Preferred stock, 5.00% Series This element represents the preferred stock with 5.00% dividend rate. Preferred Stock 5.00 Percent Series [Member] Preferred stock, 5.04% Series This element represents the preferred stock with 5.04% dividend rate. Preferred Stock 5.04 Percent Series [Member] Preferred stock, 5.08% Series This element represents the preferred stock with 5.08% dividend rate. Preferred Stock 5.08 Percent Series [Member] Preferred stock, 6.76% Series This element represents the preferred stock with 6.76% dividend rate. Preferred Stock 6.76 Percent Series [Member] Preferred stock, 6.88% Series This element represents the preferred stock with 6.88% dividend rate. Preferred Stock 6.88 Percent Series [Member] Long Term debt to parent, 8.76% Series, Year Due, 2015 This element represents the debt instrument issued to parent with 8.76% interest rate. Long Term Debt to Parent 8.76 Percent Series, Due 2015 [Member] Award Type [Axis] Long Term debt to parent, 7.35% Series, Year Due, 2016 This element represents the debt instrument issued to parent with 7.35% interest rate. Long Term Debt to Parent 7.35 Percent Series, Due 2016 [Member] Long Term debt, 7.125% Series, Year Due, 2023 This element represents the debt instrument issued with 7.125% interest rate. Long Term Debt 7.125 Percent Series, Due 2023 [Member] Long Term debt, 4.875% Series, Year Due, 2012 This element represents the debt instrument issued with 4.875% interest rate. Long Term Debt 4.875 Percent Series, Due 2012 [Member] Long Term debt, 3.95% Series, Year Due, 2013 This element represents the debt instrument issued with 3.95% interest rate. Long Term Debt 3.95 Percent Series, Due 2013 [Member] Amendment Description Long Term debt, 4.80% Series, Year Due, 2013 This element represents the debt instrument issued with 4.80% interest rate. Long Term Debt 4.80 Percent Series, Due 2013 [Member] Amendment Flag Long Term debt, 6.375% Series, Year Due, 2015 This element represents the debt instrument issued with 6.375% interest rate. Long Term Debt 6.375 Percent Series, Due 2015 [Member] Long Term debt, 5.65% Series, Year Due, 2017 This element represents the debt instrument issued with 5.65% interest rate. Long Term Debt 5.65 Percent Series, Due 2017 [Member] Long Term debt, 6.08% Series, Year Due, 2028 This element represents the debt instrument issued with 6.08% interest rate. Long Term Debt 6.08 Percent Series, Due 2028 [Member] Long Term debt, 5.55% Series, Year Due, 2036 This element represents the debt instrument issued with 5.55% interest rate. Long Term Debt 5.55 Percent Series, Due 2036 [Member] Regulatory Authority [Axis] This element represents regulatory authorities. Wisconsin [Member] Public Service Commission of Wisconsin (PSCW) Represents the Public Service Commission of Wisconsin (PSCW) which regulates the operations of WPS. Segregation of rate matters by phases in regulatory review of rate proposals. Rate Review Stages [Axis] Original Request [Member] Entity's Original Request The original request submitted to regulatory authorities for rate proposals. Regulatory Review Proceedings [Axis] Segregation of rate matters by the regulatory proceedings in which the entity is engaged. Retail Natural Gas Rate Request [Member] Represents information relating to retail natural gas rates. Natural gas rate case Year of Rate Cases [Axis] Year for which the rate cases are filed. Component of Other Income Expense Nonoperating [Axis] Group that contains each detailed component of other nonoperating income and expenses. Key Executive Life Insurance Income [Member] Key executive life insurance This element represents the income associated with key executive life insurance. Other Nonoperating Income (Expense) Other [Member] Other The net amount of other income and expense amounts, components of which are not separately disclosed in other nonoperating income or expense. Electric Utility [Member] Electric Utility Represents the Electric Utility segment which includes the regulated electric utility operations. Electric transactions Natural Gas Utility [Member] Natural Gas Utility Represents the Natural Gas Utility segment which includes the regulated natural gas utility operations. Natural gas transactions Current Fiscal Year End Date Commodity Contract Natural Gas [Member] Natural gas contracts Derivative instrument whose primary underlying risk is tied to the commodity price of natural gas. Commodity Contract Financial Transmission Rights [Member] FTRs Derivative instrument whose primary underlying risk is tied to the commodity price of financial transmission rights. Commodity Contract Petroleum Products [Member] Petroleum product contracts Derivative instrument whose primary underlying risk is tied to the commodity price of petroleum products. Derivatives Not Designated as Hedges Financial Statement Location [Axis] The location and amount of gains and losses reported in the statement of financial performance or the statement of financial position. Regulatory Assets Current [Member] Balance Sheet - Regulatory assets (current) Represents the line item on the balance sheet for current regulatory assets. Regulatory Assets Noncurrent [Member] Balance Sheet - Regulatory assets (long Term) The line item on the balance sheet for noncurrent regulatory assets. Regulatory Liability Current [Member] Balance Sheet - Regulatory liabilities (current) Represents the line item on the balance sheet for current regulatory liabilities. Cost of Fuel Natural Gas and Purchased Power [Member] Income Statement - Cost of fuel, natural gas and purchased power Represents the line item on the income statement for cost of fuel, natural gas and purchased power. Regulatory Liabilities Noncurrent [Member] Balance Sheet - Regulatory liabilities (long-term) The line item on the balance sheet for noncurrent regulatory liabilities. Derivative Activity [Axis] The grouping of types of activities for which the entity has derivative contracts. Derivative Purchases [Member] Purchases Represents derivative contracts related to purchases. Document Period End Date Derivative Other Transactions [Member] Other transactions Represents derivative contracts related to other transactions. Revolving Credit Facility Maturing 23, April 2013 [Member] Revolving credit facility maturing on April 23, 2013 Represents the revolving credit facility maturing on 23 April, 2013. Revolving Credit Facility Maturing 12, June 2013 [Member] Revolving credit facility maturing on June 12, 2013 Represents the revolving credit facility maturing on 12 June, 2013. Revolving Credit Facility Maturing 17 May, 2014 [Member] Revolving credit facility maturing on May 17, 2014 Represents the revolving credit facility maturing on May 17, 2014. Schedule of Purchase Supply Commitment [Axis] Information by arrangements, in which entity has agreed for purchase and supply obligation. Coal Supply and Transportation [Member] Coal supply and transportation Represents the obligation related to coal supply and transportation. Purchased Power [Member] Purchased Power Represents the obligation for either capacity or energy related to purchased power. Other Commodities [Member] Other commodities Represents the obligation related to other commodities. Natural Gas Supply and Transportation [Member] Natural Gas Supply and transportation Represents the committed obligation related to natural gas supply and transportation. Entity [Domain] Purchase Order [Member] Purchase orders Represents commitments in form of purchase orders that relate to normal business operations, including construction projects. Performance Stock Rights Equity Awards [Member] Performance Stock Rights accounted for as Equity awards Represents information pertaining to performance based equity awards. Performance Stock Rights Liability Award [Member] Performance Stock Rights accounted as Liability awards Represents information pertaining to performance based liability awards. Performance Stock Rights accounted for as Liability awards Restricted Shares and Restricted Share Units [Member] Restricted Shares and Restricted Share Units Represents shares or units for which sale is contractually or governmentally restricted for a given period of time. Restricted shares and restricted share units Retail Electric Rate Request [Member] Represents information relating to retail electric rates. Retail electric rate case Mercury Emission Reduction [Axis] Information by type of phases of reduction in mercury emission. E P A Settlements with Other Utilities [Member] EPA Settlements with Other Utilities Represents the information pertaining to EPA (Environmental Protection Agency) settlements with other utilities. Weston and Pulliam Plants [Member] Weston and Pulliam Plants Represents the information pertaining to the Weston and Pulliam plants. Pulliam Title V Air Permit [Member] Pulliam Title V Air Permit Represents the information pertaining to legal issues related to Pulliam Title V Air Permit. Mercury Emission [Member] Mercury emission Represents the information pertaining to mercury emission defined by the BACT rule. Sulfur Dioxide and Nitrogen Oxide Emissions Represents the information pertaining to sulfur dioxide and nitrogen oxide emissions defined by CAIR. Sulfur Dioxide and Nitrogen Oxide Emissions [Member] Manufactured Gas Plant Remediation [Member] Manufactured Gas Plant Remediation Represents the information pertaining to remediation relating to manufacturing and storing manufactured gas. Columbia Title V Air Permit [Member] Columbia Title V Air Permit Represents the information pertaining to columbia generation station air permit legal issues. Phase Two [Member] Phase II Represents information pertaining to Phase II of reduction in mercury emission. W D N R Issued N O Vs [Member] WDNR Issued NOV's Represents the information pertaining to notice of Violations issued by Wisconsin Department of Natural Resources. Regulatory Authorities Rate Order [Member] Rate Order Approved rate order by regulatory authorities. Phase One [Member] Phase I Represents information pertaining to Phase I of reduction in mercury emission. Pending Acquisition [Member] Pending purchase Represents information pertaining to a pending acquisition agreement. Document and Entity Information Carrying amount as of the balance sheet date of payments made in advance for income and other taxes which will be charged against earnings, and of income taxes previously overpaid to tax authorities (such as the U.S. federal, state and local tax authorities) representing refunds of overpayments or recoveries based on agreed-upon resolutions of disputes due within one year or the normal operating cycle, whichever is longer. Prepaid federal income tax and taxes receivable Prepaid Taxes and Taxes Receivable, Current Prepaid gross receipts tax Prepaid Gross Receipts Taxes Carrying amount as of the balance sheet date of payments made in advance for the gross receipts tax. Gross receipts tax is a revenue based tax, which is paid by the regulated utilities in lieu of general property taxes. Liabilities from risk management activities Represents the sum as of the balance sheet date of the (a) fair values of all liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments, and (b) the carrying amounts of the liabilities arising from financial instruments or contracts used to mitigate a specified risk (hedge), and which are expected to be extinguished or otherwise disposed of within a year or the normal operating cycle, if longer. Derivative Instruments and Hedges Liabilities, Gross, Current Other current liabilities from risk management activities Cost of Fuel Natural Gas and Purchased Power The amount of fuel, natural gas and purchased power charged against earnings for the period. Cost of fuel, natural gas, and purchased power CONDENSED CONSOLIDATED STATEMENTS OF CAPITALIZATION Long-term debt, 6.125% Series, Year Due, 2011 This element represents the debt instrument issued with 6.125% interest rate. Long Term Debt 6.125 Percent Series, Due 2011 [Member] Balance Common Stock Equity Total of all Stockholders' Equity items other than those pertaining to Preferred Stock. Includes the following: Common Stock at Par, Common Stock Additional Paid-in Capital, Retained Earnings, and Accumulated Other Comprehensive Income (Loss). Total common stock equity Balance Total First Mortgage Bonds and Senior Notes First Mortgage Bonds and Senior Notes This element represents the carrying value as of the balance sheet date of collateralized senior notes and first mortgage bonds. Recoveries and refunds of regulatory assets and liabilities Recoveries and Refunds of Regulatory Assets and Liabilities Recoveries of capitalized costs and refunds of liabilities (generally revenues and other gains) previously required to be recorded as regulatory assets and regulatory liabilities at the company's regulated entities. Prepaid federal income taxes and taxes receivable Increase (Decrease) in Prepaid Taxes and Taxes Receivable, Current The increase (decrease) during the reporting period in the amount of payments made in advance for income and other taxes, which will be charged against earnings in future periods and in income taxes receivable, which represents the amount due from tax authorities for refunds of overpayments or recoveries of income taxes paid. Refund of amounts previously paid by related parties for unfunded nonqualified retirement plan benefit costs. Amount repaid to related parties Payments for Refunds of Payments Received from Related Parties for Unfunded Retirement Benefit Costs Repayment of related party payable Net proceeds from equity method investee's sales of energy to MISO Proceeds from Related Party Sales Cash received from the sales made by equity method investees during the current period. Due from Related Parties Benefits Aggregate amount of receivables to be collected from related parties where one party can exercise control or significant influence over another party; including affiliates, owners or officers and their immediate families, pension trusts, and so forth, at the financial statement date. Amounts due relate to benefit costs. Benefit costs, Receivables from related parties Assets transferred to IBS Proceeds from Transfer of Pension Plan Obligations and Assets to Affiliates This element represents cash received from the transfer of pension plan obligations and assets to affiliates occurred in connection with the change in plan sponsor. Restricted Cash Used for Repayment of Long Term Debt This element represents restricted cash used for repayment of long term debt. Restricted cash for repayment of long-term debt Cash paid for transmission interconnection Payments for Transmission Interconnection The cash outflow associated with an interconnection agreement to fund the construction of transmission facilities. Proceeds received from transmission interconnection Proceeds Received from Transmission Interconnection The cash inflow associated with the reimbursement related to an interconnection agreement used to fund construction of transmission facilities. CASH AND CASH EQUIVALENTS Cash and Cash Equivalents and Cash Flow Supplemental Disclosure [Text Block] The entire disclosure of cash and cash equivalents. This may include short term investments, maturity details, and supplemental disclosure to statement of cash flow. SHORT-TERM DEBT AND LINES OF CREDIT SHORT-TERM DEBT AND LINES OF CREDIT Short Term Debt and Line of Credit Facilities Disclosure [Text Block] This element may be used as a single block of text to encapsulate the entire disclosure for short-term borrowings including data and tables. This element may be used to capture the complete disclosure pertaining to short-term or long-term contractual arrangements with lenders, including letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to maximum amounts as of any point in time conditional on satisfaction of specified terms before, as of, and after the date of drawdowns on the line. COMMON EQUITY Common Shareholders Equity [Text Block] Description of restrictions on dividend payments, financial capital structure requirements, dividends paid to parent, and return of capital to parent or equity contributions from parent. VARIABLE INTEREST ENTITIES Variable Interest Entities Disclosure [Text Block] VARIABLE INTEREST ENTITIES Disclosure of variable interest entities and transactions with these entities. Schedule of unrealized gains (losses) recorded related to derivatives Schedule of Other Derivatives Not Designated as Hedging Instruments Statements of Financial Performance and Financial Position Location Utility Segments [Table Text Block] Tabular disclosure for other derivative instruments not designated as hedging instruments of the utility segments of the entity of the location and amount of gains and losses reported in the statement of financial performance and in the statement of financial position. Schedule of notional volumes of outstanding derivative contracts Schedule of Notional Volumes of Outstanding Derivative Contracts [Table Text Block] Tabular disclosure of the notional amounts of outstanding derivative contracts. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Schedule of cash collateral positions Schedule of Derivative Instruments Cash Collateral Positions [Table Text Block] Tabular presentation of the cash collateral provided to others or received from others related to derivative assets and liabilities. Disclosure of average amount of short-term borrowings outstanding Tabular disclosure of average amount of short-term borrowings outstanding based on daily outstanding balances. Schedule of Average Amount of Short Term Borrowings Outstanding [Table Text Block] Entity Well-known Seasoned Issuer Schedule of Effective Income Tax Rate [Table Text Block] Schedule of effective tax rates Tabular disclosure of the current and prior period effective tax rates as compared to the federal statutory tax rate. Entity Voluntary Filers Schedule of Share Based Payment Award, Performance Stock Rights Valuation Assumptions [Table Text Block] Disclosure of performance stock rights assumptions Tabular disclosure of the significant assumptions used during the year to estimate the fair value of performance stock rights, including, but not limited to: (a) expected term, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. Entity Current Reporting Status Schedule of reconciliation of changes in the fair value of items categorized as Level 3 measurements Tabular disclosure of the fair value measurement of assets and liabilities using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes during the period. Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Table Text Block] Entity Filer Category Schedule of Other Nonoperating Income (Expense) by Component [Table Text Block] Schedule of total miscellaneous income Tabular disclosure of the detailed components of other nonoperating income and expenses. Entity Public Float Derivative Instruments and Hedges Liabilities Gross Noncurrent Other long-term liabilities from risk management activities Represents the sum as of the balance sheet date of the (a) fair values of all liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments, and (b) the carrying amounts of the liabilities arising from financial instruments or contracts used to mitigate a specified risk (hedge), and which are expected to be extinguished or otherwise disposed of after a year or beyond the normal operating cycle, if longer. Entity Registrant Name Financial Statement Location [Domain] The income statement and balance sheet location of gains and losses on derivative instruments not designated as hedging instruments. Entity Central Index Key Derivative Activity [Domain] The types of activities for which the entity has derivative contracts. Short Term Debt Average Discount Rate Average discount rate (as a percent) Represents the average discount rate applied to short-term debt. Ratio of Indebtedness to Net Capital in Percentage Debt to total capitalization ratio (as a percent) Percentage of total aggregate indebtedness divided by net capital. Entity Common Stock, Shares Outstanding Schedule of Purchase Supply Commitment [Table] Summarization of information required or determined to be disclosed about arrangements in which the entity has agreed to expend funds to procure goods or services from one or more suppliers and arrangements in which the entity has committed resources to supply goods or services to a customer. Purchase Supply Commitment [Domain] This item is intended to be populated, by the entity, with Members identifying each purchase commitment and supply commitment about which information required or determined to be disclosed is being provided. Purchase and Supply Commitment [Line Items] Purchase and sales commitments disclosure Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Long Term Supply Contracts Obligation Amount Supply contract obligation amount Represents the amount of a long-term commitment to supply goods or services to one or more customers. Mercury Emission Reduction by Phase [Domain] Type of phases of reduction in mercury emission. Represents the number of notice of violations (NOV) alleging various violations of the air permits received since 2008. Number of Notice of Violations of Air Permits Number of NOV's alleging violations of the air permits received since 2008 Represents the number of NOV's for clerical error received since 2008. Number of Notice of Violations for Clerical Error Number of NOV's for clerical error received since 2008 Corrective Actions Taken for Notice of Violations Issued Number of corrective actions taken for NOV's received Represents the number of corrective actions that have been taken related to NOV's received. Notice of Violations Dismissed Number NOV's dismissed Represents the number of NOV's dismissed. Minimum Number of Remedial Step Required Number of remedial steps required, minimum Represents the minimum number of remedial steps required to be completed if historical projects required a state or federal CAA permit. Notice of Violations Referred to State Justice Department Number of NOV's referred to the state Justice Department for enforcement Represents the number of NOV's referred to the state Justice Department for enforcement. E P A Review Period in Days Number of days which the EPA reviewed proposed permit Represents the period of time within which the EPA reviewed the proposed air permit, expressed in days. E P A Order Directed W D N R Resolve Objections within Period in Days Number of days which the EPA directed WDNR to resolve renewal objection Represents the period of time within which the EPA directed WDNR to resolve the EPA's objection to an air permit renewal, expressed in days. Percentage Mercury Emission Reduction Represents the percentage of mercury emission reduction required by BACT rule. Percentage mercury reduction required by Best Available Control Technology rule Mercury Emission Reduction for Electric Generating Units above 150 M W Level of electric generating units above which a 90% reduction in mercury emissions is required by 2015 (in MW) Represents electric generating units for which a 90% reduction in mercury emissions is required by 2015. Percentage Mercury Emission Reduction for Electric Generating Units Above 150 M W Percentage mercury reduction, required by Best Available Control Technology rule Represents the percentage of mercury emission reduction for electric generating units above 150 MW as required by BACT rule. Mercury Emission Reduction for Electric Generating Units Above 25 M W Level of electric generating units above which a reduction in mercury emissions (in MW) Percentage mercury reduction beginning year 2015, required by Best Available Control Technology rule. Document Fiscal Year Focus Estimated Environmental Capital Costs Estimated capital cost to achieve required emission reduction Represents estimated capital costs, including estimates for both wholly owned and jointly owned plants, to achieve the require level of reduction in mercury emissions. Document Fiscal Period Focus Number of States Included in C A I R Regulations Number of states included in the CAIR regulation Represents number of states included in the CAIR regulation. Number of Remediation Sites Number of environmental remediation sites Represents the number of sites for which the entity is responsible for environmental remediation. Number of Remediation Sites Transferred to E P A Super fund Alternative Sites Program Number of environmental remediation sites transferred to the EPA Superfund Alternative Sites Program Represents the number of sites that have been transferred to the EPA Superfund Alternative Sites Program. Represents the amount of the expected recovery of deferred expenditures and estimated future expenditures, net of insurance recoveries for remediation which the entity has recorded as regulatory assets. Regulatory Asset Recovery of Remediation Expenditures Regulatory assets recorded for cash and estimated future remediation expenditures, net of insurance recoveries received Insurance Recoveries Received Insurance recoveries received Represents insurance recoveries received. Defined Benefit Plan Regulatory Deferral Regulatory deferral Represents the amortization of the regulatory deferral of defined benefit plan costs. Share Based Compensation Arrangement by Share Based Payment Award, Fair Value Assumptions Period of Historical Volatility used to Estimate Expected Volatility Rate Period of historical volatility used to estimate expected volatility Represents the number of years used in estimating the expected stock price volatility during the reporting period. Share Based Compensation Arrangement by Share Based Payment Award, Options Weighted Average Remaining Contractual Term [Abstract] Weighted-Average Remaining Contractual Life (in Years) Share Based Compensation Arrangement by Share Based Payment Award, Options Aggregate Intrinsic Value [Abstract] Aggregate Intrinsic Value (Millions) Share Based Compensation Arrangement by Share Based Payment Award, Period Prior to End of Performance Period for which Employees Cannot Change Election to Defer Value of Award Into Deferred Compensation Plan Period prior to the end of the performance period during which employees cannot change their election to defer the value of award into deferred compensation plan Represents period prior to the end of the performance period during which employees cannot change their election to defer the value of award into deferred compensation plan. Represents the remaining performance period for which fair value on the modification date is used to measure the awards. Share Based Compensation Arrangement by Share Based Payment Award, Remaining Performance Period for which Fair Value on Plan Modification Date is used to Measure Awards Remaining performance period for which fair value on the modification date is used to measure the awards (in months) Legal Entity [Axis] Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other than Options Dividend Equivalent Dividend equivalents (in shares) Represents the number of equity-based payment instruments, excluding stock (or unit) options, that are dividend equivalent. Document Type Represents the number of shares (or other type of equity) adjusted for award modification during the period on other than stock (or unit) option plans. Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other than Options Award, Modification Award modifications (in shares) Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other than Options Distributed in Period Distributed (in shares) Represents the number of shares (or other type of equity) distributed during the period on other than stock (or unit) option plans. Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other than Options Adjustments in Period Adjustment for final payout (in shares) Represents the number of shares (or other type of equity) adjusted for to reflect that actual payout during the period on other than stock (or unit) option plans. Transfers (in shares) The number of equity-based payment instruments, excluding stock (or unit) options, that were transferred during the reporting period. Share Based Compensation Arrangement by Share Based Payment Award Equity Instruments Other than Options Transfers in Period Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other than Options Award Dividend Equivalent, Weighted Average Grant Date Fair Value Dividend equivalents (in dollars per shares) Represents the weighted-average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that are dividend equivalents. Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other than Options Distributed in Period, Total Intrinsic Value Total intrinsic value of awards vested Represents the total intrinsic value of equity-based payment equity instruments, excluding stock (or unit) options, distributed during the reporting period as calculated by applying the disclosed pricing methodology. Employee Service Share Based Compensation Tax Benefit Realized from Distribution of Shares Tax benefit realized from the distribution of shares Represents the aggregate tax benefit realized from the distribution of shares during the reporting period. Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other than Options Vested in Period, Total Intrinsic Value Total intrinsic value of awards vested Represents the total intrinsic value of equity-based payment equity instruments, excluding stock (or unit) options that vested during the reporting period as calculated by applying the disclosed pricing methodology. Tax benefit realized from the vesting of shares Represents the aggregate tax benefit realized from the vesting of shares during the reporting period. Employee Service Share Based Compensation Tax Benefit Realized from Vesting of Shares Schedule of Dividend Payment Restrictions [Table] Schedule itemizing dividend payment restrictions imposed by regulatory authorities. Regulatory Authority [Domain] This element represents regulatory authorities. Dividend Payment Restrictions [Line Items] Common Equity Percentage of Previous Period Dividend as Restriction on Current Period Dividends Percentage of previous period's dividend as restriction on current period dividends Represents the percentage of previous period's dividend as restriction on current period's dividends. Dividend Payment Restrictions Percentage of Common Stockholders Equity to Total Capitalization Percentage of common stockholders equity to total capitalization for dividend payment restrictions Represents the percentage of common stockholders equity to total capitalization for dividend payment restrictions. Dividend Payment Restrictions Debt to Capitalization Ratio Debt to capitalization ratio required to be maintained (as a percent) Represents the debt to capitalization ratio required to be maintained. Fair Value Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Table] Tabular disclosure of the information required and determined to be provided for purposes of reconciling beginning and ending balances of fair value measurements of assets and liabilities using significant unobservable inputs (level 3). Fair Value Inputs Assets and Liabilities Quantitative Information [Table] Schedule of the inputs used in the fair value measurement of assets and liabilities. This disclosure may include, but is not limited to, the fair value of the asset and liabilities, valuation technique used to measure fair value, the inputs used to measure fair value, the ranges of the inputs, and the weighted averages of the inputs. Fair Value Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items] Reconciliation for all assets and liabilities measured at estimated fair value Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation Calculation [Roll Forward] Fair Value Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation Calculation Roll forward of changes in the fair value of items categorized as Level 3 measurements for the period. Fair Value Measurement with Unobservable Inputs Reconciliation Recurring Basis Asset and Liability Value This element represents assets and liabilities measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances. Balance at the beginning of period Balance at the end of period Fair Value Measurement with Unobservable Inputs Reconciliation Recurring Basis Asset and Liability Gain (Loss) Included in Earnings Represents the total gains or losses for the period, arising from assets and liabilities measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings. Net realized (losses) gains included in earnings Fair Value Measurement with Unobservable Inputs Reconciliation Recurring Basis Asset and Liability Unrealized Losses Recorded as Regulatory Assets or Liabilities Represents the total unrealized gains or losses for the period, arising from assets and liabilities measured at fair value on a recurring basis using unobservable inputs (Level 3), which are recorded as regulatory assets or liabilities. Net unrealized gains (losses) recorded as regulatory assets or liabilities This element represents purchases during the period of assets and liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy. Purchases Fair Value Measurement with Unobservable Inputs Reconciliation Recurring Basis Asset and Liability Purchases This element represents sales during the period of assets and liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy. Sales Fair Value Measurement with Unobservable Inputs Reconciliation Recurring Basis Asset and Liability Sales Fair Value Measurement with Unobservable Inputs Reconciliation Recurring Basis Asset and Liability Settlements This element represents settlements during the period of assets and liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy. Settlements Component of Other Income Expense Nonoperating [Table] Provides a description and the amount of each detailed component of other nonoperating income and expenses. Component of Other Income Expense Nonoperating Name [Domain] Name of each detailed component of other nonoperating income and expenses. Accounts Payable, Current Accounts payable Component of Other Income Expense Nonoperating [Line Items] Components of miscellaneous income Schedule of Public Utilities Regulatory Matters [Table] Schedule of specific disclosures related to information that impacts rates and amortization of regulatory assets and liabilities. Regulatory Review Proceedings [Domain] The regulatory proceedings in which the entity is engaged. Rate Review Stages [Domain] The phases in regulatory review of rate proposals. Regulatory Authorities Interim Rate Order [Member] Interim Rate Order Approved interim rate order by regulatory authorities. Regulatory Environment [Line Items] Regulatory Proceedings: Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Requested Rate Increase (Decrease) in Revenue Rate Increase (decrease) Represents the amount of increase (decrease) to existing rates requested from the appropriate regulators. Requested Rate of Return on Common Equity Percent return on equity Represents the Rate of return on common equity requested from the appropriate regulators. Requested Percent of Capital Structure Composed of Equity Equity ratio percent Represents the ratio of equity to total capitalization (debt plus equity) requested from the appropriate regulators. Authorized Rate Increase (Decrease) in Revenue Rate increase (decrease) Represents the amount of increase (decrease) to existing rates. Recovery of Prior Deferrals Recovery of prior deferral Represents the amount of recovery of prior deferrals. Estimated Fuel Refund Estimated fuel refund Represents the estimated fuel refund including the carrying cost. Authorized Rate of Return on Common Equity Percent return on equity Represents the rate of return on common equity approved by the appropriate regulators. Authorized Rate of Return on Common Equity in Previous Order Authorized rate of return on common equity in the previous rate order (as a percent) Represents the rate of return on common equity approved by the appropriate regulators in the previous rate order. Authorized Percent of Capital Structure Composed of Equity Equity ratio percent Represents the ratio of equity to total capitalization (debt plus equity) approved by the appropriate regulators. Percentage of Price Variance from Cost of Fuel and Purchased Power Percentage of price variance from the cost of fuel and purchased power included in rates Represents the percentage of price variance from the cost of fuel and purchased power included in rates. Deferred Regulatory, Liability Deferred regulatory liability related to fuel and purchased power cost over-collections Represents the amount of deferred regulatory liability related to fuel and purchased power cost over-collections. JOINTLY OWNED UTILITY FACILITIES Jointly Owned Utility Facilities Disclosure [Text Block] JOINTLY OWNED UTILITY FACILITIES This element represents disclosure of proportionate interests in jointly owned utility plants. Include the amount of plants in service, the accumulated provision for depreciation (if available), the amount of plants under construction, and the proportionate share. Information concerning two or more generating plants on the same site may be combined. States that the utility's share of direct expenses of the joint plants is included in the corresponding operating expenses on its income statement (for example, fuel, maintenance of plant, other operating expense). If the share of direct expenses is charged to purchase power, then disclose the amount so charged and the proportionate amounts charged to specific operating expenses on the records maintained for the joint plants. PREFERRED STOCK Equity contribution from parent Net Equity Infusions from Parent This element represents the contributed capital from parent as a source of financing that is recorded as additional paid in capital. Net return of capital to parent Adjustments to Additional Paid in Capital Return of Capital to Parent Reduction to additional paid in capital resulting from a distribution of earnings to the parent company. Senior Notes 4.875, Percent Due in December 2012 [Member] 4.875% Senior Notes A contractual arrangement to repay the borrowed amount under senior notes at an interest rate of 4.875 percent, maturing in December, 2012 . A contractual arrangement to repay the borrowed amount under senior notes at an interest rate of 3.95 percent, maturing in February, 2013. Senior Notes 3.95, Percent Due in February 2013 [Member] 3.95% Senior Notes Defined Benefit Unfunded Non Qualified Plan Reduction in Pension Obligation Reduction in pension obligation Represents the amount of reduction made in the pension obligation under the unfunded non-qualified retirement plan. Transfers (in shares) Share Based Compensation Arrangement by Share Based Payment Award Options Transfers in Period Number of options or other stock instruments which are transferred during the period under the terms of the plan agreements. Transfers (in dollars per share) Share Based Compensation Arrangement by Share Based Payment Award Options Transfers in Period Weighted Average Grant Date, Fair Value The weighted average grant-date fair value of options transferred during the reporting period as calculated by applying the disclosed option pricing methodology. Share Based Compensation Arrangement by Share Based Payment Award Equity Instruments Other than Options Distributed Weighted Average Grant Date, Fair Value Distributed (in dollars per share) Weighted-average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were distributed during the period as per the agreement made under the plan. Adjustment for final payout (in dollars per share) Weighted-average fair value as of the grant date of equity-based award plans other than stock (unit) option plans for which adjustment for final payout was made as per the agreement made under the plan. Share Based Compensation Arrangement by Share Based Payment Award Equity Instruments Other than Options Adjustments Weighted Average Grant Date, Fair Value Share Based Compensation Arrangement by Share Based Payment Award Equity Instruments Other than Options Transfers Weighted Average Grant Date, Fair Value Transfers (in dollars per share) Weighted-average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were transferred during the period as per the agreement made under the plan. Significant internally-developed unobservable inputs used in the valuation of derivatives categorized in Level 3 Tabular disclosure of quantitative information about the inputs used in the fair value measurement of assets and liabilities. This disclosure may include, but is not limited to, the fair value of the asset and liabilities, valuation technique used to measure fair value, the inputs used to measure fair value, the ranges of the inputs, and the weighted averages of the inputs. Fair Value Inputs Assets and Liabilities Quantitative Information [Table Text Block] Fair Value Inputs Assets and Liabilities Quantitative Information [Line Items] Fair Value Inputs Assets and Liabilities Quantitative Information Fair Value Inputs Forward Market Prices Forward market prices (in dollars per megawatt or ton) The forward market price on the future contracts used as an input to measure fair value. Environmental Compliance Obligations [Abstract] Environmental Upper Peninsula Power Company [Member] Represents information pertaining to Upper Peninsula Power Company. UPPCO Represents information pertaining to American Transmission Company LLC. American Transmission Company L L C [Member] ATC Wisconsin River Power Company [Member] WRPC Represents information pertaining to Wisconsin River Power Company. Represents information pertaining to WPS Investments, LLC. W P S Investments L L C [Member] WPS Investments, LLC Schedule of Related Party Transactions Information [Table Text Block] Schedule of information related to transactions entered into with related parties Tabular disclosure of information related to transactions entered into with related parties. Schedule of Related Party Transactions Activity [Table Text Block] Schedule of activity associated with related party transactions Tabular disclosure of activity associated with related party transactions. Integrys Energy Services [Member] Integrys Energy Services Represents activity related to Integrys Energy Services, Inc.. Wisconsin Public Service Leasing [Member] WPS Leasing Represents activity related to WPS Leasing. Defined Benefit Unfunded Non Qualified Plan Pension Obligation Transferred to Related Parties Pension obligation transferred to related parties Represents pension obligation transferred to related parties. Period Within Which Notice is due if Operation Permit is Required to be Submitted Period within which notice is due if operation permit is required to be submitted Represents period within which notice is due if operation permit is required to be submitted. Income from Equity Portion of AFUDC [Member] Equity portion of AFUDC Represents information pertaining to the income from equity portion of AFUDC. Fox Energy Company LLC [Member] Fox Energy Company, LLC Represents information pertaining to Fox Energy Company, LLC, owner of a combined-cycle electric generating facility. Contract Termination Costs Payment to be made for terminating tolling arrangement Represents the amount of costs which will be incurred to terminate an existing contract. Contract termination fee related to tolling arrangement Common Equity Ratio to be Maintained Represents the common equity ratio which is required to be maintained. Common equity ratio required to be maintained (as a percent) Share Based Compensation Arrangement by Share Based Payment Award Equity Instruments other than Options Award Modifications Weighted Average Grant Date Fair Value Award modifications (in dollars per share) Weighted-average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were modified during the period as per the agreement made under the plan. AGREEMENT TO PURCHASE FOX ENERGY CENTER Pending Purchase Disclosure [Text Block] AGREEMENT TO PURCHASE FOX ENERGY CENTER Disclosure relating to a pending acquisition. Capacity of Fox Energy Center (in megawatts) Represents the capacity of an electric generating facility. Capacity of Electric Generating Facility Year of Rate Cases [Domain] Year for which the rate cases are filed. Rates 2013 [Member] 2013 Rates Rate case application filed for year 2013. Rates 2012 [Member] 2012 Rates Rate case application filed for year 2012. Accrual for Environmental Loss Contingencies Estimated and accrued future undiscounted investigation and cleanup costs for all sites Rates 2011 [Member] 2011 Rates Rate case application filed for year 2011. Cash Flow Reclassification [Member] Cash flow reclassification Represents activity related to reclassification of cash flow activity between operating, investing or financing activities. Regulatory Authorities Approved and Updated Settlement Agreement [Member] Settlement agreement Represents information pertaining to the approved and updated settlement agreement by regulatory authorities. Authorized Rate Annual Cap under Decoupling Mechanism Annual cap on rates Represents the annual cap on authorized rates under decoupling mechanism which will be based on total rate case-approved margins, rather than being calculated on a per-customer basis. Authorized recovery of income tax amounts previously expensed related to the Federal Health Care Reform Act Represents the income tax amount previously expensed by the entity that was authorized to be recovered. Authorized Recovery of Income Tax Expense Accrued Environmental Loss Contingencies, Noncurrent Environmental remediation liabilities Accumulated Other Comprehensive Income (Loss) [Member] Accumulated Other Comprehensive Income (Loss) Accumulated Deferred Investment Tax Credit Deferred investment tax credits Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Property, plant, and equipment, accumulated depreciation (in dollars) Additional Paid in Capital, Common Stock Additional paid-in capital Additional Paid-in Capital [Member] Additional Paid in Capital Adjustments to reconcile net income to net cash provided by operating activities Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] All Other Segments [Member] Other Allocated Share-based Compensation Expense Total stock-based compensation expense Allowance for Doubtful Accounts Receivable, Current Accounts receivable and accrued unbilled revenues, reserves (in dollars) Amount of Restricted Net Assets for Consolidated and Unconsolidated Subsidiaries Total restricted net assets ASSET RETIREMENT OBLIGATIONS Asset Retirement Obligation Disclosure [Text Block] ASSET RETIREMENT OBLIGATIONS Assets, Fair Value Disclosure Fair Value, Assets Assets Assets [Abstract] Assets, Current Current assets Assets Total assets Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Pending purchase Business Acquisition [Line Items] Payment to be made for the acquisition of Fox Energy Company LLC Business Acquisition, Cost of Acquired Entity, Purchase Price Capital Expenditures Incurred but Not yet Paid Construction costs funded through accounts payable Capitalization, Long-term Debt and Equity Total capitalization Carrying (Reported) Amount, Fair Value Disclosure [Member] Carrying Amount Cash and cash equivalents at end of period Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents Cash and cash equivalents at beginning of period CASH AND CASH EQUIVALENTS Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Significant noncash transactions Class of Stock [Domain] Coal Contract [Member] Coal contract Commercial Paper [Member] Commercial paper Commitments and Contingencies Disclosure [Text Block] COMMITMENTS AND CONTINGENCIES COMMITMENTS AND CONTINGENCIES Commitments and Contingencies. Commitments and contingencies Common Stock [Member] Common Stock Common Stock, Shares, Outstanding Common stock, shares outstanding Common Stock, Value, Issued Common stock - $4 par value; 32,000,000 shares authorized; 23,896,962 shares issued and outstanding Common stock - $4 par value; 32,000,000 shares authorized; 23,896,962 shares outstanding Common Stock, Shares, Issued Common stock, shares issued Common Stock, Par or Stated Value Per Share Common stock, par value (in dollars per share) Common Stock, Shares Authorized Common stock, shares authorized EMPLOYEE BENEFIT PLANS Comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Comprehensive Income [Member] Comprehensive Income Cost of Purchased Power Purchased power Customer Advances, Current Customer credit balances Current portion of long-term debt Long-term Debt, Gross Debt Instrument [Line Items] LONG-TERM DEBT Schedule of Long-term Debt Instruments [Table] LONG-TERM DEBT Debt Instrument [Axis] Debt Instrument, Face Amount Face amount Debt Instrument, Name [Domain] Debt Instrument, Unamortized Discount Unamortized discount on long-term debt Debt Instrument, Interest Rate, Stated Percentage Interest rate, (as a percent) Stated interest rate (as a percent) Deferred Tax Liabilities, Gross, Noncurrent Deferred income taxes Deferred Costs, Current Deferred costs related to CSAPR Deferred Income Taxes and Tax Credits Deferred income taxes and investment tax credits Deferred Tax Assets, Net of Valuation Allowance, Current Deferred income taxes Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Amortization of prior service cost (credit) Defined Benefit Plan, Estimated Future Employer Contributions in Current Fiscal Year Additional contributions to plans during the remainder of fiscal year Defined Benefit Plan, Contributions by Employer Contribution to the plans Defined Benefit Plan, Amortization of Gains (Losses) Amortization of net actuarial loss Defined Benefit Plan Disclosure [Line Items] Components of net periodic benefit cost Defined Benefit Plan, Amortization of Transition Obligations (Assets) Amortization of transition obligation Defined Benefit Plan, Expected Return on Plan Assets Expected return on plan assets Defined Benefit Plans and Other Postretirement Benefit Plans [Axis] Defined Benefit Plan, Interest Cost Interest cost Defined Benefit Plan, Net Periodic Benefit Cost Net periodic benefit cost Defined Benefit Plan, Service Cost Service cost Defined Benefit Plans and Other Postretirement Benefit Plans [Domain] Defined Benefit Plan, Net Periodic Benefit Cost [Abstract] Components of net periodic benefit cost Depreciation, Depletion and Amortization Depreciation and amortization expense Derivative Instrument Risk [Axis] Derivative Instruments and Hedges, Noncurrent Other long-term assets from risk management activities Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net Unrealized gains (losses) Derivative Instruments and Hedges, Assets Assets from risk management activities Other current assets from risk management activities Derivative [Line Items] Risk management activities Derivative Instruments and Hedging Activities Disclosure [Text Block] RISK MANAGEMENT ACTIVITIES Derivative, Collateral, Right to Reclaim Cash Cash collateral provided to others Derivative [Table] RISK MANAGEMENT ACTIVITIES Derivative Asset, Fair Value, Gross Asset Risk management assets Derivative Liability, Fair Value, Gross Liability Risk management liabilities Derivative Contract Type [Domain] Derivatives, Fair Value [Line Items] Derivative assets and liabilities from risk management activities Description of New Accounting Pronouncements Not yet Adopted [Text Block] NEW ACCOUNTING PRONOUNCEMENTS Direct Operating Costs Cost of fuel, natural gas, and purchased power Disclosure of Compensation Related Costs, Share-based Payments [Text Block] STOCK-BASED COMPENSATION STOCK-BASED COMPENSATION Dividends, Preferred Stock, Cash Preferred stock dividend requirements Dividends, Common Stock, Cash Dividends to parent Due from Related Parties, Current Receivables from related parties Due from Related Parties, Noncurrent Receivables from related parties Liability related to income tax allocation Due to Related Parties Due to Related Parties, Current Payables to related parties Due to Related Parties, Noncurrent Payables to related parties Effective Income Tax Rate, Continuing Operations Effective Tax Rate (as a percent) Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate Federal statutory tax rate (as a percent) Electric Production Expense Electric production fuels Electric Domestic Regulated Revenue Electric Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition Weighted-average period over which compensation cost is to be recognized Employee Service Share-based Compensation, Tax Benefit from Compensation Expense Deferred Income tax benefit Employee Service Share-based Compensation, Cash Received from Exercise of Stock Options Cash received from option exercises (in dollars) Compensation cost not yet recognized Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Stock Options Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Share-based Awards Other than Options Compensation cost related to unvested and outstanding awards not yet recognized Environmental Remediation Obligations [Abstract] Environmental remediation obligations Ownership interest (as a percent) Equity Method Investment, Ownership Percentage. Equity Component [Domain] Equity Method Investee, Name [Domain] Estimate of Fair Value, Fair Value Disclosure [Member] Total Fair Value Measurement Frequency [Axis] Fair Value, Hierarchy [Axis] Fair Value, Measurements, Recurring [Member] Fair value measurements on a recurring basis Fair Value, Measurement Frequency [Domain] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair value of assets and liabilities on a recurring basis FAIR VALUE Fair Value Disclosures [Text Block] FAIR VALUE Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Carrying value and estimated fair value of financial instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Schedule of carrying value and estimated fair value of financial instruments Fair Value, Disclosure Item Amounts [Domain] Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping, Disclosure Item Amounts [Axis] Fair Value, Inputs, Level 3 [Member] Level 3 Fair Value, Inputs, Level 1 [Member] Level 1 Fair Value, Inputs, Level 2 [Member] Level 2 Gas Domestic Regulated Revenue Natural gas Goodwill Goodwill GUARANTEES GUARANTEES Guarantees [Text Block] Hedging Designation [Axis] Hedging Designation [Domain] Intersegment Elimination [Member] Reconciling Eliminations Income before taxes Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest Income (Loss) from Equity Method Investments [Member] Earnings in equity-method investments Income (Loss) from Equity Method Investments, Net of Dividends or Distributions Equity income, net of dividends CONDENSED CONSOLIDATED STATEMENTS OF INCOME Income Tax Disclosure [Text Block] INCOME TAXES INCOME TAXES Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest Income before taxes Income from equity method investee Income (Loss) from Equity Method Investments Income Tax Expense (Benefit) Provision for income taxes Provision (benefit) for income taxes Income Taxes Paid, Net Cash (received) paid for income taxes Accrued Taxes Increase (Decrease) in Accrued Taxes Payable Increase (Decrease) in Allowance for Equity Funds Used During Construction Allowance for equity funds used during construction Increase (Decrease) in Accounts Payable Accounts payable Increase (Decrease) in Prepaid Taxes Prepaid taxes Decrease in the provision for income taxes resulting from the entity's 2013 rate case settlement agreement Increase (Decrease) in Income Taxes Increase (Decrease) in Margin Deposits Outstanding Collateral on deposit Changes in working capital Increase (Decrease) in Operating Capital [Abstract] Increase (Decrease) in Other Operating Assets Other current assets Change in other current assets Increase (Decrease) in Inventories Inventories Change in inventories Increase (Decrease) in Other Operating Liabilities Other current liabilities Increase (Decrease) in Receivables Accounts receivable and accrued unbilled revenues Increase (Decrease) in Shareholder's Equity Increase (Decrease) in Stockholders' Equity [Roll Forward] Interest Expense Interest expense Interest expense Interest expense Interest Expense, Related Party Interest Paid Cash paid for interest Inventory, Net [Abstract] Inventories Inventory, Net Inventories Fuel and gas Inventory, Raw Materials, Gross Letters of Credit Outstanding, Amount Letters of credit issued inside credit facilities Long-term Debt, Type [Domain] Long-term Debt, Type [Axis] LEASES Leases of Lessee Disclosure [Text Block] LEASES Liabilities, Current Current liabilities Liabilities, Fair Value Disclosure Fair Value, Liabilities Liabilities [Abstract] Liabilities Liabilities, Noncurrent Long-term liabilities Liabilities and Shareholders' Equity Liabilities and Equity [Abstract] Liabilities and Equity Total liabilities and shareholders' equity Line of Credit Facility, Maximum Borrowing Capacity Total short-term credit capacity Line of Credit Facility, Remaining Borrowing Capacity Available capacity under existing agreements Total Long-term Debt. Long-term Debt, Fair Value Long-term debt Long-term Debt [Text Block] LONG-TERM DEBT Current portion of long-term debt Current portion of long-term debt Long-term Debt, Current Maturities Long-term Debt, Excluding Current Maturities Long-term debt Total long-term debt Loss Contingencies [Table] Loss Contingency, Information about Litigation Matters [Abstract] Environmental Loss Contingency Nature [Axis] Loss Contingencies [Line Items] Environmental Loss Contingency, Nature [Domain] Loss Contingency, Range of Possible Loss, Maximum Fines, penalties, and costs of supplemental environmental projects associated with settlements, high end of range Loss Contingency, Range of Possible Loss, Minimum Fines, penalties, and costs of supplemental environmental projects associated with settlements, low end of range Margin Deposit Assets Collateral on deposit Market Approach Valuation Technique [Member] Valuation Technique: Market-based Maturities of Senior Debt Redemption of long-term debt Maximum [Member] Maximum Minimum [Member] Minimum Nature of Error [Domain] Financing Activities Net Cash Provided by (Used in) Financing Activities, Continuing Operations [Abstract] Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities, Continuing Operations Operating Activities Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract] Net Cash Provided by (Used in) Continuing Operations Net change in cash and cash equivalents Net cash used for investing activities Net Cash Provided by (Used in) Investing Activities, Continuing Operations Net Income (Loss) Available to Common Stockholders, Basic Net income attributed to common shareholder Net income (loss) attributed to common shareholder Net cash used for financing activities Net Cash Provided by (Used in) Financing Activities, Continuing Operations Investing Activities Net Cash Provided by (Used in) Investing Activities, Continuing Operations [Abstract] Net Income (Loss) Attributable to Parent Net income Net income New Contract [Axis] New Contract [Domain] NEW ACCOUNTING PRONOUNCEMENTS Nonmonetary Notional Amount of Price Risk Derivative Instruments Not Designated as Hedging Instruments Notional volume of outstanding derivative contracts Nonoperating Income (Expense) Other expense Notes Payable, Related Parties, Noncurrent Long-term debt to parent Total long-term debt to parent Notes payable Notes Payable to Banks [Member] Short-term notes payable Number of Reportable Segments Number of reportable segments Not Designated as Hedging Instrument [Member] Non-hedge derivatives Operating Expense [Member] Income Statement - Operating and maintenance expense Operating Income (Loss) Operating income FINANCIAL INFORMATION Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] FINANCIAL INFORMATION Other Assets, Current Other current assets MISCELLANEOUS INCOME Other Other Operating Activities, Cash Flow Statement Other Assets, Noncurrent Other long-term assets Other Cost and Expense, Operating Operating and maintenance expense Other Income and Other Expense Disclosure [Text Block] MISCELLANEOUS INCOME Other Liabilities, Current Other current liabilities Other Nonoperating Income (Expense) Miscellaneous income Total miscellaneous income Other Liabilities, Noncurrent Other long-term liabilities Other Inventory, Supplies, Gross Materials and supplies, at average cost Other Postretirement Benefit Plans, Defined Benefit [Member] Other Postretirement Benefits Parent Company [Member] Integrys Energy Group Payments for (Proceeds from) Other Investing Activities Other Payments of Distributions to Affiliates Dividends to parent Common stock dividends paid Capital returned Payments of Capital Distribution Return of capital to parent Payments to Acquire Property, Plant, and Equipment Capital expenditures Payments of Ordinary Dividends, Preferred Stock and Preference Stock Preferred stock dividend requirements Payments of Ordinary Dividends, Common Stock Dividends to parent Pension Plans, Defined Benefit [Member] Pension Benefits Pension and Other Postretirement Benefits Disclosure [Text Block] EMPLOYEE BENEFIT PLANS Pension and Other Postretirement Benefit Contributions Pension and other postretirement contributions Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent Pension and other postretirement benefit obligations Pension and Other Postretirement Benefit Expense Pension and other postretirement expense Performance Shares [Member] Performance stock rights Performance Stock Rights Preferred Stock, Value, Issued Preferred stock - $100 par value; 1,000,000 shares authorized; 511,882 shares issued and outstanding Total preferred stock Preferred stock Preferred Stock, Shares Authorized Preferred stock, shares authorized Preferred Stock, Dividend Rate, Percentage Preferred stock, Dividend Rate, (as a percent) PREFERRED STOCK Preferred Stock [Text Block] Preferred Stock, Shares Issued Preferred stock, shares issued Preferred Stock, Par or Stated Value Per Share Preferred stock, par value (in dollars per share) Preferred Stock, Shares Outstanding Preferred stock, shares outstanding Cumulative; $100 par value; 1,000,000 shares authorized with no mandatory redemption - Shares Outstanding Prepaid Taxes Prepaid taxes Proceeds from Contributions from Affiliates Receipt of capital contribution Other Proceeds from (Payments for) Other Financing Activities Other Proceeds from Contributions from Parent Equity contribution from parent Proceeds from (Repayments of) Short-term Debt, Maturing in Three Months or Less Short-term debt, net Proceeds from Decommissioning Trust Fund Assets Refund of nonqualified decommissioning fund Proceeds from Issuance of Long-term Debt Issuance of long-term debt Proceeds from Sale of Property, Plant, and Equipment Proceeds from the sale or disposal of assets PROPERTY, PLANT, AND EQUIPMENT Property, Plant and Equipment, Net Property, plant, and equipment, net of accumulated depreciation of $1,335.6 and $1,280.7, respectively Property, Plant and Equipment Disclosure [Text Block] PROPERTY, PLANT, AND EQUIPMENT Provision for Doubtful Accounts Bad debt expense Regulation Status [Axis] Public Utilities Disclosure [Text Block] REGULATORY ENVIRONMENT Reclassification Quantifying Misstatement in Current Year Financial Statements [Line Items] Nature of Error [Axis] Quarterly Financial Information [Text Block] QUARTERLY FINANCIAL INFORMATION (Unaudited) QUARTERLY FINANCIAL INFORMATION (Unaudited) Range [Axis] Range [Domain] Receivables, Net, Current Accounts receivable and accrued unbilled revenues, net of reserves of $4.0 and $3.0, respectively Regulated and Unregulated Operation [Domain] REGULATORY ENVIRONMENT Regulated Operation [Member] Regulated Utilities Regulatory Liability, Noncurrent Regulatory liabilities Regulatory Assets, Current Regulatory assets Regulatory Liability, Current Regulatory liabilities Regulatory Assets, Noncurrent Regulatory assets REGULATORY ASSETS AND LIABILITIES Related Party Transaction, Purchases from Related Party Purchases from related party Purchases of energy from equity method investee Related Party Transactions Disclosure [Text Block] RELATED PARTY TRANSACTIONS RELATED PARTY TRANSACTIONS Related Party Transaction [Line Items] Charges to equity method investee for services and construction Related Party Transaction, Other Revenues from Transactions with Related Party Related Party [Domain] Charges from equity method investee for network transmission services Related Party Transaction, Expenses from Transactions with Related Party RELATED PARTY TRANSACTIONS Related Party [Axis] Repayments of Related Party Debt Repayment of long-term debt to parent Repayments of Long-term Debt Repayment of long-term debt Repayments of Notes Payable Repayment of notes payable Adjustment Restatement Adjustment [Member] Restricted Stock Units (RSUs) [Member] Restricted Share Units RESTRUCTURING EXPENSE Restructuring and Related Activities Disclosure [Text Block] Restructuring Charges Restructuring expense RESTRUCTURING EXPENSE Retained Earnings (Accumulated Deficit) Retained earnings Retained Earnings [Member] Retained Earnings Retained Earnings, Undistributed Earnings from Equity Method Investees Equity in undistributed earnings of 50% or less owned investees accounted under equity method investments Sales to related party Revenues from services provided to equity method investee Revenue from Related Parties Segment Reporting Information, Intersegment Revenue Intersegment revenues Revenues Operating revenues External revenues Operating revenues Revenues [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Exercisable at the end of the period Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Expected term Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Exercisable at the end of the period Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Outstanding at the end of the period Short-term Debt, Average Outstanding Amount Average amount of short-term borrowings outstanding Scenario, Unspecified [Domain] Schedule of assets and liabilities that were accounted for at fair value on a recurring basis, categorized by level within the fair value hierarchy Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] REGULATORY ASSETS AND LIABILITIES Schedule of Regulatory Assets and Liabilities [Text Block] Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block] Summary of stock option activity and information related to outstanding and exercisable stock options Schedule of Net Benefit Costs [Table Text Block] Schedule of components of net periodic benefit cost for benefit plans Schedule of Nonvested Performance-based Units Activity [Table Text Block] Summary of the activity related to performance stock rights Schedule of Share-based Compensation, Restricted Stock Units Award Activity [Table Text Block] Summary of activity related to all restricted share unit awards (equity and liability awards) Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Schedule of supplemental disclosure to statements of cash flows Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Schedule of weighted-average fair values per stock option along with the assumptions incorporated into the valuation model Schedule of Capitalization Schedule of Capitalization [Line Items] Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block] Schedule of stock-based compensation expense and the related deferred tax benefit recognized in income Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Defined Benefit Plans Disclosures [Table] Equity Method Investee, Name [Axis] Schedule of Line of Credit Facilities [Table Text Block]