Related Party Transactions [Abstract] Related Party Transactions [Abstract] Total Stockholders' Equity Beginning balance Ending balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Schedule of Capitalization, Equity [Table] Schedule of Capitalization, Equity [Table] Level 3 Level 3 Fair Value, Inputs, Level 3 [Member] Repurchase of partners' equity interest in VIE Adjustments to Additional Paid in Capital, Other Pending lawsuits Loss Contingency, Pending Claims, Number Fair value hierarchy for long-term debt Fair Value, by Balance Sheet Grouping Two [Table Text Block] Fair Value, by Balance Sheet Grouping Two Equity-based awards activity, net APIC, Share-based Payment Arrangement, Increase for Cost Recognition Revenue recognized Contract with Customer, Liability, Revenue Recognized Total current liabilities Current liabilities Liabilities, Current Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] Summary of NRG's Material Related Party Transactions Schedule of Related Party Transactions [Table Text Block] Impairment losses on investments Impairment losses on investments Other than Temporary Impairment Losses, Investments Capacity Capacity [Member] Total operating revenue Operating Revenues [Member] Operating Revenues [Member] Senior Notes, due 2028 Senior Notes due 2028 [Member] Senior Notes due 2028 Change in Cash from discontinued operations Net Cash Provided by (Used in) Discontinued Operations CONDENSED CONSOLIDATING STATEMENTS OF CASH FLOWS Condensed Cash Flow Statement [Table Text Block] Treasury stock, shares (in shares) Treasury shares, balance as of beginning of period (in shares) Treasury shares, balance as of end of the period (in shares) Treasury Stock, Shares Recent Accounting Developments New Accounting Pronouncements, Policy [Policy Text Block] Current Fiscal Year End Date Current Fiscal Year End Date Corporate Corporate Segment [Member] Offsetting of derivatives by counterparty assets Offsetting Assets [Table Text Block] Proceeds from issuance of common stock Proceeds from Issuance of Common Stock Total operating revenues Operating revenues Revenues Schedule of Capitalization [Table] Schedule of Capitalization [Table] Derivative [Line Items] Derivative [Line Items] West/Other West and Other [Member] West and Other Weighted average number of common shares outstanding — diluted (in shares) Weighted average number of common shares outstanding- dilutive (in shares) Weighted Average Number of Shares Outstanding, Diluted Entity Address, Postal Zip Code Entity Address, Postal Zip Code Transfers out of Level 3 Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Transfers out of Level 3 Carrying Amount Reported Value Measurement [Member] Credit Derivatives Contract Type [Domain] Credit Derivatives Contract Type [Domain] Emissions Emissions [Member] Details pertaining to the emission allowances, which is considered as a derivative commodity. Issuance of common stock Stock Issued During Period, Value, New Issues Credit agreement Line of Credit Facility, Maximum Borrowing Capacity (Loss)/income from discontinued operations per weighted average common share — diluted (in usd per share) Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Diluted Share Property, plant and equipment, net Property, Plant and Equipment, Net Bond obligation Third Party Bond Obligation Third Party Bond Obligation LIBOR London Interbank Offered Rate (LIBOR) [Member] Accumulated Other Comprehensive Loss AOCI Attributable to Parent [Member] Basis spread on variable rate Debt Instrument, Basis Spread on Variable Rate Commodity contracts current Commodity Contract Current [Member] The current portion of a derivative instrument whose primary underlying risk is tied to commodity prices. Nuclear decommissioning trust fund Debt Securities, Available-for-sale [Line Items] Counterparty Risk by Investment Grade [Axis] Counterparty Risk by Investment Grade [Axis] The counter party risk exposure by investment grades. Total Assets Assets Entity Shell Company Entity Shell Company Cover page. Cover [Abstract] Document Type Document Type Reconciliation of beginning and ending balances for financial instruments that are recognized at fair value in the consolidated financial statements at least annually using significant unobservable inputs Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Unrealized Losses Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax Subsequent Event Subsequent Event [Member] Environmental Matters Environmental Loss Contingency Disclosure [Text Block] Loss Contingencies Loss Contingencies [Line Items] Variable Rate [Domain] Variable Rate [Domain] Schedule of Stock by Class, Equity [Roll Forward] Schedule of Stock by Class, Equity [Roll Forward] Schedule of Stock by Class, Equity [Roll Forward] Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative Instruments and Hedging Activities Disclosure [Abstract] South Central Portfolio South Central Portfolio [Member] South Central Portfolio [Member] Current Liabilities Liabilities, Current [Abstract] Credit Facility [Axis] Credit Facility [Axis] Lignite Contract With Texas Westmoreland Coal Co. Lignite Contract With Texas Westmoreland Coal Co. [Member] Lignite Contract With Texas Westmoreland Coal Co. [Member] Unrecorded Unconditional Purchase Obligation by Category of Item Purchased [Axis] Unrecorded Unconditional Purchase Obligation by Category of Item Purchased [Axis] Foreign government fixed income securities Debt Security, Government, Non-US [Member] Pension plan employer contributions deferred until 2021 Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year Estimated future fixed fee performance obligations Revenue, Remaining Performance Obligation, Amount Redeemable noncontrolling interest Redeemable Noncontrolling Interest, Equity, Carrying Amount Financial Instrument [Axis] Financial Instrument [Axis] Segment Reporting Segment Reporting Disclosure [Text Block] Equity [Abstract] Equity [Abstract] Nuclear Decommissioning Nuclear Decommissioning [Policy Text Block] Describes an entity's policy regarding nuclear decommissioning trust fund assets and compliance with regulatory treatment. Intercompany dividends and transfers Intercompany Dividend Proceeds - Financing Intercompany Dividend Proceeds - Financing Segment Reporting Information Segment Reporting Information [Line Items] Document Quarterly Report Document Quarterly Report Commitments and Contingencies Commitments and Contingencies Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Condensed Consolidating Financial Information Disclosure [Abstract] Condensed Consolidating Financial Information Disclosure [Abstract] -- None. No documentation exists for this element. -- Debt Instrument [Line Items] Debt Instrument [Line Items] Consolidation Items [Domain] Consolidation Items [Domain] Nuclear trust fund investments Decommissioning Fund Investments Disposal Group Classification [Axis] Disposal Group Classification [Axis] Capital Allocation Plan [Axis] Capital Allocation Plan [Axis] Explains the different capital allocation plans. Operating costs and expenses Disposal Group, Including Discontinued Operation, Operating Expense Energy revenue Energy Revenue [Member] Energy Revenue [Member] Proceeds from sale of assets, net of cash disposed and sale of discontinued operations, net of fees Proceeds From Sale Of Assets And Sale Of Discontinued Operations, Net Proceeds from Sale Of Assets And Sale Of Discontinued Operations, Net Federal agency mortgage-backed securities Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] Total accounts receivable, net Accounts Receivable, after Allowance for Credit Loss Entity File Number Entity File Number Equity in earnings of consolidated subsidiaries Equity in Earnings of Consolidated Subsidiaries This item represents the proportionate share of the parent in the earnings of the consolidated subsidiaries. Revenue remaining performance obligation period Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Other Proceeds from (Payments for) Other Financing Activities Treasury Stock Treasury Treasury Stock [Member] Capital Allocation Plan Capital Allocation Plan [Member] Capital Allocation Plan [Member] Unrealized gain (loss) from open economic hedge positions Unrealized Gain (Loss) on Cash Flow Hedging Instruments Segments [Axis] Segments [Axis] Document Fiscal Period Focus Document Fiscal Period Focus Financial Instruments [Domain] Financial Instruments [Domain] Treasury stock, at cost - 177,356,039 and 172,894,601 shares at March 31, 2020 and December 31, 2019, respectively Treasury Stock, Value Period of estimated counterparty credit risk exposure, years Estimated Counterparty Credit Risk Exposure to Certain Counterparties, Period Estimated Counterparty Credit Risk Exposure to Certain Counterparties, Period Product and Service [Domain] Product and Service [Domain] Intercompany dividends Intercompany Dividend Proceeds - Investing Intercompany Dividend Proceeds - Investing Coal Coal [Member] Gain on disposal of discontinued operations, net of tax Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax Financial Information for Consolidated VIEs Schedule of Variable Interest Entities [Table Text Block] Income from discontinued operations, net of income tax Gain from discontinued operations, net of tax Income from discontinued operations, net of tax Income from discontinued operations Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent Diluted income per share: Earnings Per Share, Diluted [Abstract] Common stock dividends proposed annual amount (in usd per share) Common Stock, Dividends, Proposed Annual Amount, Per Share Common Stock, Dividends, Proposed Annual Amount, Per Share Derivative revenue Total unrealized gains Unrealized Gain (Loss) on Derivatives Operating Income/(Loss) Operating Income (Loss) Investment grade External Credit Rating, Investment Grade [Member] Beginning balance Ending balance Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs Derivatives by Underlying Assets [Axis] Derivatives by Underlying Assets [Axis] Derivatives by the underlying asset from which its value is derived. Goodwill Goodwill Gross Amounts of Recognized Assets / Liabilities Fair Value of Gross Derivative Assets/(Liabilities), Net Fair value of gross derivative assets less fair value of gross derivative liabilities. Segments [Domain] Segments [Domain] Statement [Line Items] Statement [Line Items] Hedging Designation [Domain] Hedging Designation [Domain] Revenue from contracts with customers Revenue from Contract with Customer, Excluding Assessed Tax Disaggregation of Revenue from Contracts with Customer Disaggregation of Revenue [Table Text Block] Other Comprehensive Loss Other Comprehensive Loss Other Comprehensive Income (Loss), Net of Tax [Abstract] Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Earnings/Loss per Weighted Average Common Share — Basic (in usd per share) Income/(loss) per weighted average common share — basic (in usd per share) Earnings Per Share, Basic Common stock dividends declared (in usd per share) Common Stock, Dividends, Per Share, Declared Comprehensive Income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Long-term capital allocation, target allocation, cash generated allocated to growth investments, percentage Long-term Capital Allocation, Target Allocation, Cash Generated Allocated to Growth Investments, Percentage Long-term Capital Allocation, Target Allocation, Cash Generated Allocated to Growth Investments, Percentage Subsequent Event Type [Axis] Subsequent Event Type [Axis] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Derivative Instruments Derivative Asset, Fair Value, Gross Liability XOOM Energy Litigation XOOM Energy Litigation [Member] XOOM Energy Litigation Cash provided by discontinued operations Cash Provided by (Used in) Financing Activities, Discontinued Operations Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Amendment Flag Amendment Flag Discontinued Operations and Disposal Groups [Abstract] Discontinued Operations and Disposal Groups [Abstract] Texas TEXAS Common stock, shares outstanding (in shares) Outstanding, as of beginning of period (in shares) Outstanding, as of end of period (in shares) Common Stock, Shares, Outstanding Nuclear Decommissioning Trust Fund Nuclear Decommissioning Trust Fund [Text Block] This item represents the disclosure regarding the nuclear decommissioning trust fund assets investments held in trust to pay for the cost of decommissioning a facility at the end of its economic life as a single block text. The disclosure may include the following: the aggregate fair values and unrealized gains and losses (including other-than-temporary impairments) for the securities held as well as information about the contractual maturities of those securities; summarized proceeds from sales of available for sale securities and the related realized gains and losses from these sales. The disclosure also includes that such funds are contributed and owned by the ratepayers but reported by the entity. Level 1 Fair Value, Inputs, Level 1 [Member] Customer [Axis] Customer [Axis] Consolidation Items [Axis] Consolidation Items [Axis] Activity in Allowance for Credit Losses Accounts Receivable, Allowance for Credit Loss [Table Text Block] Interest expense Interest Expense Total other liabilities Liabilities, Noncurrent CONDENSED CONSOLIDATING STATEMENTS OF COMPREHENSIVE INCOME /(LOSS) Condensed Statement of Comprehensive Income [Table Text Block] Power Power [Member] Details pertaining to the power, which is considered as a derivative commodity. Cash received Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Settlements Percentage of ownership sold Percentage of Ownership Sold of Subsidiary Percentage of Ownership Sold of Subsidiary Changes in Capital Structure Stockholders' Equity Note Disclosure [Text Block] Total retail revenue Products And Services, Total Retail [Member] Products And Services, Total Retail [Member] Regulatory Matters Regulatory Matters [Text Block] Describes all of the specific regulatory matters that are pending, including the regulatory authorities involved and the potential impacts. Use of Estimates Use of Estimates, Policy [Policy Text Block] Adequate Assurance Clauses Adequate Assurance Clauses [Member] Adequate Assurance Clauses [Member] Midway-Sunset Midway-Sunset Cogeneration Company [Member] Midway-Sunset Cogeneration Company [Member] Ivanpah Ivanpah [Member] Ivanpah [Member] Underlying Asset Class [Axis] Underlying Asset Class [Axis] Total other assets Regulated Entity, Other Assets, Noncurrent Equity in losses of unconsolidated affiliates Equity in losses of unconsolidated affiliates Income (Loss) from Equity Method Investments (Gain)/loss on sale of assets and disposal of assets Net loss on sale of assets and disposal of assets Gain (Loss) on Disposition of Assets Local Phone Number Local Phone Number Weighted-average Maturities (In years) Decommissioning Trust Assets, Weighted Average Maturity Period The weighted-average maturity period for securities of nuclear decommissioning trust funds assets. Discontinued Operations and Dispositions Disposal Groups, Including Discontinued Operations, Disclosure [Text Block] Derivative revenue Products And Services, Derivative Revenue [Member] Products And Services, Derivative Revenue [Member] Accounts receivable, net Accounts receivable, net Accounts Receivable, after Allowance for Credit Loss, Current Position [Domain] Position [Domain] Position [Axis] Position [Axis] Depreciation and amortization Depreciation and amortization Depreciation, Amortization and Accretion, Net Property, Plant and Equipment [Abstract] Property, Plant and Equipment [Abstract] Total other income/(expense) Nonoperating Income (Expense) Debt and Finance Leases Long-term Debt [Text Block] Credit Rating Contingent Features Credit Rating Contingent Features [Member] Credit Rating Contingent Features [Member] Nature of Business and Basis of Presentation Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Nuclear decommissioning trust liability Nuclear Decommissioning Trust Fund Liability Noncurrent The company is a beneficiary of a trust funded through collections from electric utility ratepayers. In the event that the trust funds are ultimately determined to be inadequate to decommission the company's nuclear facility, all additional amounts required to fund the decommissioning obligations may be collected through non-by-passable charges to the ratepayers. Following the completion of the decommissioning, if surplus funds remain in the decommissioning trusts, any excess funds will be refunded to the respective ratepayers. Consequently, the liability represents a liability to ratepayers in the state of Texas related to decommissioning of the company's Texas nuclear facility. This liability is the sum of the nuclear decommission trust fund asset, the nuclear decommissioning retirement obligation asset included within property, plant and equipment, less the nuclear decommissioning reserve. The total carrying value of all assets and liabilities associated with the decommissioning and the trusts net to zero and none of the activities related to the decommissioning of the STP nuclear facility are recorded in the income statement as ultimately the ratepayers in the state of Texas are liable for decommissioning the facility. Equity securities Equity Securities [Member] Fair Value Option, Quantitative Disclosures [Line items] Fair Value, Option, Quantitative Disclosures [Line Items] Net purchases of emission allowances Net purchases of /proceeds from emission allowances Payments For Proceeds From Intangible Assets Payments For Proceeds From Intangible Assets Prepayments and other current assets Prepaid Expense and Other Assets, Current Defined benefit plans Defined benefit plans, net Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Letters of credit issued Letters of credit issued Letters of Credit Outstanding, Amount Lease renewal term Lessee, Operating Lease, Renewal Term Total current assets Current assets Assets, Current Entity Current Reporting Status Entity Current Reporting Status Operating revenues Disposal Group, Including Discontinued Operation, Revenue Income from continuing operations per weighted average common share — basic (in usd per share) Income (Loss) from Continuing Operations, Per Basic Share Commodity contracts long-term Commodity Contract Non Current [Member] The noncurrent portion of a derivative instrument whose primary underlying risk is tied to commodity prices. Net Increase in Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Distributions from and equity in losses of unconsolidated affiliates Income (Loss) from Equity Method Investments, Net of Dividends or Distributions Other Liabilities Other Liabilities Liabilities, Noncurrent [Abstract] Net Income (Loss) Net income available to common shareholders Net (loss)/income Net Income/(Loss) Net Income (Loss) Attributable to Parent Effective Tax Rate Effective Income Tax Rate Reconciliation, Percent [Abstract] Liabilities Liabilities, Fair Value Disclosure [Abstract] Other Other [Member] Other [Member] Common Stock Common Stock Common Stock [Member] Cash used by discontinued operations Cash provided by (Used) discontinued operations Cash Provided by (Used in) Investing Activities, Discontinued Operations Current Assets Assets, Current [Abstract] Tax-exempt bonds Tax-exempt Bonds [Member] Tax-exempt Bonds [Member] Operating Costs and Expenses Operating Costs and Expenses [Abstract] Employee Stock Purchase Plan, minimum percentage of eligible compensation to purchase shares Employee Stock Purchase Plan, Minimum Percentage of Compensation Eligible Employee Stock Purchase Plan, Minimum Percentage of Compensation Eligible Debt Instrument [Axis] Debt Instrument [Axis] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Amortization of financing costs and debt discount/premiums Amortization of Debt Issuance Costs and Discounts Condensed Financial Statements, Captions [Line Items] Condensed Financial Statements, Captions [Line Items] Jointly Owned Utility Plant [Axis] Jointly Owned Utility Plant [Axis] Fair Value, Balance Sheet Grouping, Financial Statement Captions Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Net Income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Product and Service [Axis] Product and Service [Axis] Accounts receivable, net - Affiliate Affiliated Entity [Member] Entity Small Business Entity Small Business Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Gains (losses) for the period included in earnings attributable to the change in unrealized gains or losses relating to assets or liabilities still held Fair Value, Net Derivative Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss) Entity Filer Category Entity Filer Category CONDENSED CONSOLIDATING STATEMENTS OF OPERATIONS Condensed Income Statement [Table Text Block] Income from continuing operations per weighted average common share — diluted (in usd per share) Income (Loss) from Continuing Operations, Per Diluted Share Letter of Credit Letter of Credit [Member] Accrued expenses and other current liabilities Other Accrued Liabilities, Current Other expense Disposal Group, Including Discontinued Operation, Other Expense Total Liabilities and Stockholders' Equity Liabilities and Equity Other Assets Assets, Noncurrent [Abstract] Condensed Consolidating Financial Information Condensed Financial Information of Parent Company Only Disclosure [Text Block] Entity Address, City or Town Entity Address, City or Town Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Receivable Type [Axis] Receivable Type [Axis] Cash and cash equivalents Cash and cash equivalents Cash and Cash Equivalents [Member] Current portion of long-term debt Long-term Debt, Current Maturities Long-term Debt, Current Maturities Loss Contingencies [Table] Loss Contingencies [Table] Non-current operating lease liabilities Operating Lease, Liability, Noncurrent Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Restricted cash Restricted Cash and Cash Equivalents, Current Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Table] Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Table] Corporate debt securities Corporate Debt Securities [Member] Stockholders' Equity Stockholders' Equity Attributable to Parent [Abstract] Document Fiscal Year Focus Document Fiscal Year Focus Condensed Financial Statements [Table] Condensed Financial Statements [Table] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Capacity revenue Capacity Revenue [Member] Capacity Revenue [Member] Proceeds from the sale of nuclear decommissioning trust fund securities Proceeds from sale of securities Proceeds from Sale of Debt Securities, Available-for-sale Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Estimated carrying amounts and fair values of NRG's recorded financial instruments not carried at fair market value Fair Value, by Balance Sheet Grouping [Table Text Block] Operating Revenues Revenues [Abstract] Litigation Case [Domain] Litigation Case [Domain] Long-term debt Schedule of Debt [Table Text Block] Common stock, annual dividend growth rate, percentage Common Stock, Annual Dividend Growth Rate Common Stock, Annual Dividend Growth Rate Changes in nuclear decommissioning trust liability Changes in Nuclear Decommissioning Trust Liability The net change during the reporting period in the nuclear decommissioning trust liability, representing amounts collected, through rates or other authorized charges to electric utility customers, which are designated for funding the Company's portioning of the decommissioning of its nuclear facilities. Following the completion of the decommissioning, if surplus funds remain in the decommissioning trusts, any excess will be refunded to the respective rate payers. Senior Secured First Lien Notes, due 2029 Senior Secured First Lien Notes, Due 2029 [Member] Senior Secured First Lien Notes, Due 2029 [Member] Award Type [Axis] Award Type [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Cost of operations Cost of Revenue Eliminations Consolidation, Eliminations [Member] Average price paid per share (in usd per share) Treasury Stock Acquired, Average Cost Per Share Environmental Matters Disclosure [Abstract] Environmental Matters Disclosure [Abstract] -- None. No documentation exists for this element. -- Common stock dividends Dividends, Common Stock, Cash Derivative Instruments Derivative Liability, Fair Value, Gross Asset Other income, net Other Nonoperating Income (Expense) Class of Stock [Line Items] Class of Stock [Line Items] Schedule of Equity Method Investments [Table] Schedule of Equity Method Investments [Table] Other Balance Sheet Information Supplemental Balance Sheet Disclosures [Table Text Block] Supplemental Balance Sheet Disclosures Related Party Transactions Related Party Transactions Disclosure [Text Block] Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Other (Expense)/Income Costs and Expenses [Abstract] Commodity contracts Commodity Contract [Member] Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Power Contracts Power Contracts [Member] Power Contracts [Member] Amounts paid for shares purchased Stock Repurchased During Period, Value Net Amount Derivative Asset, Fair Value, Amount Offset Against Collateral Retail revenue Products And Services, Retail Revenue [Member] Products And Services, Retail [Member] Net income Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest Accumulated Deficit Retained Earnings [Member] Schedule of Capitalization, Equity [Line Items] Schedule of Capitalization, Equity [Line Items] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event [Line Items] Subsequent Event [Line Items] Regulatory Matters Disclosure [Abstract] Regulatory Matters Disclosure [Abstract] -- None. No documentation exists for this element. -- Impairments Asset Impairment Charges [Text Block] Document Period End Date Document Period End Date Statement [Table] Statement [Table] Entity Registrant Name Entity Registrant Name Investment, Name [Domain] Equity Method Investee, Name [Domain] Investment, Name [Domain] Commercial mortgage-backed securities Commercial Mortgage Backed Securities [Member] Other revenue, derivative Products And Services, Other Derivative Revenue [Member] Products and Services, Other Derivative Revenue [Member] Investments in nuclear decommissioning trust fund securities Investments in nuclear decommissioning trust fund securities Payments to Acquire Debt Securities, Available-for-sale Other trust fund investments: Other Trust Fund Investments [Abstract] Other Trust Fund Investments Deferred revenues Contract with Customer, Liability Other comprehensive (loss) income Other Comprehensive Income (Loss), Net Of Tax And Adjustment For New Accounting Standard Other Comprehensive Income (Loss), Net Of Tax And Adjustment For New Accounting Standard Variable Interest Entity, Primary Beneficiary Variable Interest Entity, Primary Beneficiary [Member] (Loss)/income from discontinued operations per weighted average common share — basic (in usd per share) Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic Share Reversal of acquired loss/(gain) positions related to economic hedges Reversal Previously Recognized, Unrealized Gains (Losses) Acquired as Part of Acquisition Economic Hedges Amount reversed into entity's statement of operations for previously recognized unrealized (gains) losses on settled positions related to acquired economic hedges. NRG Energy, Inc. (Note Issuer) Parent Company [Member] Financial institutions Financial Institutions [Member] Represents the information pertaining to the financial institutions. Assets and liabilities measured and recorded at fair value on the consolidated balance sheets on a recurring basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Cash Flows from Investing Activities Net Cash Provided by (Used in) Investing Activities [Abstract] Cash provided/(used) by continuing operations Net Cash Provided by (Used in) Operating Activities, Continuing Operations High Maximum Maximum [Member] Revolver Facility Credit Agreement [Member] Credit Agreement [Member] East East [Member] East Related Party [Domain] Related Party [Domain] Changes in derivative instruments Increase (Decrease) in Derivative Assets and Liabilities Investments in securities (classified within other current and non-current assets) Debt Securities, Available-for-sale Senior Secured First Lien Notes, due 2024 Senior Secured First Lien Notes, Due 2024 [Member] Senior Secured First Lien Notes, Due 2024 [Member] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Accumulated deficit Retained Earnings (Accumulated Deficit) Reversal of previously recognized unrealized losses on settled positions related to economic hedges Reversal Previously Recognized, Unrealized Gains (Losses) Settled Positions, Economic Hedges Amount reversed into entity's statement of operations for previously recognized unrealized (gains) losses on settled positions related to economic hedges. Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] Non Recourse Debt Non Recourse Debt [Member] Represents the non-recourse debt. Operating revenues Sales [Member] Entity Tax Identification Number Entity Tax Identification Number Debt issuance amount Debt Instrument, Face Amount Measured using net asset value practical expedient: Measured Using Net Asset Value Practical Expedient [Abstract] Measured Using Net Asset Value Practical Expedient Earnings/(Loss) per Weighted Average Common Share — Diluted (in usd per share) Income/(loss) per weighted average common share — diluted (in usd per share) Earnings Per Share, Diluted Uncertain tax benefits, penalties and interest accrued Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued Jointly Owned Utility Plant [Domain] Jointly Owned Utility Plant [Domain] Trading Symbol Trading Symbol Low Minimum Minimum [Member] U.S. government and federal agency obligations Financial Instruments, Owned, US Government and Agency Obligations, at Fair Value Renewable Energy Certificates Renewable Energy Certificates [Member] Renewable Energy Certificates [Member] Reconciliation of Cash and Cash Equivalents, Restricted Cash and Funds Deposited by Counterparties Restrictions on Cash and Cash Equivalents [Table Text Block] Foreign currency translation adjustments Foreign currency translation adjustments, net Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Long Long [Member] Statistical Measurement [Domain] Statistical Measurement [Domain] Adjustments to reconcile net income to cash provided by operating activities: Adjustments to reconcile net income/(loss) to cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Collateral due on net liability position that has not been called by a certain marginable agreement counterparty Derivative, Net Liability Position, Aggregate Fair Value Lease and easement agreement, number of extensions Lease And Easement Agreement, Number Of Extensions Lease And Easement Agreement, Number Of Extensions Recourse Debt Recourse Debt [Member] Recourse Debt [Member] Counterparty Risk by Institution [Axis] Counterparty Risk by Institution [Axis] The counter party risk exposure by institutions involved. Net Cash Provided/(Used) by Financing Activities Net Cash Provided by (Used in) Financing Activities Investments Accounted for Using the Equity Method and Variable Interest Entities, or VIEs Additional Financial Information Disclosure [Text Block] Investment in subsidiaries Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures Summary of aggregate fair values and unrealized gains and losses (including other-than-temporary impairments) for the securities held in the nuclear decommissioning trust fund Decommissioning Trust Assets [Table Text Block] Disclosure related to investments held in a trust fund to pay for the costs of decommissioning facilities. Income tax expense Income tax expense from continuing operations Income tax expense Income Tax Expense (Benefit) Mark-to-market for economic hedging activities Total unrealized mark-to-market gains for economic hedging activities Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities Amortization of nuclear fuel Amortization of Power Contracts Emission Credits Counterparty credit risk exposure to certain counterparties, threshold (as a percent) Counterparty Credit Risk Exposure, Percentage Threshold Represents the threshold percentage for disclosure of counterparty credit exposure. Derivative liabilities Derivative Liabilities Derivative liabilities Derivative Liability, Fair Value, Gross Liability Revenue from Contract with Customer [Abstract] Revenue from Contract with Customer [Abstract] Other non-current liabilities Other Liabilities, Noncurrent Guarantor Subsidiaries Guarantor Subsidiaries [Member] Counterparty Risk by Investment Grade [Domain] Counterparty Risk by Investment Grade [Domain] Represents the counter party risk exposure by investment grades. City Area Code City Area Code Business Solutions customers Business Solutions Customers [Member] Business Solutions Customers [Member] Title of 12(b) Security Title of 12(b) Security Other Other Payments for (Proceeds from) Other Investing Activities Related Party [Axis] Related Party [Axis] Shares issued to employee accounts (in shares) Stock issued under ESPP (in shares) Stock Issued During Period, Shares, Employee Stock Purchase Plans Total assets Assets, Fair Value Disclosure Net distributions from investments in unconsolidated affiliates Net distributions from investments in unconsolidated affiliates (Investments in) Proceeds From Sales of Unconsolidated Affiliates (Investments in) Proceeds From Sales of Unconsolidated Affiliates Fair Value Estimate of Fair Value Measurement [Member] Derivative net liability position, collateral required for contracts with credit rating contingent feature Collateral Already Posted, Aggregate Fair Value Significant unobservable inputs used developing fair values, Quantitative Information Fair Value Measurement Inputs and Valuation Techniques [Table Text Block] Earnings per Share Earnings Per Share [Abstract] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Gain on sale of assets Gain (Loss) on Disposition of Other Assets Derivative instruments Derivative Liability, Current Deferred income taxes Deferred Income Tax Assets, Net Convertible Senior Notes, due 2048 Convertible Senior Notes Due 2048 [Member] Convertible Senior Notes due 2048 [Member] Dunkirk Power LLC Tax Exempt Bonds Due 2042 Dunkirk Power LLC Tax Exempt Bonds Due 2042 [Member] Represents Dunkirk Power LLC tax exempt bonds, which are due 2042. Shares Repurchased Class of Treasury Stock [Table Text Block] Forward Market Price (per MWh) Derivative, Forward Price Income from Continuing Operations Before Income Taxes Income/(loss) from continuing operations before income taxes Income from continuing operations before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Fair Value Measurement Inputs and Valuation Techniques [Table] Fair Value Measurement Inputs and Valuation Techniques [Table] ASSETS Assets [Abstract] Unrealized Gains Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax Gain on sale of assets Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal Reversal of previously recognized unrealized (gains) on settled positions related to trading activity Reversal Previously Unrecognized, Unrealized Gains (Losses) Settled Positions Trading Activity Amount reversed into entity's statement of operations for previously recognized unrealized (gains) losses on settled positions related to trading activities. Employee Stock Purchase Plan, exercise price as percentage of fair value Employee Stock Purchase Plan, Exercise Price as Percentage of Fair Value This element represents the exercise price under employee stock purchase plan as a percentage of fair value. Discounts Debt Instrument, Unamortized Discount (Premium), Net Net Amount Derivative Liability, Fair Value, Amount Offset Against Collateral Proceeds from issuance of long-term debt Proceeds from Issuance of Debt Accretion of asset retirement obligations Accretion Expense, Including Asset Retirement Obligations Cash Flows from Operating Activities Net Cash Provided by (Used in) Operating Activities [Abstract] Lease revenue Operating Lease, Lease Income Petra Nova Petra Nova [Member] Petra Nova Nuclear decommissioning trust fund Fair Value Decommissioning Fund Investments, Fair Value Cash collateral received in support of energy risk management activities Cash Collateral (Held) / Posted Derivative, Collateral, Obligation to Return Cash Cash provided by discontinued operations Cash provided by discontinued operations Cash Provided by (Used in) Operating Activities, Discontinued Operations Capital Allocation Plan, Open Market Repurchases Capital Allocation Plan, Open Market Repurchases [Member] Capital Allocation Plan, Open Market Repurchases Derivative instruments Derivative Instruments and Hedges, Assets Schedule of segment reporting information, by segment Schedule of Segment Reporting Information, by Segment [Table Text Block] Segment Reporting [Abstract] Segment Reporting [Abstract] Credit Derivatives Contract Type [Axis] Credit Derivatives Contract Type [Axis] Impairment losses Equity Method Investment, Other than Temporary Impairment Deferred customer acquisition costs Capitalized Contract Cost, Net Measurement Basis [Axis] Measurement Basis [Axis] Long-term capital allocation, target allocation, cash generated allocated returned to shareholders, percentage Long-term Capital Allocation, Target Allocation, Cash Generated Allocated Returned to Shareholders, Percentage Long-term Capital Allocation, Target Allocation, Cash Generated Allocated Returned to Shareholders, Percentage Equity securities — nuclear trust fund investments Equity Securities-Nuclear Trust Fund [Member] Equity Securities-Nuclear Trust Fund [Member] Intangible assets, net Intangible assets, net Finite-Lived Intangible Assets, Net Discontinued Operations, Disposed of by Sale Discontinued Operations, Disposed of by Sale [Member] Customer [Domain] Customer [Domain] Debt Disclosure [Abstract] Debt Disclosure [Abstract] Cash consideration Disposal Group, Including Discontinued Operation, Consideration Derivative, nonmonetary notional amount, mass (ton) Derivative, Nonmonetary Notional Amount, Mass Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Instrument [Axis] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Income Statement Location [Domain] Income Statement Location [Domain] Statistical Measurement [Axis] Statistical Measurement [Axis] Natural Gas Natural Gas [Member] Details pertaining to the natural gas, which is considered as a derivative commodity. Fair Value Inputs / Range Fair Value Measurement Inputs and Valuation Techniques [Abstract] Income from Continuing Operations Income/(loss) from continuing operations Income from continuing operations Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at Beginning of Period Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at End of Period Cash and cash equivalents, funds deposited by counterparties and restricted cash shown in the statement of cash flows Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations Credit Agreement Credit Agreement 2019 [Member] Credit Agreement 2019 [Member] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Net counterparty credit exposure to a portion of the Company's counterparties Net Credit Exposure Represents the net exposure of the entity determined as total credit exposure to all counterparties less collateral (cash and letters of credit) held against those positions as of the reporting date. Shares repurchased (in shares) Total number of shares purchased (in shares) Stock Repurchased During Period, Shares Basic income per share: Earnings Per Share, Basic [Abstract] Payments of dividends to common stockholders Payments of Ordinary Dividends, Preferred Stock and Preference Stock Economic interest in equity method investments (as a percent) Equity Method Investment, Ownership Percentage Net proceeds from notes receivable Proceeds from Collection of Notes Receivable Total (losses)/gains — realized/unrealized included in earnings Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings Write-offs Accounts Receivable, Allowance for Credit Loss, Writeoff Investment, Name [Axis] Equity Method Investee, Name [Axis] Investment, Name [Axis] Common stock, shares authorized (in shares) Common Stock, Shares Authorized Intangible assets accumulated amortization Finite-Lived Intangible Assets, Accumulated Amortization Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Entity Central Index Key Entity Central Index Key Mass customers Mass Customer [Member] Mass Customer [Member] Entity Emerging Growth Company Entity Emerging Growth Company Selling, general and administrative Selling, General and Administrative Expense Net Amount Derivative Asset, Fair Value, Amount Offset Against Collateral Net Of Derivative Liability, Fair Value, Amount Offset Against Collateral Derivative Asset, Fair Value, Amount Offset Against Collateral Net Of Derivative Liability, Fair Value, Amount Offset Against Collateral Senior Notes Senior Notes [Member] Amortization of unearned equity compensation Share-based Payment Arrangement, Noncash Expense Current portion of operating lease liabilities Current portion of operating lease liabilities Operating Lease, Liability, Current Reconciliation of NRG's basic and diluted earnings per share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Net proceeds from Revolving Credit Facility Proceeds from Lines of Credit Changes in other working capital Changes in other working capital Increase (Decrease) in Other Operating Assets and Liabilities, Net Accounting for Derivative Instruments and Hedging Activities Derivative Instruments and Hedging Activities Disclosure [Text Block] Long-term debt Total long-term debt Long-term Debt, Excluding Current Maturities Derivative [Table] Derivative [Table] Realized gains Debt Securities, Available-for-sale, Realized Gain Assets Assets, Fair Value Disclosure [Abstract] Cash (used)/provided by continuing operations Net Cash Provided by (Used in) Investing Activities, Continuing Operations Total derivative liabilities valued with prices provided by models and other valuation techniques (as a percent) Derivative Liability, Fair Value Determined Using Valuation Techniques, Percentage Derivative Liability, Fair Value Determined Using Valuation Techniques, Percentage Credit Facility [Domain] Credit Facility [Domain] Senior Notes, due 2027 Senior Notes due 2027 [Member] Senior Notes due 2027 [Member] Level 2 Fair Value, Inputs, Level 2 [Member] Income Taxes Income Tax Disclosure [Text Block] Disposal Group Name [Domain] Disposal Group Name [Domain] Unbilled revenues (included within Accounts receivable, net - Contracts with customers) Unbilled Contracts Receivable Pre-tax effects of economic hedges that have not been designated as cash flow hedges, ineffectiveness on cash flow hedges and trading activity on the Company's statement of operations Derivatives Not Designated as Hedging Instruments [Table Text Block] Net Assets Less Noncontrolling Interest Net Assets Less Noncontrolling Interest Net Assets Less Noncontrolling Interest Sierra Club Et Al V. Midwest Generation LLC Sierra Club Et Al V. Midwest Generation LLC [Member] Sierra Club Et Al V. Midwest Generation LLC [Member] Facility fees Line of Credit Facility, Commitment Fee Percentage Net counterparty credit exposure by industry sector and by counterparty credit quality Schedule of Net Exposure to Counter Party Credit Exposure [Table Text Block] Disclosure of the net exposure to counterparty credit risk by category. Schedule of Guarantor Subsidiaries Schedule of Guarantor Subsidiaries [Table Text Block] Schedule of Guarantor Subsidiaries [Table] Unconditional Purchase Obligation, Category of Goods or Services Acquired [Domain] Unconditional Purchase Obligation, Category of Goods or Services Acquired [Domain] Equivalent Shares In Lieu Of Tax Withholding on Equity Compensation Issuances Equivalent Shares In Lieu Of Tax Withholding on Equity Compensation Issuances [Member] Equivalent Shares In Lieu Of Tax Withholding on Equity Compensation Issuances Summary of proceeds from sales of available-for-sale securities and the related realized gains and losses Schedule of Realized Gain (Loss) [Table Text Block] Capital Allocation Plan [Domain] Capital Allocation Plan [Domain] Explains details pertaining to the different capital allocation plans. LIABILITIES AND STOCKHOLDERS' EQUITY Liabilities and Equity [Abstract] Gladstone Gladstone Power Station [Member] Represents the information pertaining to Gladstone Power Station. Senior Secured First Lien Notes Senior Secured First Lien Notes [Member] Senior Secured First Lien Notes [Member] Shares issued under LTIPs (in shares) Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture Transfers into Level 3 Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Transfers into Level 3 Other non-current assets Other non-current assets Other Assets, Noncurrent FTRs Financial Transmission Rights [Member] Financial Transmission Rights [Member] Purchases Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Purchases Cash Flows from Financing Activities Net Cash Provided by (Used in) Financing Activities [Abstract] Other comprehensive income/(loss) Other Comprehensive Income (Loss), Net of Tax Debt Securities Debt Securities [Member] Derivative Contract [Domain] Derivative Contract [Domain] Company's exposure before collateral is expected to roll off by the end of 2019 (as a percent) Counterparty Credit Risk Exposure Percentage Of Credit Risk Roll Off The percentage of net counterparty credit exposure that rolls-off by the end of 2012. Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Long-term debt, including current portion Debt amount Long-term debt Long-term Debt Deferred revenue from contract with customers Contract with Customer, Liability, Increase For Cash Payments Received Contract with Customer, Liability, Increase For Cash Payments Received Loss on debt extinguishment, net Loss on debt extinguishment, net Gains Losses on Extinguishment of Debt, Non Cash Portion Gains Losses on Extinguishment of Debt, Non-cash Portion Segment Reporting Segment Reporting, Policy [Policy Text Block] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Capital expenditures Payments to Acquire Property, Plant, and Equipment Fair Value, Concentration of Risk [Table] Fair Value, Concentration of Risk [Table] Employee Stock Purchase Plan, maximum percentage of eligible compensation Employee Stock Purchase Plan, Maximum Percentage of Compensation Eligible This element represents the maximum percentage of eligible compensation, which can be withheld by employees to purchase shares of the entity. Property, plant and equipment, net Public Utilities, Property, Plant and Equipment, Net Contract Asset and Liabilities Contract with Customer, Asset and Liability [Table Text Block] Recoveries collected Accounts Receivable, Allowance for Credit Loss, Recovery Other Other Debt [Member] Represents other debt instruments not separately accounted disclosed. Utilities, energy merchants, marketers and other Utilities Energy Merchants Marketers And Other [Member] Represents the information pertaining to utilities, energy, merchants, marketers and other. Provision for credit losses Accounts Receivable, Credit Loss Expense (Reversal) Subsequent Event [Table] Subsequent Event [Table] Accounting Policies [Abstract] Accounting Policies [Abstract] Ivampah Master Holdings LLC Ivampah Master Holdings LLC [Member] Ivampah Master Holdings LLC [Member] Additional Paid-In Capital Additional Paid-in Capital [Member] Revenue Recognition Revenue from Contract with Customer [Text Block] Derivative, nonmonetary notional amount, energy (in MMBtu and MWh) Derivative, Nonmonetary Notional Amount, Energy Measure Changes in collateral deposits in support of energy risk management activities Changes in Collateral Deposits Supporting Energy Risk Management Activities Changes in cash collateral deposits for contracts supporting energy risk management activities. Contributions to discontinued operations Contributions to discontinued operations Net (Contributions) To Distributions From Discontinued Operations Net (Contributions) To Distributions From Discontinued Operations Disposal Group Name [Axis] Disposal Group Name [Axis] Receivable [Domain] Receivable [Domain] Realized losses Debt Securities, Available-for-sale, Realized Loss Deferred income taxes Deferred Income Tax Liabilities, Net Non-current tax liability for uncertain tax benefits Liability for Uncertainty in Income Taxes, Noncurrent Dividends per common share (in usd per share) Dividends per common share (in usd per share) Common Stock, Dividends, Per Share, Cash Paid Accounts receivable, net - Contracts with customers Customer Contracts [Member] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Payments for acquisitions of businesses Payments for acquisitions of businesses Payments to Acquire Businesses, Net of Cash Acquired Equity contracts Investments, Fair Value Disclosure Interest rate, stated percentage Debt Instrument, Interest Rate, Stated Percentage Agua Caliente Agua Caliente [Member] Agua Caliente [Member] Entity Address, Address Line One Entity Address, Address Line One Cash Collateral (Held) / Posted Derivative, Collateral, Obligation to Return Cash Net Of Derivative, Collateral, Right to Reclaim Cash Derivative, Collateral, Obligation to Return Cash Net Of Derivative, Collateral, Right to Reclaim Cash Notes receivable Financing Receivable, before Allowance for Credit Loss Entity Address, State or Province Entity Address, State or Province Income Statement Location [Axis] Income Statement Location [Axis] Decrease in cost of operations Decrease In Credit Reserve, Decrease In Cost Of Revenue Decrease In Credit Reserve, Decrease In Cost Of Revenue Wholesale counterparty with net exposure Number Of Wholesale Counterparties With Credit Risk Exposure Number Of Wholesale Counterparties With Credit Risk Exposure Funds deposited by counterparties Funds deposited by counterparties Funds Deposited by Counterparties The amount of cash collateral received from hedge counterparties in support of energy risk management activities for which there is an offsetting liability within current liabilities. These amounts are segregated into separate accounts that are not contractually restricted but, based on the entity's intention, are not available for the payment of the entity's general corporate obligations. Depending on market fluctuations and the settlement of the underlying contracts, the entity will refund this collateral to the counterparties pursuant to the terms and conditions of the underlying trades. Operating Segments Operating Segments [Member] Weighted Average Weighted Average [Member] Corporate/Eliminations Eliminations Intersegment Eliminations [Member] Net Cash (Used)/Provided by Investing Activities Net Cash Provided by (Used in) Investing Activities Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Related Party Transaction [Line Items] Related Party Transaction [Line Items] Derivative instruments Derivative Instruments and Hedges, Noncurrent Net notional volume buy/(sell) of NRG's open derivative transactions broken out by commodity Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] Derivative instruments Derivative Liability, Noncurrent Non-Guarantor Subsidiaries Non-Guarantor Subsidiaries [Member] Accounts payable Accounts Payable, Current Derivative, Auction Price Derivative, Auction Price Derivative, Auction Price Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Ownership interest as percentage Jointly Owned Utility Plant, Proportionate Ownership Share Net exposure (as a percent) Credit Derivative, Maximum Net Exposure, Percentage Represents the percentage of net counterparty credit exposure of the entity. Amortization of emissions allowances and energy credits Amortization of Intangibles and Out of Market Contracts The aggregate (income) expense recorded in earnings to allocate the cost of out-of-market contracts and intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash (income) expense, this element is added back to net income when calculating cash provided by (used in) operations using the indirect method. Entity Interactive Data Current Entity Interactive Data Current Net unrealized gains on open positions related to trading activity Derivative Unrealized Gains on Open Positions Related to Trading Activity, Net This element represents the amount recorded in the entity's statement of operations for net unrealized gains (losses) on open positions related to trading activities. Changes in NRG's common shares issued and outstanding Schedule of Common Stock Outstanding Roll Forward [Table Text Block] Common stock, shares issued (in shares) Balance as of beginning of period (in shares) Balance as of end of period (in shares) Common Stock, Shares, Issued Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Common stock, par or value (in usd per share) Common Stock, Par or Stated Value Per Share Total operating costs and expenses Costs and Expenses Concentration of Credit Risk Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] Schedule of Equity Method Investments [Line Items] Investments Accounted for by the Equity Method Schedule of Equity Method Investments [Line Items] Inventory Inventory, Net STP South Texas Project Units 1 And 2 [Member] This element represents the information pertaining to South Texas Project Units 1 and 2, Bay City, TX. Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Dividends [Abstract] Dividends [Abstract] Senior Notes, due 2026 Senior Notes due 2026 [Member] Senior Notes due 2026 [Member] Fair value inputs, sensitivity analysis Fair Value Inputs, Sensitivity Analysis [Table Text Block] Fair Value Inputs, Sensitivity Analysis [Table Text Block] Derivative Instruments Derivative Asset Fair Value Gross Liability Net Of Derivative Liability Fair Value Gross Asset Derivative Asset Fair Value Gross Liability Net Of Derivative Liability Fair Value Gross Asset Derivative assets: Derivative Asset [Abstract] Offsetting of derivatives by counterparty, liabilities Offsetting Liabilities [Table Text Block] Earnings Per Share Earnings Per Share [Text Block] Derivative liabilities: Derivative Liability [Abstract] Uncertain Tax Benefits Income Tax Uncertainties [Abstract] Property, plant and equipment accumulated depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Award Type [Domain] Award Type [Domain] Revenue from related parties Revenue from Related Parties Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Revolving Credit Facility Revolving Credit Facility [Member] Hedging Designation [Axis] Hedging Designation [Axis] Non-investment grade/non-rated External Credit Rating Not Rated [Member] Represents underlying referenced credits or entities, with respect to guarantees, for which ratings are not available. Capital Structure Schedule of Capitalization [Line Items] Cost of operations Cost of Sales [Member] Number of facilities Number of Facilities Number of Facilities Impairment losses Impairment Losses Impairment Losses including other than temporary impairment losses Total derivative assets valued with prices provided by models and other valuation techniques (as a percent) Derivative Asset, Fair Value Determined Using Valuation Techniques, Percentage This element represents the portion of total fair value of all derivative assets, which are valued using various valuation techniques including internal models based on a fundamental analysis of the market and extrapolation of observable market data with similar characteristics. Effective income tax rate Effective Income Tax Rate Reconciliation, Percent Consolidated Entities [Axis] Consolidated Entities [Axis] U.S. government and federal agency obligations US Government-sponsored Enterprises Debt Securities [Member] Debt Securities, Available-for-sale [Table] Debt Securities, Available-for-sale [Table] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Summary of Results of Discontinued Operations Disposal Groups, Including Discontinued Operations [Table Text Block] 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] Total Liabilities Liabilities Senior Notes, due 2029 Senior Notes Due 2029 [Member] Senior Notes Due 2029 [Member] Schedule of Effective Income Tax Rate Reconciliation Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Reclassifications Reclassification, Policy [Policy Text Block] Common stock; $0.01 par value; 500,000,000 shares authorized; 422,979,893 and 421,890,790 shares issued and 245,623,854 and 248,996,189 shares outstanding at March 31, 2020 and December 31, 2019, respectively Common Stock, Value, Issued Development costs Research and Development Expense Fair value within the derivative instrument valuation on the balance sheets Schedule of Derivatives Instruments Statements of Financial Performance and Financial Position, Location [Table Text Block] Redeemable noncontrolling interest in subsidiaries Redeemable Noncontrolling Interest, Equity, Other, Carrying Amount Proceeds from other asset sales Proceeds from Divestiture of Businesses Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Restricted Cash Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block] Impairment losses Asset Impairment Charges Including Equity Method Investments Asset Impairment Charges including other than temporary impairment losses Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Cash provided/(used) by continuing operations Net Cash Provided by (Used in) Financing Activities, Continuing Operations Incremental shares attributable to the issuance of equity compensation (treasury stock method) (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Weighted average number of common shares outstanding — basic (in shares) Weighted average number of common shares outstanding - diluted (in shares) Weighted Average Number of Shares Outstanding, Basic Operating lease right-of-use assets, net Operating Lease, Right-of-Use Asset Volumetric Underlying Derivative Transactions Volumetric Underlying Derivative Transactions [Abstract] Volumetric Underlying Derivative Transactions [Abstract] Equity Components [Axis] Equity Components [Axis] Accounts receivable, net - Derivative instruments Derivatives Derivative [Member] Generation capacity (in MW) Power Generation Capacity, Megawatts The generation capacity of the entity's power generation facilities as of the balance sheet date, expressed in megawatts. Proceeds from sale of assets, net of cash disposed and sale of discontinued operations, net of fees Proceeds from Sale of Other Productive Assets Derivative, non-monetary notional amount (in shares) Derivative, Non-monetary Notional Amount, Other Derivative, Non-monetary Notional Amount, Other Credit Losses Credit Loss, Financial Instrument [Policy Text Block] Total unrealized mark-to-market gains for trading activity Unrealized Gain (Loss) on Derivatives, Mark To Market, Trading Activities Unrealized Gain (Loss) on Derivatives, Mark To Market, Trading Activities Collateral held (cash and letters of credit) against counterparty credit exposure to a portion of the Company's counterparties Collateral Held Cash and Letters of Credit Carrying amount as of the balance sheet date of cash collateral and letters of credit received by the entity on deposit from third parties in support of energy risk management. Underlying Asset Class [Domain] Underlying Asset Class [Domain] Net unrealized gains on open positions related to economic hedges Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net Regulated Operations [Abstract] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Fair Value of Financial Instruments Fair Value Disclosures [Text Block] Schedule Of Contract Assets And Liabilities [Table] Schedule Of Contract Assets And Liabilities [Table] Schedule Of Contract Assets And Liabilities [Table] Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] Counterparty credit exposure to a portion of the Company's counterparties Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure Purchase of and distributions to noncontrolling interests from subsidiaries Purchase of and distributions to noncontrolling interests from subsidiaries Proceeds from (Payments to) Noncontrolling Interests Variable Interest Entities Disclosure [Abstract] Variable Interest Entities Disclosure [Abstract] -- None. No documentation exists for this element. -- Short Short [Member] Carlsbad Energy Holdings LLC Carlsbad Energy Holdings LLC [Member] Carlsbad Energy Holdings LLC [Member] Repayments of long-term debt Repayments of Other Debt Reorganization costs Restructuring Costs Depreciation and amortization Depreciation, Depletion and Amortization Credit Risk Related Contingent Features Credit Risk Related Contingent Features [Abstract] -- None. No documentation exists for this element. -- Changes in deferred income taxes and liability for uncertain tax benefits Increase (Decrease) in Income Taxes Balance at January 1, 2020 Balance at March 31, 2020 Accounts Receivable, Allowance for Credit Loss Variable Rate [Axis] Variable Rate [Axis] Additional commitments related to project Other Commitment Share repurchases Treasury Stock, Value, Acquired, Cost Method Security Exchange Name Security Exchange Name Disposal Group Classification [Domain] Disposal Group Classification [Domain] Estimated counterparty credit risk exposure to certain counterparties Estimated Counterparty Credit Risk Exposure to Certain Counterparties This element represents the estimated amount of the counterparty credit risk exposure. Litigation Case [Axis] Litigation Case [Axis] Equity investments in affiliates Equity Method Investments Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Additional paid-in-capital Additional Paid in Capital, Common Stock Net Cash Provided/(Used) by Operating Activities Net Cash Provided by (Used in) Operating Activities Nuclear trust fund investments: Nuclear Trust Fund Investments [Abstract] Nuclear Trust Fund Investments Equity Component [Domain] Equity Component [Domain] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Document Transition Report Document Transition Report Cash collateral paid in support of energy risk management activities Cash Collateral Posted Derivative, Collateral, Right to Reclaim Cash Less debt issuance costs Debt Issuance Costs, Net Net income available to common shareholders Net Income (Loss) Available to Common Stockholders, Diluted Consolidated Entities [Domain] Consolidated Entities [Domain] Line of Credit Line of Credit [Member] Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations [Member] Offsetting of Derivatives by Counterparty Master Agreement Level and Collateral Received or Paid Offsetting Assets and Liabilities [Line Items] [Line Items] for Offsetting Assets and Liabilities [Table] Other revenue Products And Services, Other [Member] Products And Services, Other [Member] Counterparty Risk by Institution [Domain] Counterparty Risk by Institution [Domain] Represents the counter party risk exposure by institutions involved. Gain from operations of discontinued components Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Accounts Receivable, Allowance for Credit Loss [Roll Forward] Accounts Receivable, Allowance for Credit Loss [Roll Forward] ESPP Employee Stock [Member] Payments for share repurchase activity Payments for share repurchase activity Payments for Repurchase of Preferred Stock and Preference Stock Not Designated as Hedging Instrument Not Designated as Hedging Instrument [Member] Income Statement [Abstract] Income Statement [Abstract] CONDENSED CONSOLIDATING BALANCE SHEETS Condensed Balance Sheet [Table Text Block] Schedule Of Contract Assets And Liabilities [Line Items] Schedule Of Contract Assets And Liabilities [Line Items] [Line Items] for Schedule Of Contract Assets And Liabilities [Table] Unrealized mark-to-market results Unrealized Mark To Market Results [Abstract] -- None. No documentation exists for this element. -- Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Nuclear decommissioning reserve Decommissioning Liability, Noncurrent Derivative assets Derivative Assets Derivative Asset, Fair Value, Gross Asset Interest rate contracts Interest rate contracts Interest Rate Contract [Member]