-term
Long-term Commercial Paper
Commercial paper, long-term, weighted average interest rate
Long-term Debt, Weighted Average Interest Rate, at Point in Time
Disposal Group Name [Axis]
Disposal Group Name [Axis]
Disposal Groups, Including Discontinued Operations, Name [Domain]
Disposal Group Name [Domain]
Performance Restricted Stock Unit [Member]
Performance Restricted Stock Unit [Member]
Performance Restricted Stock Unit [Member]
Restricted Stock Units [Member]
Restricted Stock Units (RSUs) [Member]
Nonvested, January 1, weighted average grant date fair value (in dollars per share)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value
Granted, weighted average grant date fair value (in dollars per share)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value
Forfeited, weighted average grant date fair value (in dollars per share)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value
Nonvested, June 30, weighted average grant date fair value (in dollars per share)
Other Purchase Obligations
Long-Term Purchase Commitment, Operating Expenses Purchase Obligation [Table Text Block]
Long-Term Purchase Commitment, Operating Expenses Purchase Obligation [Table Text Block]
MGP Site Estimated Future Costs And Recorded Liabilities
Environmental Exit Costs by Cost [Table Text Block]
Unrecognized compensation cost
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized
Unrecognized compensation cost recognized over a weighted average period
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition
Alliant Energy common stock closing price on June 29, 2018 (in dollars per share)
Common Stock Closing Price
Common Stock Closing Price
Schedule of Regulatory Assets [Table]
Schedule of Regulatory Assets [Table]
Tax-related [Member]
Tax Related [Member]
Tax Related [Member]
Pension and OPEB costs [Member]
Pension and Other Postretirement Plans Costs [Member]
Asset retirement obligations [Member]
Asset Retirement Obligation Costs [Member]
EGUs retired early [Member]
Electric Generating Units Retired Early [Member] [Member]
Electric Generating Units Retired Early [Member]
Derivatives [Member]
Deferred Derivative Gain (Loss) [Member]
Emission allowances [Member]
Emission Allowances [Member]
Emission Allowances [Member]
Other [Member]
Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets [Line Items]
Fair Value Measurements
Fair Value Disclosures [Text Block]
Common Equity
Stockholders' Equity Note Disclosure [Text Block]
Debt Disclosure [Table]
Debt Disclosure [Table]
Debt Disclosure [Table] [Table]
Debt Disclosure [Line Items]
Debt Disclosure [Line Items]
[Line Items] for Debt Disclosure [Table] [Table]
Other Short-Term Borrowings
Schedule of Short-term Debt [Table Text Block]
Unconsolidated Equity Investments
Equity Method Investments [Table Text Block]
Document And Entity Information [Abstract]
Document and Entity Information [Abstract]
Entity Registrant Name
Entity Registrant Name
Entity Central Index Key
Entity Central Index Key
Current Fiscal Year End Date
Current Fiscal Year End Date
Entity Filer Category
Entity Filer Category
Entity Common Stock, Shares Outstanding
Entity Common Stock, Shares Outstanding
Document Fiscal Year Focus
Document Fiscal Year Focus
Document Fiscal Period Focus
Document Fiscal Period Focus
Document Type
Document Type
Amendment Flag
Amendment Flag
Document Period End Date
Document Period End Date
Disaggregation of Revenue
Disaggregation of Revenue [Table Text Block]
Derivative Instruments
Derivative Instruments and Hedging Activities Disclosure [Text Block]
Performance Shares and Performance Units [Member]
Performance Shares and Units [Member]
Performance Shares and Units [Member]
Restricted Stock Unit [Member]
Restricted Stock Unit And Restricted Unit [Member]
Restricted Stock Unit And Restricted Unit [Member]
Defined Benefit Pension And Other Postretirement Benefits Plans
Schedule of Net Benefit Costs [Table Text Block]
Recognized Compensation Expense And Income Tax Benefits
Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block]
Schedule Of Equity-based Compensation Plans Activity
Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block]
Long-term Contract for Purchase of Electric Power [Axis]
Long-term Contract for Purchase of Electric Power [Axis]
Long-term Contract for Purchase of Electric Power [Domain]
Long-term Contract for Purchase of Electric Power [Domain]
DAEC PPA [Member]
DAEC PPA [Member]
DAEC PPA [Member]
Natural gas [Member]
Public Utilities, Inventory, Natural Gas [Member]
Coal [Member]
Coal Supply Agreements [Member]
Other [Member]
Long-term Purchase Commitments, Other [Member]
Long-term Purchase Commitments, Other [Member]
PPA term amendment
Long-term Contract for Purchase of Electric Power, Contract Term Amendment
Long-term Contract for Purchase of Electric Power, Contract Term Amendment
PPA buyout payment
Long-term Contract for Purchase of Electric Power, Buyout Payment
Long-term Contract for Purchase of Electric Power, Buyout Payment
Individual commitments incurred
Individual Commitments Incurred
Individual commitments incurred in excess of $1 million
Customer accounts receivable
Customer Accounts Receivable Sold, Amount
Customer Accounts Receivable Sold, Amount
Unbilled utility revenues
Unbilled Utility Revenues Sold, Amount
Unbilled Utility Revenues Sold, Amount
Other receivables
Other Receivables Sold Amount
Other Receivables Sold Amount
Receivables sold to third party
Receivables sold
Receivables sold
Less: cash proceeds
Cash Proceeds From Receivables Sold
Cash Proceeds From Receivables Sold
Deferred proceeds
Less: allowance for doubtful accounts
Allowance for Doubtful Accounts Receivable Sold
Allowance for Doubtful Accounts Receivable Sold
Fair value of deferred proceeds
Estimated fair value of property, plant and equipment, net purchased
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment
Estimated fair value of liabilities assumed
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities
Related Parties
Related Party Transactions Disclosure [Text Block]
WPL Owed ATC LLC [Member]
Wpl Owed Atc [Member]
WPL owed ATC [Member]
Services Provided, Sales Credited And Purchases
Schedule Of Scoa Sales Credited And Purchases Billed [Table Text Block]
Schedule of System Coordination and Operating Agreement Schedule of Sales Credited and Purchases Billed (Table Text Block)
Net Intercompany Payables
Schedule of Corporate Services Intercompany Payables [Table Text Block]
Schedule of Corporate Services Intercompany Payables (Table Text Block).
Related Amounts Billed Between Parties
Schedule Of ATC Billings Table Text Block
Schedule of amounts billed for ATC (Table Text Block)
Schedule of Regulatory Liabilities [Table]
Schedule of Regulatory Liabilities [Table]
Cost of removal obligations [Member]
Removal Costs [Member]
Electric transmission cost recovery [Member]
Electric Transmission Cost Recovery [Member]
Electric Transmission Cost Recovery [Member]
Commodity cost recovery [Member]
Commodity Cost Recovery [Member]
Commodity Cost Recovery [Member]
IPL's tax benefit riders [Member]
Ipl S Tax Benefit Rider [Member]
IPL's Tax Benefit Rider [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities [Line Items]
Summary Of Significant Accounting Policies
Significant Accounting Policies [Text Block]
Regulatory Assets
Schedule of Regulatory Assets [Table Text Block]
Regulatory Liabilities
Schedule of Regulatory Liabilities [Table Text Block]
Collections
Collections Reinvested In Receivables
Collections reinvested related to sales of accounts receivable program.
Write-offs, net of recoveries
Credit losses, net of recoveries
Credit losses, net of recoveries related to sales of accounts receivable program.