Organization, Consolidation and Presentation of Financial Statements [Abstract] Increase in income tax expense resulting from purchase accounting adjustment Income Tax Expense (Benefit), Purchase Accounting Adjustment Income Tax Expense (Benefit), Purchase Accounting Adjustment Decrease in goodwill resulting from purchase accounting adjustment Goodwill, Purchase Accounting Adjustments Variable Interest Entities [Abstract] Variable Interest Entities Abstract. Schedule of Variable Interest Entities [Table] Schedule of Variable Interest Entities [Table] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] FES FES [Member] Fes. OE OE [Member] Oe. Other First Energy Subsidiaries Other First Energy Subsidiaries [Member] Other FirstEnergy subsidiaries. Variable Interest Entity [Line Items] Variable Interest Entity [Line Items] Net exposure to loss based upon the casualty value provisions Net exposure to loss based upon casualty value provisions [Abstract] Net exposure to loss based upon casualty value provisions. Maximum Exposure Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount Discounted Lease Payments, net Variable interest entities discounted lease payments net Discounted Lease Payments, net. Variable Interest Entities Net Exposure Variable Interest Entities Net Exposure Variable Interest Entities Net Exposure. Derivative Instruments and Hedging Activities Disclosure [Abstract] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Derivative Instrument Risk [Axis] Derivative Instrument Risk [Axis] Derivative Contract Type [Domain] Derivative Contract Type [Domain] Power Contracts Power Contracts [Member] Power contracts. FTRs Ftrs [Member] Fire steel resources. NUGs Nugs [Member] NUGs. Other Other [Member] Derivatives Fair Value By Balance Sheet Location [Axis] Derivatives, Fair Value, by Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Current Assets Current Assets [Member] Current assets. Current Liabilities Current Liabilities [Member] Current liabilities. Noncurrent Assets Noncurrent Assets [Member] Noncurrent assets. Noncurrent Liabilities Noncurrent Liabilities [Member] Noncurrent liabilities. Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Fair value of commodity derivatives Derivative, Fair Value, Net [Abstract] Economic Hedges Derivative assets Derivative Asset, Fair Value, Gross Asset Economic Hedges Derivative liabilities Derivative Liability, Fair Value, Gross Liability Commitments and Contingencies Disclosure [Abstract] Schedule of Guarantor Obligations [Table] Schedule of Guarantor Obligations [Table] AE Supply Ae Supply [Member] AE Supply. Utilities Utilities [Member] Utilities. Payment and Performance Risk (Credit Rating) [Axis] Payment and Performance Risk (Credit Rating) [Axis] Credit Rating [Domain] Credit Rating [Domain] Credit Rating Downgrade to Below Investment Grade Credit Rating Downgrade to Below Investment Grade [Member] Credit Rating Downgrade to Below Investment Grade [Member] Material Adverse Event Material Adverse Event [Member] Material Adverse Event. Guarantor Obligations [Line Items] Guarantor Obligations [Line Items] Maximum exposure under collateral provisions Guarantor Obligations, Maximum Exposure, Undiscounted Potential Acceleration Payments or Funding Obligations Due to Credit Rating Downgrade Potential Acceleration Payments or Funding Obligations Due to Credit Rating Downgrade Potential Acceleration Payments or Funding Obligations Due to Credit Rating Downgrade Potential Acceleration Payments or Funding Obligations Due to a Material Adverse Event Potential Acceleration Payments or Funding Obligations Due to a Material Adverse Event Potential Acceleration Payments or Funding Obligations Due to a Material Adverse Event Supplemental Guarantor Information [Abstract] Supplemental Guarantor Information Abstract. SUPPLEMENTAL GUARANTOR INFORMATION Supplemental Guarantor Information Disclosure [Text Block] Supplemental Guarantor Information Disclosure Text Block. Fair Value Disclosures [Abstract] Fair Value Inputs, Assets and Liabilities, Quantitative Information [Table] Fair Value Inputs, Assets and Liabilities, Quantitative Information [Table] Fair Value Inputs, Assets and Liabilities, Quantitative Information [Table] Valuation Technique [Axis] Valuation Technique [Axis] Information by valuation technique. Valuation Technique [Domain] Valuation Technique [Domain] Valuation techniques used by the entity. Model Model [Member] Model [Member] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value, Measurements, Fair Value Hierarchy [Domain] Level 3 Fair Value, Inputs, Level 3 [Member] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Weighted Average [Member] Weighted Average [Member] Weighted Average [Member] Non Utility Generation contract Non Utility Generation Contract [Member] NUG Contract Member. JCP&L Jcp And L [Member] JCP&L. Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] Fair Value Fair Value Measurements With Unobservable Inputs Reconciliation Recurring Basis Asset And Liability Net Value Fair value measurements with unobservable inputs reconciliation recurring basis asset and liability net value. Fair Value Inputs, RTO Auction Clearing Prices Fair Value Inputs, RTO Auction Clearing Prices Fair Value Inputs, RTO Auction Clearing Prices Fair Value Inputs, Generation Fair Value Inputs, Generation Fair Value Inputs, Generation Fair Value Inputs, Power, Regional Prices Fair Value Inputs, Power, Regional Prices Fair Value Inputs, Power, Regional Prices Schedule of Guarantor Obligations Schedule of Guarantor Obligations [Table Text Block] Earnings Per Share [Abstract] EARNINGS PER SHARE Earnings Per Share [Text Block] Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Fair Value by Balance Sheet Grouping Disclosure Item Amounts [Axis] Fair Value, by Balance Sheet Grouping, Disclosure Item Amounts [Axis] Fair Value Disclosure Item Amounts [Domain] Fair Value, Disclosure Item Amounts [Domain] Carrying Value Carrying (Reported) Amount, Fair Value Disclosure [Member] Fair Value Estimate of Fair Value, Fair Value Disclosure [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair value and related carrying amounts of long-term debt and other long-term obligations Fair value and related carrying amounts of long term debt and other long term obligations [Abstract] Fair value and related carrying amounts of long-term debt and other long-term obligations. Long-term debt and other long-term obligations Long-term Debt and Capital Lease Obligations Supplemental Guarantor Information (Textuals) [Abstract] Supplemental Guarantor Information (Textuals) [Abstract] Supplemental Guarantor Information. Sale and leaseback transactions of undivided interest Bruce Mansfield Sale And Leaseback Transactions Of Undivided Interest Sale and leaseback transactions of undivided interest. Schedule of Condensed Financial Statements [Table] Schedule of Condensed Financial Statements [Table] FES Corp FES Corp [Member] -- None. No documentation exists for this element. -- FGCO Non-Guarantor Subsidiaries [Member] Nuclear Generation Corp Nuclear Generation Corp [Member] Nuclear Generation Corp. Eliminations Consolidation, Eliminations [Member] Condensed Financial Statements, Captions [Line Items] Condensed Financial Statements, Captions [Line Items] Consolidated Statements of Cash Flows [Abstract] Statement of Cash Flows [Abstract] NET CASH PROVIDED FROM (USED FOR) OPERATING ACTIVITIES Net Cash Provided by (Used in) Operating Activities CASH FLOWS FROM FINANCING ACTIVITIES: Net Cash Provided by (Used in) Financing Activities [Abstract] New Financing- New Financing [Abstract] New Financing Abstract. Long-term debt Proceeds from Issuance of Long-term Debt Short-term borrowings, net Proceeds from Short-term Debt Redemptions and Repayments- Redemptions And Repayments [Abstract] Redemptions And Repayments Abstract. Long-term debt Repayments of Long-term Debt Short-term borrowings, net Repayments of Short-term Debt Other Proceeds from (Payments for) Other Financing Activities Net cash provided from (used for) financing activities Net Cash Provided by (Used in) Financing Activities CASH FLOWS FROM INVESTING ACTIVITIES: Net Cash Provided by (Used in) Investing Activities [Abstract] Property additions Payments to Acquire Productive Assets Sales of investment securities held in trusts Proceeds from Sale of Available-for-sale Securities Purchases of investment securities held in trusts Payments to Acquire Available-for-sale Securities Loans to affiliated companies, net Proceeds from Collection of (Payments to Fund) Long-term Loans to Related Parties Customer acquisition costs Payments to Acquire Intangible Assets Other Payments for (Proceeds from) Other Investing Activities Net cash provided from (used for) investing activities Net Cash Provided by (Used in) Investing Activities Net change in cash and cash equivalents Cash and Cash Equivalents, Period Increase (Decrease) Cash and cash equivalents at beginning of period Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents at end of period Related Party Transactions, by Related Party [Axis] Related Party [Domain] Affiliates [Member] Affiliates. Consolidating Balance Sheets Statement of Financial Position [Abstract] ASSETS Assets [Abstract] CURRENT ASSETS: Assets, Current [Abstract] Cash and cash equivalents Receivables- Receivables, Net, Current [Abstract] Customers Accounts Receivable, Net, Current Affiliated companies Accounts Receivable, Related Parties, Current Other Other Receivables Notes receivable from affiliated companies Notes Receivable, Related Parties, Current Materials and supplies, at average cost Inventory, Net Derivatives Derivative Assets, Current Prepayments and other Other Assets, Current Total current assets Assets, Current PROPERTY, PLANT AND EQUIPMENT: Property, Plant and Equipment, Net [Abstract] In service Property, Plant and Equipment, Gross Less - Accumulated provision for depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Property, plant and equipment in service net of accumulated provision for depreciation Net Plant Excluding Construction Work In Progress Net Plant Excluding Construction Work In Progress. Construction work in progress Construction in Progress, Gross Total net property, plant and equipment Property, Plant and Equipment, Net INVESTMENTS: Investments [Abstract] Nuclear plant decommissioning trusts Decommissioning Fund Investments Investment in affiliated companies Investment in associated companies Investment in associated companies. Other Other Long-term Investments Total other property and investments Long-term Investments DEFERRED CHARGES AND OTHER ASSETS: Deferred Charges And Other Assets [Abstract] Deferred Charges And Other Assets Abstract. Accumulated deferred income tax benefits Deferred Tax Assets, Deferred Income Customer intangibles Finite-Lived Intangible Assets, Net Goodwill Goodwill Property taxes Property taxes Property taxes. Unamortized sale and leaseback costs Unamortized sale and leaseback costs Unamortized sale and leaseback costs. Derivatives Derivative Assets, Noncurrent Other Other Assets, Noncurrent Total deferred charges and other assets Assets, Noncurrent Total assets Assets LIABILITIES AND CAPITALIZATION Liabilities And Capitalization [Abstract] Liabilities And Capitalization Abstract. CURRENT LIABILITIES: Liabilities, Current [Abstract] Currently payable long-term debt Long-term Debt and Capital Lease Obligations, Current Short-term borrowings- Short-term Debt [Abstract] Affiliated companies Short-term Debt Accounts payable- Accounts Payable and Accrued Liabilities, Current [Abstract] Affiliated companies Accounts Payable, Related Parties, Current Other Accounts Payable, Other, Current Accrued Taxes Accrued Income Taxes, Current Derivatives Derivative Liabilities, Current Other Other Liabilities, Current Total current liabilities Liabilities, Current CAPITALIZATION: Capitalization, Long-term Debt and Equity [Abstract] Total equity Stockholders' Equity Attributable to Parent Total capitalization Capitalization, Long-term Debt and Equity NONCURRENT LIABILITIES: Liabilities, Noncurrent [Abstract] Deferred gain on sale and leaseback transaction Sale Leaseback Transaction, Deferred Gain, Net Accumulated deferred income taxes Deferred Tax Liabilities, Noncurrent Asset retirement obligations Asset Retirement Obligations, Noncurrent Retirement benefits Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent Lease market valuation liability Off-market Lease, Unfavorable Other Other Liabilities, Noncurrent Total noncurrent liabilities Liabilities, Noncurrent Total liabilities and capitalization Liabilities and Equity Reconciliation of basic and diluted earnings per share Schedule of Earnings Per Share Reconciliation [Table Text Block] Significant Accounting Policies [Abstract] Significant Accounting Policies [Abstract] Earnings Per Share, Policy [Policy Text Block] Earnings Per Share, Policy [Policy Text Block] Pension and Other Postretirement Plans, Policy [Policy Text Block] Pension and Other Postretirement Plans, Policy [Policy Text Block] Consolidation, Variable Interest Entity, Policy [Policy Text Block] Consolidation, Variable Interest Entity, Policy [Policy Text Block] Income Tax Disclosure [Abstract] INCOME TAXES Income Tax Disclosure [Text Block] Derivative [Table] Derivative [Table] Derivative By Nature [Axis] Derivative, by Nature [Axis] Derivative Name [Domain] Derivative, Name [Domain] Natural Gas Futures Natural Gas Futures [Member] Natural Gas Futures [Member] Derivative [Line Items] Derivative [Line Items] Volume of First Energy's outstanding derivative transactions Volume Of Parent Companys Outstanding Derivative Transaction [Abstract] Volume of parent companys outstanding derivative transaction. Purchases Volume Of Derivatives, Purchases Volume Of Derivatives, Purchases Sales Volume Of Derivatives, Sales Volume Of Derivatives, Sales Net Volume Of Derivatives, Net Volume Of Derivatives, Net Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Line Items] Schedule of Available-for-sale Securities [Line Items] Proceeds from the sale of investments in available-for-sale securities, realized gains and losses on those sales, and interest and dividend income Available-for-sale Securities, Gross Realized Gain (Loss), Disclosures [Abstract] Sales Proceeds Available-for-sale Securities, Gross Realized Gains (Losses), Sale Proceeds Realized gains Available-for-sale Securities, Gross Realized Gains Realized losses Available-for-sale Securities, Gross Realized Losses Interest and dividend income Investment Income From Trusts Investment Income From Trusts Regulatory Accounting [Axis] Regulatory Accounting [Axis] Regulatory Accounting [Axis] Regulatory Accounting [Domain] Regulatory Accounting [Domain] Regulatory Accounting [Domain] Subject to Regulatory Accounting, Excluded from Earnings Subject to Regulatory Accounting, Excluded from Earnings [Member] Subject to Regulatory Accounting, Excluded from Earnings [Member] Cash Flow Hedges Cash Flow Hedges [Member] Cash Flow Hedges Member. Fair Value Hedging Fair Value Hedging [Member] Unrealized Gain (Loss) on Derivatives Unrealized Gain (Loss) on Derivatives Unamortized gains or losses associated with designated cash flow hedges Unamortized Gains Or Losses Associated With Designated Cash Flow Hedges Unamortized gains or losses associated with designated cash flow hedges. Reclassifications from AOCL into other operating expense Reclassifications From Accumulated Other Comprehensive Loss Into Other Operating Expense Reclassifications from AOCL into other operating expense. Losses to be amortized to interest expenses during next twelve months Losses To Be Amortized To Interest Expenses During Next Twelve Months Losses To Be Amortized To Interest Expenses During Next Twelve Months. Number of Interest Rate Swap Agreements Number Of Interest Rate Swap Agreements Number of Interest Rate Swap Agreements. Unamortized gains or losses associated with prior interest rate hedges Unamortized losses associated with prior interest rate hedges Unamortized losses associated with prior interest rate hedges. Reclassifications from accumulated other comprehensive loss Reclassifications from Accumulated Other Comprehensive Loss Reclassifications from accumulated other comprehensive loss. Gains included in long-term debt associated with prior fixed-for-floating interest rate swap agreements Unamortized gains included in long term debt associated with prior fixed for floating interest rate swap agreements Unamortized gains included in long-term debt associated with prior fixed-for-floating interest rate swap agreements. Reclassifications from long-term debt Reclassifications From Long Term Debt Reclassifications from long-term debt. Net asset position under commodity derivative contracts Derivative Asset, Fair Value, Net Collateral posted Collateral Already Posted, Aggregate Fair Value Additional collateral related to commodity derivatives Additional Collateral, Aggregate Fair Value Expected adverse change in quoted market prices of derivative instruments Expected Adverse Change In Quoted Market Prices Derivative Instruments Expected adverse change in quoted market prices derivative instruments. Decrease net income due to adverse change in commodity prices Decrease Net Income Due To Adverse Change In Commodity Prices Decrease net income due to adverse change in commodity prices. Period In Which LSEs May Request Direct Allocation Of FTRs Period In Which LSEs May Request Direct Allocation Of FTRs Statement [Table] Statement [Table] Statement [Line Items] Statement [Line Items] CASH FLOWS FROM OPERATING ACTIVITIES: Net Cash Provided by (Used in) Operating Activities [Abstract] Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Adjustments to reconcile net income to net cash from operating activities- Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Provision for depreciation Depreciation, Nonproduction Amortization of regulatory assets, net Amortization of Regulatory Asset Deferred costs recoverable as regulatory assets Deferred Costs Recoverable As Regulatory Assets Deferred costs recoverable as regulatory assets. Nuclear fuel and lease amortization Other Amortization of Deferred Charges Deferred purchased power and other costs Deferred Purchased Power Costs Deferred income taxes and investment tax credits, net Deferred Income Taxes and Tax Credits Deferred rents and lease market valuation liability Deferred rents and lease market valuation liability Deferred Rents And Lease Market Valuation Liability. Stock based compensation Share-based Compensation Accrued compensation and retirement benefits Increase (Decrease) in Employee Related Liabilities Purchased power cost recovery reconciliation Purchased power cost recovery reconciliation Purchased power cost recovery reconciliation. Amortization of lease costs Amortization of lease costs Amortization of lease costs. Commodity derivative transactions, net Unrealized Gain (Loss) on Commodity Contracts Accrued regulatory obligations Accrued Regulatory Obligations Accrued regulatory obligations. Pension trust contribution Pension Contributions Asset impairments Asset Impairment Charges Cash collateral, net Increase (Decrease) in Deposits Outstanding Interest rate swap transactions Gain on investment securities held in trusts Gain (Loss) on Sale of Investments Decrease (increase) in operating assets- Increase (Decrease) in Operating Assets [Abstract] Receivables Increase (Decrease) in Accounts and Other Receivables Materials and supplies Increase (Decrease) in Inventories Prepayments and other current assets Increase (Decrease) in Prepaid Expense Prepaid taxes Increase (Decrease) in Prepaid Taxes Increase (decrease) in operating liabilities- Increase (Decrease) in Operating Liabilities [Abstract] Accounts payable Increase (Decrease) in Accounts Payable, Trade Accrued taxes Increase (Decrease) in Income Taxes Payable Accrued interest Increase (Decrease) in Interest Payable, Net Other Increase (Decrease) in Other Operating Assets and Liabilities, Net Net cash provided from (used for) operating activities New financing- Redemptions and Repayments- Common stock Payments for Repurchase of Common Stock Common stock dividend payments Payments of Dividends, Common Stock Equity payment to parent Payments of Capital Distribution Other Proceeds from asset sales Proceeds from Sale of Other Productive Assets Redemptions of lessor notes Redemptions of Lessor Notes Redemptions of lessor notes. Leasehold improvement payments from (to) associated companies Leasehold Improvement Payments From (To) Affiliated Companies Leasehold Improvement Payments From (To) Affiliated Companies Cash investments Payments for (Proceeds from) Investments Cash received in Allegheny merger Cash Acquired from Acquisition Net change in cash and cash equivalents SUPPLEMENTAL CASH FLOW INFORMATION: Supplemental Cash Flow Information [Abstract] Non-cash transaction: merger with Allegheny, common stock issued Stock Issued ORGANIZATION AND BASIS OF PRESENTATION Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Fair Value of Financial Instruments [Table] Fair Value of Financial Instruments [Table] Fair Value Of Financial Instruments. Fair Value of Financial Instruments [Line Items] Fair Value of Financial Instruments [Line Items] Fair Value of Financial Instruments. Assets and liabilities measured on recurring basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Reconciliation of changes in the fair value roll forward of level 3 measurements of NUG contracts Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Quantitative information for level 3 valuation Fair Value, Measurement Inputs, Disclosure [Table Text Block] Amortized cost basis, unrealized gains and losses and fair values of investments in available-for-sale securities Available-for-sale Securities [Table Text Block] Proceeds from the sale of investments in available-for-sale securities, realized gains and losses on those sales, and interest and dividend income Proceeds From Sale Of Investments In Available For Sale Securities Realized Gains And Losses On Those Sales And Interest And Dividend Income [Table Text Block] Proceeds from sale of investments in available-for-sale securities, realized gains and losses on those sales, and interest and dividend income. Amortized cost basis, unrealized gains and losses, and approximate fair values of investments in held-to-maturity securities Held-to-maturity Securities [Table Text Block] Fair value and related carrying amounts of long-term debt and other long-term obligations Fair Value And Related Carrying Amounts Of Long Term Debt And Other Long Term Obligations [Table Text Block] Fair value and related carrying amounts of long-term debt and other long-term obligations. Statement of Income and Comprehensive Income [Abstract] NET INCOME OTHER COMPREHENSIVE INCOME (LOSS): Other Comprehensive Income Loss Abstract OTHER COMPREHENSIVE INCOME:. Pension and OPEB prior service costs Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, before Tax Amortized losses on derivative hedges Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax Change in unrealized gain on available-for-sale securities Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax Other comprehensive loss Other Comprehensive Income (Loss), before Tax Income taxes (benefits) on other comprehensive income (loss) Other Comprehensive Income (Loss), Tax Other comprehensive loss, net of tax Other Comprehensive Income (Loss), Net of Tax COMPREHENSIVE INCOME Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Comprehensive loss attributable to noncontrolling interest Net Income (Loss) Attributable to Noncontrolling Interest COMPREHENSIVE INCOME AVAILABLE TO FIRSTENERGY CORP. Comprehensive Income (Loss), Net of Tax, Attributable to Parent Compensation and Retirement Disclosure [Abstract] Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Defined Benefit Plans Disclosures Defined Benefit Plans [Axis] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Axis] Defined Benefit Plans [Domain] Defined Benefit Plans and Other Postretirement Benefit Plans [Domain] Qualified Pension Plan Pension Plans, Defined Benefit [Member] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Employer Contribution for qualified Plans Defined Benefit Plan, Contributions by Employer Income Statement [Abstract] Excise tax collections included in Revenue Excise Taxes Collected Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Table] Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Table] Fair value assets and liabilities measured on recurring basis unobservable input reconciliation. Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items] Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items] Fair value assets and liabilities measured on recurring basis unobservable input reconciliation. Reconciliation of changes in the fair value of NUG contracts Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract] Beginning Balance, Derivative Asset Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Beginning Balance, Derivative Liability Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value Beginning Balance, Derivative, Total Realized gain (loss), Derivative Asset Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Realized gain loss Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Realized gain loss. Realized gain (loss), Derivative Liability Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Realized gain loss Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Realized gain loss. Realized gain (loss), Derivative Total Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Realized Gain Loss Fair value measurement with unobservable inputs reconciliation recurring basis realized gain loss total. Unrealized gain (loss), Derivative Asset Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset unrealized gain loss Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset unrealized gain loss. Unrealized gain (loss), Derivative Liability Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability unrealized gain loss Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability unrealized gain loss. Unrealized gain (loss), Derivative total Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Unrealized Gain Loss Fair value measurement with unobservable inputs reconciliation recurring basis unrealized gain (loss) total. Purchases, Derivative Asset Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases Purchases, Derivative Liability Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases Purchases, Derivative Asset and Liability, total Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset And Liability Purchases Fair value measurement with unobservable inputs reconciliation recurring basis asset and liability purchases total. Issuances, Derivative Asset Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis,Asset, Issues Issuances, Derivative Liability Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Issues Issuances, Derivative Asset and Liability, total Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset And Liability Issuances Fair value measurement with unobservable inputs reconciliation recurring basis asset and liability issuances total. Sales, Derivative Asset Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales Sales, Derivative Liability Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Sales Sales, Derivative Asset and Liability, total 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 sales total. Settlements, Derivative Asset Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements Settlements, Derivative Liability Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements Settlements, Derivative Asset and Liability, total Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset And Liability Settlements Fair value measurement with unobservable inputs reconciliation recurring basis asset and liability settlements total. Transfers into Level 3, Derivative Asset Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net Transfers into Level 3, Derivative Liability Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Transfers, Net Transfers into Level 3, Derivative Asset and Liability, total Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset And Liability Transfers Net Fair value measurement with unobservable inputs reconciliation recurring basis asset and liability transfers net total. Ending Balance, Derivative Asset Ending Balance, Derivative Liability Ending Balance, Derivative, Total Fair value of derivatives instruments Fair Value Of Commodity Derivatives [Table Text Block] Fair value of commodity derivatives. Volume of First Energy's outstanding derivative transactions Volume Of Parent Companys Outstanding Derivative Transactions [Table Text Block] Volume of parent company's outstanding derivative transactions. Effect of derivative instruments on statements of income and comprehensive income Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance [Table Text Block] Reconciliation of changes in the fair value of certain contracts that are deferred Schedule Of Changes In Fair Value Derivatives Not In Hedging Relationship With Regulatory Offset [Table Text Block] Schedule of changes in fair value derivatives not in hedging relationship with regulatory offset. Pensions OPEB Other Postretirement Benefit Plans, Defined Benefit [Member] Components of Net Periodic Benefit Costs (Credits) Defined Benefit Plan, Net Periodic Benefit Cost [Abstract] Service cost Defined Benefit Plan, Service Cost Interest cost Defined Benefit Plan, Interest Cost Expected return on plan assets Defined Benefit Plan, Expected Return on Plan Assets Amortization of prior service cost Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Other adjustments (settlements, curtailments, etc) Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements and Curtailments Net periodic cost (credit) Defined Benefit Plan, Net Periodic Benefit Cost FAIR VALUE MEASUREMENTS Fair Value Disclosures [Text Block] Schedule of Held-to-maturity Securities [Table] Schedule of Held-to-maturity Securities [Table] Debt Security [Axis] Debt Security [Axis] Major Types of Debt Securities [Domain] Major Types of Debt Securities [Domain] Debt Securities Debt Securities [Member] Schedule Of Held To Maturity Securities [Line Items] Schedule of Held-to-maturity Securities [Line Items] Amortized cost basis, unrealized gains and losses, and approximate fair values of investments in held-to-maturity securities Held-to-maturity Securities, Unclassified [Abstract] Cost Basis Held-to-maturity Securities Unrealized Gains Held-to-maturity Securities, Unrecognized Holding Gain Fair Value Held-to-maturity Securities, Fair Value Segment Reporting [Abstract] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Public Utility Regulated or Unregulated Status [Axis] Public Utility Regulated or Unregulated Status [Axis] Regulated and Unregulated Operation [Domain] Regulated and Unregulated Operation [Domain] Unregulated Plants Expected to be Closed by 9/1/2012 Unregulated Operation [Member] Statement, Business Segments [Axis] Statement, Business Segments [Axis] Segment [Domain] Segment [Domain] Regulated Distribution Regulated Distribution [Member] Regulated Distribution. Competitive Energy Services Competitive Energy Services [Member] Competitive Energy Services. Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Reportable Operating Segments Reportable Operating Segments Reportable Operating Segments. Number of existing utility operating companies Number Of Existing Utility Operating Companies Number of existing utility operating companies. Number of customers served by utility operating companies Number Of Customers Number Of Customers. Number of square miles in service area Service Area Service Area. Megawatts of net demonstrated capacity of competitive segment Plant Capacity Plant Capacity Megawatt capacity of plants expected to be closed Megwatt Capacity for Retired Coal-Fired Power Plants Megwatt Capacity for Retired Coal-Fired Power Plants Regulated Independent Transmission Regulated Independent Transmission [Member] Regulated Independent Transmission. Other/Corporate Other Business Operations [Member] Other Business Operations [Member]. Reconciling Adjustments Reconciling Adjustments [Member] Reconciling Adjustments. Segment Financial Information Segment Financial Information Abstract Segment Financial Information. External revenues Revenue from External Customers Internal revenues Segment Reporting Information, Intersegment Revenue Total revenues Electric Revenue Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Investment income Investment Income, Interest and Dividend Net interest charges Interest Revenue (Expense), Net Income taxes Income Tax Expense (Benefit) Total assets Total goodwill Property additions Regulated Operations [Abstract] REGULATORY MATTERS Public Utilities Disclosure [Text Block] Investment excludes Receivables, Payables and Accrued income Investments Excludes Receivables Payables Deferred Taxes And Accrued Income Investments excludes receivables payables deferred taxes and accrued income. Cash balance excluded from available for sale securities Cash Receivables Payables Deferred Taxes Accrued Income Balance Excluded From Available For Sale Securities Cash receivables payables deferred taxes accrued income balance excluded from available for sale securities. Investments not required to be disclosed Investments not required to be disclosed Investments not required to be disclosed. Accounts, Notes, Loans and Financing Receivable by Receivable Type [Axis] Accounts, Notes, Loans and Financing Receivable by Receivable Type [Axis] Receivable Type [Domain] Receivable Type [Domain] Customer [Member] Customer [Member] Customer. Other [Member] Other Receivables [Member] Other receivables. Allowance for uncollectible accounts Allowance for Doubtful Accounts Receivable, Current Common stockholders' equity- Stockholders' Equity Attributable to Parent [Abstract] Common stock, par value Common Stock, Par or Stated Value Per Share Common Stock, No Par Value Common Stock, No Par Value Common stock, shares authorized Common Stock, Shares Authorized Common stock, shares outstanding Common Stock, Shares, Outstanding Income Tax Contingency [Table] Income Tax Contingency [Table] Allegheny Allegheny [Member] Allegheny. Income Tax Contingency [Line Items] Income Tax Contingency [Line Items] Decrease in unrecognized tax benefits Unrecognized Tax Benefits, Decreases Resulting from Current Period Tax Positions Unrecognized tax benefits expected to resolved within the next twelve month Unrecognized Tax Benefits Unrecognized benefits (if recognized) affecting effective tax rate Unrecognized Tax Benefits that Would Impact Effective Tax Rate Increase in accrued interest Unrecognized Tax Benefits, Interest on Income Taxes Expense Accrued Interest Unrecognized Tax Benefits, Interest on Income Taxes Accrued Change in effective tax rate as a result of non-deductible portion of merger transaction and integration costs Change in effective tax rate as a result of non deductible portion of merger transaction and integration costs Change in effective tax rate as a result of non-deductible portion of merger transaction and integration costs. SEGMENT INFORMATION Segment Reporting Disclosure [Text Block] Customers, net of allowance for uncollectible accounts Other, net of allowance for uncollectible accounts Materials and supplies Prepaid taxes Prepaid Taxes OTHER PROPERTY AND INVESTMENTS: Investments in lease obligation bonds Held-to-maturity Securities, Noncurrent Nuclear fuel disposal trust Nuclear Fuel Disposal Trust Nuclear Fuel Disposal Trust. Regulatory assets Regulatory Assets, Noncurrent Pension assets Prepaid Pension Costs Power purchase contract asset Power Purchase Contract Asset Power purchase contract asset. Intangible assets Intangible Assets, Net (Excluding Goodwill) Affiliated companies Short-term Non-bank Loans and Notes Payable Short-term borrowings Other Accounts payable Accounts Payable, Current Accrued taxes Accrued interest Interest Payable, Current Accrued compensation and benefits Accrued Employee Benefits, Current Customer deposits Customer Deposits, Current Lease market valuation liability Lease Market Valuation Liability Current Lease Market Valuation Liability Current. LIABILITIES RELATED TO ASSETS PENDING SALE (Note 15) Liabilities of Assets Held-for-sale Common stock Common Stock, Value, Outstanding Other paid-in capital Additional Paid in Capital, Common Stock Accumulated other comprehensive income Accumulated Other Comprehensive Income (Loss), Net of Tax Retained earnings (Accumulated deficit) Retained Earnings (Accumulated Deficit) Total common stockholders' equity Noncontrolling interest Stockholders' Equity Attributable to Noncontrolling Interest Total equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Accumulated deferred investment tax credits Accumulated Deferred Investment Tax Credit Adverse power contract liability Adverse Power Contract Liability Power purchase contract liability. Power purchase contract liability Power Purchase Contract Liability Power purchase contract liability. Nuclear fuel disposal costs Spent Nuclear Fuel Obligation, Noncurrent Derivatives Derivative Liabilities, Noncurrent COMMITMENTS, GUARANTEES AND CONTINGENCIES (Note 9) Commitments and Contingencies Related Party Transactions, by Related Party [Axis] Related Party [Domain] Affiliates Non-Affiliates Non-Affiliates [Member] Non-Affiliates. REVENUES: Revenues [Abstract] Electric utilities Electric Domestic Regulated Revenue Other Electric Revenue Other Electric revenue other. Unregulated businesses Electric Worldwide Unregulated Revenue Excise and gross receipts tax collections OPERATING EXPENSES: Costs and Expenses [Abstract] Fuel Fuel Costs Purchased power Cost of Purchased Power Other operating expenses Other Cost and Expense, Operating General taxes Taxes, Miscellaneous Impairment of long-lived assets Utilities Operating Expense, Impairments Total operating expenses Costs and Expenses OPERATING INCOME (LOSS) Operating Income (Loss) OTHER INCOME (EXPENSE): Other Nonoperating Income (Expense) [Abstract] Interest income Investment Income, Interest Miscellaneous income Other Nonoperating Income (Expense) Interest expense Interest and Debt Expense Capitalized interest Public Utilities, Allowance for Funds Used During Construction, Additions Total other income (expense) Nonoperating Income (Expense) INCOME BEFORE INCOME TAXES Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest INCOME TAXES (BENEFITS) NET INCOME Loss attributable to noncontrolling interest EARNINGS AVAILABLE TO FIRSTENERGY CORP. Net Income (Loss) Attributable to Parent EARNINGS PER SHARE OF COMMON STOCK: Basic Earnings Per Share, Basic Diluted Earnings Per Share, Diluted WEIGHTED AVERAGE NUMBER OF SHARES OUTSTANDING: Weighted Average Number of Shares Outstanding, Diluted [Abstract] Basic Weighted Average Number of Shares Outstanding, Basic Diluted Weighted Average Number of Shares Outstanding, Diluted DIVIDENDS DECLARED PER SHARE OF COMMON STOCK Common Stock, Dividends, Per Share, Declared COMMITMENTS, GUARANTEES AND CONTINGENCIES Commitments and Contingencies Disclosure [Text Block] Phantoms [Abstract] Phantoms [Abstract] Regulatory Matters [Table] Regulatory Matters [Table] Regulatory matters. Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Pending Litigation Pending or Threatened Litigation [Member] Target Period [Axis] Target Period [Axis] Target period. Target Period [Domain] Target Period [Domain] Target period. Year 2012 Year 2012 [Member] Year 2012. Year 2013 Year 2013 [Member] Year 2013 [Member] Statement, Geographical [Axis] Statement, Geographical [Axis] Segment, Geographical [Domain] Segment, Geographical [Domain] The Seneca Pumped Storage Project Relicensing Seneca Pumped Storage Project Relicensing [Member] The Seneca Pumped Storage Project Relicensing. OHIO OHIO MARYLAND MARYLAND PENNSYLVANIA PENNSYLVANIA WEST VIRGINIA WEST VIRGINIA California Claims Matters California Claims Matters [Member] California Claims Matters. Yards Creek Pumped Storage Project Yards Creek Pumped Storage Project [Member] Yards Creek Pumped Storage Project [Member] The Seneca Pumped Storage Project Seneca Pumped Storage Project [Member] The Seneca Pumped Storage Project Relicensing. Regulatory Matters [Axis] Regulatory Matters [Axis] Regulatory Matters. Regulatory Matters [Domain] Regulatory Matters [Domain] Regulatory Matters. FERC Ferc [Member] FERC Matters. Calculation Error [Axis] Calculation Error [Axis] Calculation Error. Calculation Error [Domain] Calculation Error [Domain] Calculation Error. PJM Calculation Error Pjm Calculation Error [Member] PJM Calculation Error. PATH Path [Member] PATH. City of New Martinsville City of New Martinsville [Member] City of New Martinsville [Member] Morgantown Energy Morgantown Energy [Member] Morgantown Energy [Member] Regulatory Matters [Line Items] Regulatory Matters [Line Items] Regulatory matters. Proposed electric consumption reduction percentage Proposed Electric Consumption Reduction Percentage Proposed electric consumption reduction percentage. Proposed electric demand reduction percentage Proposed Electric Demand Reduction Percentage Proposed electric demand reduction percentage. Expenditures for cost recovery program Expenditures For Cost Recovery Program Expenditures for cost recovery program. Maximum Amount Of Penalty Assessed Per Day Per Violation Maximum Amount Of Penalty Assessed Per Day Per Violation Maximum amount of penalty assessed per day per violation. Recovery period for expenditures for cost recovery program Recovery Period For Expenditures For Cost Recovery Program Recovery period for expenditures for cost recovery program. Load cap percentage minimum Load Cap Percentage Minimum Load cap percentage minimum. Maximum trance award to a single supplier Tranche Percentage, Maximum Award to Single Supplier Tranche Percentage, Maximum Award to Single Supplier Generation discount for low income customers Generation Discount For Low Income Customers Generation discount for low income customers. Costs avoided by customers, integration period Costs Avoided by Customers, Integration Period Costs Avoided by Customers, Integration Period Costs avoided by customers Costs Avoided By Customers Costs avoided by customers. Fund to assist low income customers Fund To Assist Low Income Customers Fund to assist low income customers. Legal Parties Legal Parties Legal Parties ESP extension term ESP Extension Term ESP Extension Term Annual energy savings Annual Energy Savings Annual Energy Savings Utilities required to reduce peak demand Utilities Required To Reduce Peak Demand Utilities required to reduce peak demand in 2009 in percentage. Utilities required to additionally reduce peak demand Utilities Required To Additionally Reduce Peak Demand -- None. No documentation exists for this element. -- Period of the portfolio plans filed seeking approval for the program Period of the portfolio plans filed seeking approval for the program Period of the portfolio plans filed seeking approval for the program. Reply Period in the Event of Motion Denial Reply Period in the Event of Motion Denial Reply Period in the Event of Motion Denial Application for Rehearing, Ruling Period Application for Rehearing, Ruling Period Application for Rehearing, Ruling Period Load served from renewable energy resources Load Served From Renewable Energy Resources Load Served From Renewable Energy Resources. Request for proposals conducted Request For Proposals Conducted Request For Proposals Conducted Marginal transmission refund period Marginal Transmission Refund Period Marginal Transmission Refund Period Marginal transmission losses Marginal Transmission Losses Marginal transmission losses. Minimum reduction in Utilities reduce energy consumption Minimum Reduction In Utilities Reduce Energy Consumption Minimum reduction in Utilities reduce energy consumption. Minimum reduction in Utilities peak demand Minimum Reduction In Utilities Peak Demand Minimum reduction in Utilities peak demand. Target installation smart meter Target installation smart meter Target installation smart meter. Grace period Grace period Grace period. Expenditure amortization period Expenditure Amortization Period Expenditure Amortization Period Parties Able to Challenge Recovery Amounts Parties Able to Challenge Recovery Amounts Parties Able to Challenge Recovery Amounts Directed Questions for Investigation Directed Questions for Investigation Directed Questions for Investigation Annualized base rate increase Annualized Base Rate Increase Annualized base rate increase. Storm restoration deferral period Storm Restoration Deferral Period Storm Restoration Deferral Period Additional base rate increase Additional Base Rate Increase Additional base rate increase. Decrease in ENEC rates Decrease In Enec Rates Decrease in Enec rates. Facilities Seeking Certification As Qualified Energy Resource Facilities Facilities Seeking Certification As Qualified Energy Resource Facilities Facilities Seeking Certification As Qualified Energy Resource Facilities Number of electric generation facilities Number of electric generation facilities Number of electric generation facilities. Number of electric generation facilities, owned by third party NUG Entity, Owned by Third Party, Contracted Resource NUG Entity, Owned by Third Party, Contracted Resource Power threshold for cost methodology Power Threshold For Cost Methodology Power Threshold For Cost Methodology Identified issues for written comments Identified Issues For Written Comments Identified Issues For Written Comments One time payment, ATSI agreed to MISO One Time Payment One time payment. Annual Revenue requirements in Zone Annual Revenue Requirements In Zone Annual Revenue Requirements In ATSI Zone related to Michigan Thumb Project. Losses incurred due to underfunding of contracts Losses Incurred Due to Underfunding of Contracts Losses Incurred Due to Underfunding of Contracts Settlement proposal claims Settlement Proposal Claims Settlement proposal claims. Court proceedings from filed claims Court Proceedings from Filed Claims Court Proceedings from Filed Claims New Voltage transmission facilities across PJM and a zonal transmission rate (In KV) New Voltage transmission facilities zonal transmission rate New Voltage transmission facilities zonal transmission rate Hydroelectric project Hydroelectric Project Capacity Hydroelectric Project Capacity Ownership interest Equity Method Investment, Ownership Percentage Renewal length of operating license Renewal Of Operating License Length RenewalOfOperatingLicenseLength ILP licensure period ILP Licensure Period ILP Licensure Period Period of cycle Period of Cycle Period of Cycle. Regional Enforcement Entities Regional Enforcement Entities Regional Enforcement Entities Customer Power Loss Period Customer Power Loss Period Customer Power Loss Period Net exposure to loss based upon the casualty value provisions Net Exposure To Loss Based Upon Casualty Value Provisions [Table Text Block] Net exposure to loss based upon the casualty value provisions. Document and Entity Information [Abstract] Document and Entity Information Abstract. Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Document Type Document Type Document Period End Date Document Period End Date Amendment Flag Amendment Flag Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Current Fiscal Year End Date Current Fiscal Year End Date Entity Well Known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Voluntary Filers Entity Current Reporting Status Entity Current Reporting Status Entity Filer Category Entity Filer Category Entity Common Stock Shares Outstanding Entity Common Stock, Shares Outstanding VARIABLE INTEREST ENTITIES Variable Interest Entities Disclosure [Text Block] Variable interest entities disclosure. PENSIONS AND OTHER POSTEMPLOYMENT BENEFITS Pension and Other Postretirement Benefits Disclosure [Text Block] Reconciliation of basic and diluted earnings per share of common stock Reconciliations Of Basic And Diluted Earnings Per Share Of Common Stock [Abstract] Reconciliations of Basic and Diluted Earnings Per Share of Common Stock. Weighted average number of basic shares outstanding Assumed exercise of dilutive stock options and awards Incremental Common Shares Attributable to Share-based Payment Arrangements Weighted average number of diluted shares outstanding Earnings available to FirstEnergy Corp. Basic Earnings Per Share of Common Stock Diluted Earnings Per Share of Common Stock Derivatives Not Designated As Hedging Instruments [Table] Derivatives Not Designated As Hedging Instruments [Table] Derivatives not designated as hedging instruments. Derivatives Not Designated As Hedging Instruments [Line Items] Derivatives Not Designated As Hedging Instruments [Line Items] Derivatives not designated as hedging instruments. Reconciliation of changes in the fair value of certain contracts that are deferred Reconciliation Of Changes In Fair Value Of Derivatives [Abstract] Reconciliation of changes in fair value of derivatives. Outstanding net asset (liability) [Roll Forward] Outstanding Net Asset (Liability) [Roll Forward] Outstanding Net Asset (Liability) [Roll Forward] Outstanding net asset (liability), Beginning Balance Derivatives Not Designated As Hedging Instruments At Fair Value Net Derivatives not designated as hedging instruments at fair value net. Additions/Change in value of existing contracts Derivative Instruments Not Designated As Hedging Instruments Additions Or Change In Value Of Existing Contracts Derivative instruments not designated as hedging instruments additions or change in value of existing contracts. Settled contracts Derivative Instruments Not Designated As Hedging Instruments Settled Contracts Settled Contracts. Outstanding net asset (liability), Ending Balance Consolidating Statements of Income Revenues OTHER INCOME (EXPENSE): Other Income Expense Abstract Other Income Expense Abstract. Miscellaneous income, including net income from equity investees INCOME (LOSS) BEFORE INCOME TAXES OTHER COMPREHENSIVE INCOME (LOSS): Other Comprehensive Income (Loss), Net of Tax [Abstract] Amortized loss on derivative hedges Other comprehensive income (loss) Other comprehensive income (loss), net of tax Segment Financial Information Schedule of Segment Reporting Information, by Segment [Table Text Block] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Table] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Table] Fair Value by Measurement Frequency [Axis] Fair Value by Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Recurring Fair Value, Measurements, Recurring [Member] Level 1 Fair Value, Inputs, Level 1 [Member] Level 2 Fair Value, Inputs, Level 2 [Member] Fair Value by Asset Class [Axis] Fair Value by Asset Class [Axis] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, by Asset Class [Domain] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, by Asset Class [Domain] Corporate debt securities Corporate Debt Securities [Member] Commodity contracts Commodity Contract [Member] Equity securities Equity Securities [Member] Foreign government debt securities Foreign Government Debt Securities [Member] U.S. government debt securities US Government Agencies Debt Securities [Member] U.S. state debt securities US Government-sponsored Enterprises Debt Securities [Member] Other Other Securities [Member] Other Securities. Interest Rate Swap Interest Rate Swap [Member] Fair Value by Liability Class [Axis] Fair Value by Liability Class [Axis] Fair Value, Liabilities, Measured on Recurring Basis, Unobservable Input Reconciliation, by Liability Class [Domain] Fair Value, Liabilities, Measured on Recurring Basis, Unobservable Input Reconciliation, by Liability Class [Domain] Fair Value Off Balance Sheet Risks By Financial Instrument [Axis] Fair Value, Off-balance Sheet Risks by Financial Instrument [Axis] Fair Value Off Balance Sheet Risks Financial Instruments [Domain] Fair Value, Off-balance Sheet Risks, Financial Instruments [Domain] Derivative Assets Derivative Assets [Member] Derivative Assets. Derivative Liabilities Derivative Liabilities [Member] Derivative Liabilities. Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Assets Assets, Fair Value Disclosure [Abstract] Fair value, assets Assets, Fair Value Disclosure Liabilities Liabilities, Fair Value Disclosure [Abstract] Fair value, liabilities Liabilities, Fair Value Disclosure Net assets (liabilities) Fair Value Of Assets And Liabilities Net Fair value of assets and liabilities net. Year 2020 Year 2020 [Member] Year 2020. Outstanding Guarantees [Axis] Outstanding Guarantees [Axis] Outstanding Guarantees [Axis] Outstanding Guarantees [Domain] Outstanding Guarantees [Domain] Outstanding Guarantees [Domain] Parental Guarantees Parent Company [Member] Subsidiaries' Guarantees Subsidiaries [Member] Other Guarantees Guarantee Type, Other [Member] Loss Contingencies by Nature of Contingency [Axis] Loss Contingencies by Nature of Contingency [Axis] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Caa Compliance Caa Compliance [Member] CAA Compliance. National Ambient Air Quality Standards National Ambient Air Quality Standards [Member] National Ambient Air Quality Standards. Hazardous Air Pollutant Emissions Hazardous Air Pollutant Emissions [Member] Hazardous Air Pollutant Emissions [Member] Climate Change Climate change [Member] Climate change. Loss Contingencies By Claims [Axis] Loss Contingencies By Claims [Axis] Loss Contingencies By Claims. Loss Contingencies By Claims [Domain] Loss Contingencies By Claims [Domain] Loss Contingencies By Claims. CAIR CAIR [Member] CAIR [Member] CSAPR CSAPR [Member] CSAPR [Member] Clean Water Act Clean Water Act [Member] Clean Water Act. Monongahela River Water Quality Monongahela River Water Quality [Member] Monongahela River Water Quality. Regulation of Waste Disposal Regulation Of Waste Disposal [Member] Regulation Of Waste Disposal. Nuclear Plant Matters Nuclear Plant Matters [Member] Nuclear Plant Matters. ICG Litigation ICG Litigation [Member] ICG Litigation [Member] Requirements [Axis] Requirements [Axis] Requirements. Requirements [Domain] Requirements [Domain] Requirements. Increase in funding Increase in funding [Member] Increase in funding. Signal Peak and Global Rail Signal Peak and Global Rail [Member] Signal Peak and Global Rail [Member] AE Supply and MP AE Supply and MP [Member] AE Supply and MP [Member] Outstanding guarantees and other assurances aggregated Guarantor Obligations, Current Carrying Value Surety bonds and related guarantees Surety Bonds And Related Guarantees Surety bonds and related guarantees. Company Posted Collateral Related To Net Liability Positions Company Posted Collateral Related To Net Liability Positions Company Posted Collateral Related To Net Liability Positions. Potential Collateral Posted Related to Net Liability Positions Potential Collateral Posted Related to Net Liability Positions Potential Collateral Posted Related to Net Liability Positions Signal Peak and Global Rail entered into a syndicated two-year senior secured term loan facility Senior Secured Term Loan Facility Senior secured term loan facility. Senior Secured Term Loan Facility, Term, Years Senior Secured Term Loan Facility, Term, Years Senior Secured Term Loan Facility, Term, Years Number of complaints filed against FGCO Power Plants Complaints Power plants complaints. Number of complaints seek enjoin plant Number of complaints seek enjoin plant Number of complaints seek enjoin plant. Number of individuals behalf of which complaint filed Number of individuals behalf of which complaint filed Number of individuals behalf of which complaint filed. Number of named plaintiffs as class representatives Number of named plaintiffs as class representatives Number of named plaintiffs as class representatives. Reduction in air emissions and compliance Percentage Of Reduction In Air Emission Percentage of reduction in air emission. Number of electric generation facilities Number of generation units Number of generation units Number of generation units. Number of phases under the EPA’s CAIR for reductions of Sulfur Dioxide and Mono-Nitrogen Oxides Phases Phases Capping of SO2 emissions (In Tons) Capping Of Gas One Emissions Capping Of S02 Emissions Capping of NOx emissions (In Tons) Capping of Gas Two emissions Capping of NOx emissions Capping of SO2 Emissions Under CSAPR Capping Of Gas One Emissions Under Cross State Air Pollution Rule Capping Of Gas One Emissions Under Cross State Air Pollution Rule Capping of NOx emissions under CSAPR Capping Of Gas Two Emissions Under Cross State Air Pollution Rule Capping Of Gas Two Emissions Under Cross State Air Pollution Rule Number of retired coal-fired plants being retired Retired Coal-Fired Power Plants, Total Retired Coal-Fired Power Plants, Total Megwatt Capacity for Retired Coal-Fired Power Plants Average percentage of power generation of retired coal-fired power plants Electricity Produced by Retired Coal-Fired Power Plants, Percent Electricity Produced by Retired Coal-Fired Power Plants, Percent Measurement period for power generation of retired coal-fired power plants Time Period for Retired Coal-Fired Power Plants Time Period for Retired Coal-Fired Power Plants Megawatt capacity for proposed combusion turbine Peaking Capacity Peaking Capacity Pre-tax severance expense related to closures Severance Costs Upper threshold limit for carbon dioxide emission (Tons per Year) Upper Threshold Limit For Carbon Di Oxide Emission Upper Threshold Limit For Carbon Di Oxide Emission Increase (Decrease) in Global Temperature Increase (Decrease) in Global Temperature Increase (Decrease) in Global Temperature Funds provided for Copenhagen Green Climate Fund Funds Provided For Copenhagen Green Climate Fund Funds Provided for Copenhagen Green Climate Fund. Annual percentage that fish impingement should be reduced to, per CWA Percentage Of Fish Impingement Percentage of fish impingement. Extension of comment period Extension of comment period Extension of Comment period. Maximum Capital Investment Required To Install Technology To Meet Tds And Sulfate Limits Maximum Capital Investment Required To Install Technology To Meet Tds And Sulfate Limits -- None. No documentation exists for this element. -- Portion of Monongahela River subject to CWA 303(d) Sulfate Impairment Designation For Approximately Mile Stretch Of River, Miles Sulfate Impairment Designation For Approximately Mile Stretch Of River, Miles TMDL Limit Development Period TMDL Limit Development Period TMDL Limit Development Period Number of days required prior to the filing of a citizen suit under notice Notice Letter Required Notice letter, required. Options proposed by EPA for additional regulation of coal combustion residuals Options Proposed By EPA Options Proposed By EPA Total environmental liabilities Accrual for Environmental Loss Contingencies Environmental Liabilities Former Gas Facilities Environmental Liabilities Former Gas Facilities Environmental Liabilities Former Gas Facilities. Decommissioning Fund Investments Parental guarantee associated with the funding of decommissioning costs Parental Guarantee Associated With Funding Of Decommissioning Costs Parental guarantee associated with funding of decommissioning costs. Request For Information from Number of Nuclear Power Plants, Total Request For Information from Number of Nuclear Power Plants, Total Request For Information from Number of Nuclear Power Plants, Total Renewal length of operating license for Davis-Besse Nuclear Power Station Loss incurred in damages for replacement coal purchased Loss incurred in damages for replacement coal purchased Loss incurred in damages for replacement coal purchased. Additional damages incurred for future shortfalls Additional damages incurred for future shortfalls Additional damages incurred for future shortfalls. Verdict in Favor Verdict in Favor Verdict in Favor Amount for which verdict entered for future damages Amount for which verdict entered for future damages Amount for which verdict entered for future damages. Amount for replacement coal and interest Amount for replacement coal and interest Amount for replacement coal and interest. Commitment Period by Developed Countries to Provide Funds, Years Commitment Period by Developed Countries to Provide Funds, Years Commitment Period by Developed Countries to Provide Funds, Years Potential MATS Extension Period Potential MATS Extension Period Potential MATS Extension Period Components of Net Periodic Benefit Costs Schedule of Net Benefit Costs [Table Text Block] Components of Net Periodic Benefit Costs Allocated to subsidiaries Net Periodic Pension And Other Post Employment Benefits Costs [Table Text Block] Net Periodic Pension and Other Post-Employment Benefits Costs. DERIVATIVE INSTRUMENTS Derivative Instruments and Hedging Activities Disclosure [Text Block] Net Periodic Pension and OPEB Costs (Credits) Net periodic benefit costs (credits) Defined Benefit Plan, Net Periodic Benefit Cost, Net of Capitalized Cost Defined Benefit Plan, Net Periodic Benefit Cost, Net of Capitalized Cost Condensed Consolidating Statements of Income and Comprehensive Income Supplemental Guarantor Condensed Consolidating Statements Of Income [Table Text Block] Condensed consolidating Statements of Income. Condensed Consolidating Balance Sheets Supplemental Guarantor Condensed Consolidating Balance Sheets [Table Text Block] Condensed consolidating balance sheets. Condensed Consolidating Statements of Cash Flows Supplemental Guarantor Condensed Consolidating Statements Of Cash Flows [Table Text Block] Condensed Consolidating Statements of Cash Flows. Schedule of Available for Sale Securities Major Types of Debt and Equity Securities [Axis] Schedule of Available-for-sale Securities, Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Domain] Major Types of Debt and Equity Securities [Domain] Amortized cost basis, unrealized gains and losses and fair values of investments in available-for-sale securities Available-for-sale Securities [Abstract] Cost Basis Available-for-sale Securities, Amortized Cost Basis Unrealized Gains Available-for-sale Securities, Gross Unrealized Gains Unrealized Losses Available-for-sale Securities, Gross Unrealized Losses Fair Value Available-for-sale Securities Derivative Instruments, Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk [Table] Derivative Instruments, Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk [Table] Derivative Instruments Gain Loss By Income Statement Location [Axis] Derivative Instruments, Gain (Loss) by Income Statement Location [Axis] Income Statement And Other Comprehensive Income Location [Domain] Income Statement and Other Comprehensive Income (Loss) Location [Domain] Purchase Power Expense Purchased Power Expense [Member] Purchased power expense. Revenue Revenue [Member] Revenue. Fuel Expense Fuel Expense Member Fuel expense. Other Operating Expense Other Operating Expense [Member] Derivative Instruments, Gain (Loss) [Line Items] Derivative Instruments, Gain (Loss) [Line Items] Effect of derivative instruments on the statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships Effect of derivative instruments on statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships [Abstract] Effect of derivative instruments on statements of income and comprehensive income for instruments designated in cash flow hedging relationships and not in hedging relationships. Hedging Relationship; Gain (Loss) Recognized in AOCL (Effective Portion) Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net Hedging Relationship Effective Gain (Loss) Reclassified to: Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net Not in a Hedging Relationship; Unrealized Gain (Loss) Recognized in: Not in a Hedging Relationship; Realized Gain (Loss) Reclassified to: Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net Public Utility [Axis] Public Utility [Axis] Utility Plant Domain Utility Plant [Domain] Oyster Creek Nuclear Generating Station Oyster Creek Nuclear Generating Station [Member] Oyster Creek Nuclear Generating Station Variable Interest Entities by Classification of Entity [Axis] Variable Interest Entities by Classification of Entity [Axis] Variable Interest Entity, Classification [Domain] Variable Interest Entity, Classification [Domain] Variable Interest Entity, Not Primary Beneficiary Variable Interest Entity, Not Primary Beneficiary [Member] PATH-WV Path Wv [Member] PATH-WV [Member]. Business Units [Axis] Business Units [Axis] Business units. Business Units [Domain] Business Units [Domain] Business Units. Signal Peak Signal Peak [Member] Signal Peak [Member] FEV FEV [Member] FEV [Member] PE PE [Member] PE. WP Wp [Member] WP. Power Purchase Agreements [Axis] Power Purchase Agreements [Axis] Power Purchase Agreements. Power Purchase Agreements [Domain] Power Purchase Agreements [Domain] Power Purchase Agreements. Power Purchase Agreements Power Purchase Agreements [Member] Power Purchase Agreements. Variable Interest Entities (Textuals) [Abstract] Variable Interest Entities (Textuals) [Abstract] Variable Interest Entities. Bondable stranded costs Long-term Transition Bond, Current Environmental control bond Long-term Pollution Control Bond Distributions to owners Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Joint venture, ownership percentage by parent Noncontrolling Interest, Ownership Percentage by Parent Percentage of high-voltage transmission line project owned by subsidiary of AE on the Allegheny Series Variable Interest Entities Percentage Of high voltage transmission line project owned By variable interest entity one in joint venture party one Variable interest entities percentage of high voltage transmission line project owned By variable interest entity one in joint venture party one. Percentage of high-voltage transmission line project owned by subsidiary of AE on the West Virginia Series Variable Interest Entities Percentage Of high voltage transmission line project owned By variable interest entity one in joint venture party two Variable Interest Entities Percentage of high voltage transmission line project owned By variable interest entity one in joint venture party two. Number of long-term power purchase agreements maintained by FirstEnergy with NUG entities Number of long term power purchase agreements maintained by parent company with Non utility generation entities Number of long term power purchase agreements maintained by parent company with Non utility generation entities. Number of contracts that may contain variable interest Number Of Variable Interest Contracts Number of variable interest contracts. Equity or debt invested in non-VIE NUG entities Investment In Variable Interest Entities Investment in variable interest entities. Reserve for adverse purchase power commitment Reserve For Adverse Purchase Power Commitment Reserve for adverse purchase power commitment. Current liability included in adverse purchase power commitment Current Liability Included In Adverse Purchase Power Commitment Current liability included in adverse purchase power commitment. Net present value of FirstEnergy's consolidated sale and leaseback operating lease commitments Operating Lease Commitments Net Present Value Operating lease commitments net present value.