Proceeds from divestiture of business Proceeds from Divestiture of Businesses CL&P and NSTAR Electric CL&P And NSTAR Electric [Member] CL&P And NSTAR Electric Goodwill, Rounding Goodwill, Rounding Goodwill, Rounding Disposal group, including discontinued operation, equity Disposal Group, Including Discontinued Operation, Equity Disposal Group, Including Discontinued Operation, Equity Debt and Equity Securities, FV-NI [Line Items] Debt and Equity Securities, FV-NI [Line Items] Percentage of costs or benefits borne under capacity-related contracts by United Illuminated Company (as a percentage) Percentage of Costs or Benefits Borne Under Capacity-Related Contracts by United Illuminated Company Percentage of Costs or Benefits Borne Under Capacity-Related Contracts by United Illuminated Company Expected Return on Plan Assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Average AFUDC Rate (in percent) Public Utilities, Allowance for Funds Used During Construction, Rate Schedule of Expected Benefit Payments Schedule of Expected Benefit Payments [Table Text Block] Estimated costs under construction contract Contractual Obligation, Estimated Annual Cost Contractual Obligation, Estimated Annual Cost 2030 Unrecorded Unconditional Purchase Obligation, to be Paid, Year Five Award Timing Predetermined Award Timing Predetermined [Flag] Capacity available under preferred stock provisions Capacity Available Under Preferred Stock Provisions Capacity Available Under Preferred Stock Provisions Entity File Number Entity File Number Capital Surplus, Paid In Additional Paid-in Capital [Member] Other Federal Tax Credits Effective Income Tax Rate Reconciliation, Tax Credit, Amount RECs RECs [Member] Renewable Energy Credits inventory Tabular List, Table Tabular List [Table Text Block] Storm Costs Storm Costs and Expenses Storm Costs and Expenses Power Purchase Agreement Security Power Purchase Guarantee [Member] Power Purchase Guarantee Target Asset Allocation (in percent) Defined Benefit Plan, Plan Assets, Target Allocation, Percentage Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block] Carrying Amounts and Estimated Fair Values of Financial Instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Maximum exposure Guarantor Obligations, Maximum Exposure, Undiscounted Eversource Service Pension and PBOP Plans Eversource Service Pension And PBOP Plans [Member] Eversource Service Pension And PBOP Plans [Member] Goodwill [Line Items] Goodwill [Line Items] Research and Development Tax Credits Effective Income Tax Rate Reconciliation, Tax Credit, Research, Amount Condensed Cash Flow Statement [Table] Condensed Cash Flow Statement [Table] Other Other Expenses Measurement Basis [Axis] Measurement Basis [Axis] Adjustment to Compensation: Adjustment to Compensation [Axis] Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Tax deficiency/(excess stock benefit) Share-Based Payment Tax Deficiency Effective Income Tax Rate Reconciliation, Tax Deficiency/(Excess Stock Benefit), Amount Effective Income Tax Rate Reconciliation, Tax Deficiency/(Excess Stock Benefit), Amount REVENUES Revenue from Contract with Customer [Text Block] REGULATORY ACCOUNTING Public Utilities Disclosure [Text Block] Contract term (in years) Long-Term Purchase Commitment, Period Cash Dividends on Preferred Stock Payments of Ordinary Dividends, Preferred Stock and Preference Stock Stock, Class of Stock [Table] Stock, Class of Stock [Table] Basis point change Loss Contingency, Basis Spread Loss Contingency, Basis Spread Schedule of Components of Other Income, Net Other Income, Net [Table Text Block] [Table Text Block] for Other Income, Net [Table] Supplemental Balance Sheet Information Related to Leases Lessee, Leases, Supplemental Balance Sheet Information [Table Text Block] Lessee, Leases, Supplemental Balance Sheet Information [Table Text Block] Electric Transmission Eversource Electric Transmission [Member] Eversource Electric Transmission [Member] Income tax expense (benefit), state tax, return to provision process Income Tax Expense (Benefit), State Tax, Return To Provision Process Income Tax Expense (Benefit), State Tax, Return To Provision Process Total Current Current Income Tax Expense (Benefit) 2020 Debentures due 2030 3.950% Notes Due 2030 [Member] 3.950% Notes Due 2030 Loss on Offshore Wind Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Amount Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Amount Employee Benefits Deferred Tax Liabilities, Employee Benefits Deferred Tax Liabilities, Employee Benefits Adjustment to Compensation, Amount Adjustment to Compensation Amount Pension and SERP Pension Plan Pension Plan [Member] Yankee Gas Series Z First Mortgage Bonds Yankee Gas Series Z First Mortgage Bonds [Member] Yankee Gas Series Z First Mortgage Bonds South Fork Wind, LLC South Fork Wind LLC [Member] South Fork Wind LLC Percentage of ROE for any incentive project Loss Contingency, Percentage of ROE for Any Incentive Project Loss Contingency, Percentage of ROE for Any Incentive Project Employee Stock Option Share-Based Payment Arrangement, Option [Member] Type Of Inventory By Major Asset Class [Axis] Type Of Inventory By Major Asset Class [Axis] Type of inventory by major asset class Reserve balances related to former MGP sites Accrual for Environmental Loss Contingencies, Component Amount Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Cash Cash and Cash Equivalents, Policy [Policy Text Block] Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] Effective Income Tax Rate Reconciliation, Percent [Abstract] Effective Income Tax Rate Reconciliation, Percent [Abstract] Ultimate rate Defined Benefit Plan, Ultimate Health Care Cost Trend Rate Impairment charge Asset Impairment Charges Common Shareholders' Equity Beginning balance Ending balance Common Stockholder's Equity Equity, Attributable to Parent Schedule of Available-for-sale Securities [Table] Debt Securities, Available-for-Sale [Table] Other Comprehensive Income, Net of Tax: Other Comprehensive Income/(Loss), Net of Tax: Other Comprehensive Income, Net of Tax: Other Comprehensive Income (Loss), Net of Tax [Abstract] Insider Trading Policies and Procedures [Line Items] Authorized (in shares) Common Stock, Shares Authorized Surety Bonds Surety Bond [Member] Short-term borrowing limit approved by regulatory agency Short-Term Borrowing Limit Approved By Regulatory Agency Short-Term Borrowing Limit Approved By Regulatory Agency Uncollectible Costs Deferred Accounts Receivable, Allowance For Credit Loss , Deferred Expense (Reversal) Accounts Receivable, Allowance For Credit Loss , Deferred Expense (Reversal) Issuance of Common Shares (in shares) Stock Issued During Period, Shares, New Issues Noncontrolling Interest [Line Items] Noncontrolling Interest [Line Items] LIABILITIES AND CAPITALIZATION LIABILITIES AND CAPITALIZATION Liabilities and Equity [Abstract] State and Local Jurisdiction State and Local Jurisdiction [Member] Cover [Abstract] Cover [Abstract] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] ASSETS HELD FOR SALE Disposal Groups, Including Discontinued Operations, Disclosure [Text Block] Maximum Maximum [Member] Net Income Attributable to Noncontrolling Interests Net Income Attributable to Noncontrolling Interests Net Income (Loss) Attributable to Noncontrolling Interest Prepaid Pension and PBOP Prepaid Pension and PBOP Pension And Other Postretirement Defined Benefit Plans Assets Noncurrent Pension And Other Postretirement Defined Benefit Plans Assets Noncurrent Compensation/Progression Rate Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase Greater than ten years Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 10 Income Tax Contingency [Line Items] Income Tax Contingency [Line Items] Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Debt Instrument [Line Items] Debt Instrument [Line Items] Total Other Long-Term Debt Total Other Long-Term Debt [Member] Retail (Non-Hardship), Wholesale, and Other Retail Non Hardship Wholesaleand Other Receivables [Member] Retail Non Hardship Wholesaleand Other Receivables Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Unusual or Infrequent Item, or Both [Domain] Unusual or Infrequent Item, or Both [Domain] Period of payment to generation facility owner Unrecorded Unconditional Purchase Obligation, Period of Payment to Generation Facility Owner Unrecorded Unconditional Purchase Obligation, Period of Payment to Generation Facility Owner Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Schedule of Supplemental Cash Flow [Line Items] Schedule of Supplemental Cash Flow [Line Items] [Line Items] for Schedule of Supplemental Cash Flow [Table] Electric Distribution Eversource Electric Distribution [Member] Eversource Electric Distribution [Member] Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] Total Long-Term Liabilities Held for Sale Disposal Group, Including Discontinued Operation, Liabilities, Noncurrent Total pre-tax amount Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Entity Shell Company Entity Shell Company NSTAR Electric Debentures 3.25% NSTAR Electric Debentures 3.25% [Member] NSTAR Electric Debentures 3.25% Environmental Remediation Site [Domain] Environmental Remediation Site [Domain] Distribution revenue Distribution Revenue Distribution Revenue Schedule of Long-term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Issuance Proceeds from Issuance of Debt Regulatory Assets [Line Items] Regulatory Asset [Line Items] Orsted Orsted [Member] Orsted Actuarial Loss/(Gain) Reclassified from Held for Sale Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassified From Held for Sale Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassified From Held for Sale Proceeds from sale, land, held-for-investment Proceeds from Sale, Land, Held-for-Investment Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Common Shareholders' Equity: Statement of Stockholders' Equity [Abstract] Operating Segments Operating Segments [Member] Estimate of possible loss for each 10 basis point change to base ROE Estimate of possible loss for each 10 basis point change to base ROE Estimate of possible loss for each 10 basis point change to base ROE Schedule of Supplemental Cash Flow Information Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Annual purchase requirement (in MWh) Long-Term Purchase Commitment, Minimum Energy Volume Required Schedule of Utility Inventory Schedule of Utility Inventory [Table Text Block] Historical average term of capital additions (in years) Public Utilities, Historical Average Of Capital Additions, Term Public Utilities, Historical Average Of Capital Additions, Term Comprehensive Income Attributable to Noncontrolling Interests Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Line of Credit Facility [Table] Line of Credit Facility [Table] Prior Service Cost Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, Prior Service Cost (Credit), before Tax Reclassification out of Accumulated Other Comprehensive Income [Table] Reclassification out of Accumulated Other Comprehensive Income [Table] Letter of Credit Letter of Credit [Member] Regulated Operation, Regulatory Liability [Table] Regulated Operation, Regulatory Liability [Table] Income/(Loss) Before Income Tax Expense Income/(Loss) Before Income Tax Benefit Income (Loss) from Continuing Operations before Income Taxes, Domestic Current Portion Operating Lease, Liability, Current Eversource Parent and Other Companies excluding NSTAR Electric Eversource Parent and Other Companies excluding NSTAR Electric [Member] Eversource Parent and Other Companies excluding NSTAR Electric Supplemental Non-Cash Information on Lease Liabilities: Lessee, Lease, Supplemental Non-Cash Information [Abstract] Lessee, Lease, Supplemental Non-Cash Information [Abstract] Interest on Lease Liabilities Finance Lease, Interest Expense Borrowed Funds Allowance for Funds Used During Construction, Capitalized Interest Equity method investment, remaining purchase price paid Equity Method Investment, Remaining Purchase Price Paid Equity Method Investment, Remaining Purchase Price Paid Document Fiscal Period Focus Document Fiscal Period Focus Compensation/Progression Rate (in percent) Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase 2020 Series U due 2050 2.400% Series U Due 2050 [Member] 2.400% Series U Due 2050 Allowance for Uncollectible Accounts Receivable [Policy Text Block] Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Award Timing Method Award Timing Method [Text Block] Litigation Case [Domain] Litigation Case [Domain] Return of Capital from Subsidiaries Proceeds from Divestiture of Businesses and Interests in Affiliates Award Type [Axis] Award Type [Axis] Eversource Eversource Parent Commercial Paper Program Parent Company [Member] Solar Generation Assets Average Useful Life Generation Assets Average Useful Life Revolution Wind Revolution Wind [Member] Revolution Wind Evironmental Sites with Best Estimate Evironmental Sites with Best Estimate [Member] Evironmental Sites with Best Estimate [Member] NSTAR Gas Series Y First Mortgage Bonds NSTAR Gas Series Y First Mortgage Bonds [Member] NSTAR Gas Series Y First Mortgage Bonds Investment, Name [Domain] Investment, Name [Domain] Asset Retirement Obligations Asset Retirement Obligations [Member] Asset Retirement Obligations [Member] Trading Symbol Trading Symbol 2029 Lessee, Operating Lease, Liability, to be Paid, Year Four Income tax expense (benefit) from contingent liability increase (decrease) Income Tax Expense (Benefit) From Contingent Liability Increase (Decrease) Income Tax Expense (Benefit) From Contingent Liability Increase (Decrease) Maximum percentage cap of ROE for incentive projects Loss Contingency, Maximum Percentage Of ROE For Incentive Projects Loss Contingency, Maximum Percentage Of ROE For Incentive Projects Operating Loss Carryforwards [Table] Operating Loss Carryforwards [Table] Changes in Valuation Allowances Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent Special Deposits Deposits Assets, Current Entity Address, City or Town Entity Address, City or Town Short-term Debt, Type [Domain] Short-Term Debt, Type [Domain] Property, Plant and Equipment, Gross Public Utilities, Property, Plant and Equipment, Plant in Service Finance Leases Finance Lease, Weighted Average Discount Rate, Percent CL&P, NSTAR Electric and PSNH CL&P, NSTAR Electric and PSNH [Member] CL&P, NSTAR Electric and PSNH [Member] Net Deferred Tax Assets Deferred Tax Assets, Net of Valuation Allowance Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount (Decrease)/Increase in Notes Payable Increase (Decrease) in Notes Payable To Eversource Parent Proceeds from (Repayments of) Short-Term Debt Restricted Stock Units (RSUs) Restricted Stock Units (RSUs) [Member] Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Water Reclassified as Assets Held for Sale Defined Benefit Plan, Reclassification to Assets Held for Sale, Pension Plan Assets Defined Benefit Plan, Reclassification to Assets Held for Sale, Pension Plan Assets Distribution - Electric Distribution Assets Average Useful Life Distribution Assets Average Useful Life K-Bar Adjustment K-Bar Adjustment [Member] K-Bar Adjustment Losses on Offshore Wind Loss on Offshore Wind Equity Method Investment, Other-than-Temporary Impairment Entity Emerging Growth Company Entity Emerging Growth Company 2028 Long-Term Debt, Maturity, Year Three Finance Leases Finance Lease, Weighted Average Remaining Lease Term SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT Condensed Financial Information of Parent Company Only Disclosure [Text Block] Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year [Member] Revenues from Contracts with Customers Revenue from Contract with Customer, Including Assessed Tax Unamortized Debt Issuance Costs Debt Issuance Costs, Net Restricted cash Restricted Cash Restricted Cash and Cash Equivalent 2026 Defined Benefit Plan, Expected Future Benefit Payment, Year One Less amount representing interest Finance Lease, Liability, Undiscounted Excess Amount Beginning balance (in shares) Ending balance (in shares) Common stock outstanding (in shares) Common Stock, Shares, Outstanding Series F of 1955 Preferred Stock at $2.09 Series F of 1955 Preferred Stock at $2.09 [Member] Series F of 1955 Preferred Stock at $2.09 [Member] Uncollectible Expense Uncollectible Expense Accounts Receivable, Credit Loss Expense (Reversal) Allowance for Doubtful Accounts SEC Schedule, 12-09, Allowance, Credit Loss [Member] OCI Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment and Tax [Abstract] 2030 Recorded Unconditional Purchase Obligation, to be Paid, Year Five Schedule of Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] Internal Revenue Service (IRS) Internal Revenue Service (IRS) [Member] CYAPC and YAEC CYAPC and YAEC CYAPC and YAEC [Member] Series of 1963 Preferred Stock at 4.5% Series of 1963 Preferred Stock at 4.5% [Member] Series of 1963 Preferred Stock at 4.5% [Member] Percentage of costs and benefits borne Percentage of Costs and Benefits Borne Under Unrecorded Unconditional Purchase Obligation Percentage of Costs and Benefits Borne Under Unrecorded Unconditional Purchase Obligation Change in valuation allowance Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year [Member] Fair value of guarantees Guarantor Obligations, Current Carrying Value Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative Instruments and Hedging Activities Disclosure [Abstract] Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Restatement Determination Date Restatement Determination Date Income Tax Expense Income Tax Expense Tax Effect Income Tax (Expense)/Benefit Income tax expense (benefit) Income Tax Expense (Benefit) Commercial operation, term Commercial Operation, Term Commercial Operation, Term Percentage of base ROE of complaint period Percentage of Base ROE of Complaint Period Percentage of Base ROE of Complaint Period Total capitalization (as a percentage) Percentage of Total Capitalization Percentage of Total Capitalization Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Pending purchase Defined Benefit Plan, Plan Assets, Pending Purchase Defined Benefit Plan, Plan Assets, Pending Purchase Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Qualified Cash Flow Hedging Instruments Qualified Cash Flow Hedging Instruments Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax Long-term Purchase Commitment [Table] Long-Term Purchase Commitment [Table] Beginning balance (in dollars per share) Ending balance (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested and Vested Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested and Vested Weighted Average Grant Date Fair Value Total Recorded Unconditional Purchase Obligation Discontinued Operations and Disposal Groups [Abstract] Condensed Cash Flow Statements, Captions [Line Items] Condensed Cash Flow Statements, Captions [Line Items] Unbilled Revenues Disposal Group, Including Discontinued Operation, Accounts, Unbilled Revenues Disposal Group, Including Discontinued Operation, Accounts, Unbilled Revenues Funding and Indemnification Obligations Indemnification Agreement [Member] Guarantor Obligation [Table] Guarantor Obligation [Table] Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] Sale of Water Unregulated Business and Water Acquisition, net Goodwill, Acquired During Period Federal Income Taxes Income Tax Paid, Federal, after Refund Received All Trading Arrangements All Trading Arrangements [Member] Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Current and Long-Term Derivative Assets Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract] Other, Net Effective Income Tax Rate Reconciliation, Other Adjustments, Amount Deferred Tax Liabilities: Deferred Tax Liabilities, Gross [Abstract] Shares outstanding (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number Rate increase (decrease) requested Public Utilities, Requested Rate Increase (Decrease), Amount Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Schedule of Restrictions on Retained Earnings [Line Items] Schedule of Restrictions on Retained Earnings [Line Items] [Line Items] for Schedule of Restrictions on Retained Earnings [Table] Net Cash Flows Provided by Operating Activities Net Cash Flows Provided by Operating Activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation (Decrease)/Increase in Notes Payable Repayments of Short-Term Debt Debt instrument term (in years) Debt Instrument, Term Equity Method Investments and Joint Ventures [Abstract] Equity Method Investments and Joint Ventures [Abstract] Aquarion Water Company Aquarion Water Company [Member] Aquarion Water Company [Member] Preferred stock, par value (in dollars per share) Preferred Stock, Par or Stated Value Per Share Estimated useful life of property, plant and equipment (in years) Property, Plant and Equipment, Useful Life Subsequent Event Subsequent Event [Member] Schedule of Equity Method Investments [Line Items] Schedule of Equity Method Investments [Line Items] Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] PEO Total Compensation Amount PEO Total Compensation Amount Settlement Loss Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), before Tax Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] Depreciation Depreciation 2014 Series A due 2044   Series A 2014 Notes Due 2044 [Member] Series A 2014 Notes Due 2044 [Member] Tax Equity Investment in South Fork Wind Offshore Wind Business [Member] Offshore Wind Business 2029 Finance Lease, Liability, to be Paid, Year Four Commodity Supply and Price Risk Management Derivative Liability, Subject to Master Netting Arrangement, before Offset Equity Components [Axis] Equity Components [Axis] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Schedule Of Rate Reduction Bonds, Principal And Interest Payments Schedule Of Rate Reduction Bonds, Principal And Interest Payments [Table Text Block] Schedule Of Rate Reduction Bonds, Principal And Interest Payments Current Portion Classified as Long-Term Debt Long-Term Debt, Current Maturities Classified As Noncurrent Long-Term Debt, Current Maturities Classified As Noncurrent Tax Equity Capital Contribution Agreement Tax Equity Capital Contribution Agreement [Member] Tax Equity Capital Contribution Agreement Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Number of reportable segments Number of Reportable Segments EMPLOYEE BENEFITS Compensation and Employee Benefit Plans [Text Block] Unamortized Premiums and Discounts, Net   Debt Instrument, Unamortized Discount (Premium), Net Transmission - Electric Transmission Assets Average Useful Life Transmission Assets Average Useful Life New general obligation bonds to fund the electric vehicle charging program (percentage) New General Obligation Bonds to Fund the Electric Vehicle Charging Program, percentage New General Obligation Bonds to Fund the Electric Vehicle Charging Program, percentage Regulatory Tracking Mechanisms Regulatory Tracker Deferrals Regulatory Assets [Member] Regulatory tracker deferrals are approved rate mechanisms that allow utilities to recover costs in specific business segments through reconcilable tracking mechanisms that are reviewed at least annually by the applicable regulatory commission. Regulatory tracker deferrals are recorded as regulatory assets if unrecovered costs are in excess of collections and are recorded as regulatory liabilities if collections are in excess of costs. Issuance of Treasury Shares Stock Issued During Period, Value, Treasury Stock Reissued 2007 Senior Notes Series D due 2037 Series D Notes Due 2037 [Member] Series D Notes Due 2037 [Member] Public Utilities, Inventory [Line Items] Public Utilities, Inventory [Line Items] Regulatory Liabilities Total Long-Term Regulatory Liabilities Regulatory Liability, Noncurrent Entity Address, State or Province Entity Address, State or Province Financing Cash Flows from Finance Leases Finance Lease, Principal Payments Total Long-Term Assets Held for Sale Disposal Group, Including Discontinued Operation, Assets, Noncurrent Period of maturity restricting provisions of debt Period of Maturity Restricting Provisions of Debt Period of Maturity Restricting Provisions of Debt Dividends on Common Stock Dividends, Common Stock 2029 Defined Benefit Plan, Expected Future Benefit Payment, Year Four Total Current Liabilities Liabilities, Current Long-term Purchase Commitment, Category of Item Purchased [Domain] Long-Term Purchase Commitment, Category of Item Purchased [Domain] Individual: Individual [Axis] Environmental Remediation Costs Environmental Remediation Costs [Member] Environmental Remediation Costs Defined contribution plan, cost recognized Defined Contribution Plan, Cost 2029 Recorded Unconditional Purchase Obligation, to be Paid, Year Four Thereafter Rate Reduction Bonds, Principal And Interest Payments To Be Paid, After Year Five Rate Reduction Bonds, Principal And Interest Payments To Be Paid, After Year Five Yankee Gas Series Y First Mortgage Bonds Yankee Gas Series Y First Mortgage Bonds [Member] Yankee Gas Series Y First Mortgage Bonds Income Tax Jurisdiction [Domain] Income Tax Jurisdiction [Domain] Public utilities, approved return on equity, percentage Public Utilities, Approved Return on Equity, Percentage Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities Right-of-Use Asset Obtained in Exchange for Finance Lease Liability Cash Dividends on Common Shares Cash Dividends on Common Shares Payments of Ordinary Dividends, Common Stock Document Annual Report Document Annual Report Entities [Table] Entities [Table] Amortization Amortization Period of accounts receivable recoverable under financial or medical duress Period of Accounts Receivable Recoverable Under Financial or Medical Duress Period of Accounts Receivable Recoverable Under Financial or Medical Duress Goodwill Impairment Loss Statement Of Income Or Comprehensive Income Extensible Enumeration Not Disclosed Flag Goodwill Impairment Loss Statement Of Income Or Comprehensive Income Extensible Enumeration Not Disclosed Flag Goodwill Impairment Loss Statement Of Income Or Comprehensive Income Extensible Enumeration Not Disclosed Flag Summary of Accounting Policies [Table] Summary of Accounting Policies [Table] Summary of Accounting Policies [Table] Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Base ROE percentage challenged by complainants Loss Contingency, Base ROE Percentage Challenged by Complainants Loss Contingency, Percentage of Base ROE Challenged by Complainants Retirement of Long-Term Debt Repayments of Long-Term Debt Entity Interactive Data Current Entity Interactive Data Current Number of regulated utilities Number of Regulated Utilities Number of Regulated Utilities Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Condensed Income Statement [Table] Condensed Income Statement [Table] Funded Status as of December 31st Defined Benefit Plan, Funded (Unfunded) Status of Plan Offshore wind construction-related purchase agreements with third-party contractors Purchase Guarantee [Member] Purchase Guarantee Property Tax Accruals Deferred Tax Liabilities Resulting From Property Tax Accruals And Other Schedule of Compensation Expense and Income Tax Benefit Disclosure of Share-Based Compensation Arrangements by Share-Based Payment Award [Table Text Block] Deferred Pre-Staging And Storm Restoration Costs Deferred Pre-Staging And Storm Restoration Costs [Member] Deferred Pre-Staging And Storm Restoration Costs Schedule of Estimated Future Annual Costs of Long term Contractual Agreement Long-Term Purchase Commitment [Table Text Block] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Net Operating Loss Carryforwards Deferred Tax Assets, Operating Loss Carryforwards Capital Contributions from Eversource Parent Proceeds from Contributions from Parent South Fork Wind And Revolution Wind South Fork Wind And Revolution Wind [Member] South Fork Wind And Revolution Wind Property, Plant and Equipment, Type [Axis] Long-Lived Tangible Asset [Axis] NSTAR Gas Series Z First Mortgage Bonds NSTAR Gas Series Z First Mortgage Bonds [Member] NSTAR Gas Series Z First Mortgage Bonds Non-GSEP Plant Non-GSEP Plant [Member] Non-GSEP Plant MGP Site accrual MGP Site accrual [Member] Portion of environmental liability associated with MGP sites Marketable Securities Marketable Securities, Noncurrent 2027 Finance Lease, Liability, to be Paid, Year Two Deferred Storm Restoration Costs Deferred Storm Restoration Costs [Member] Deferred Storm Restoration Costs [Member] Balance at beginning of period Balance at end of period SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount Other Other Equity Method Investments [Member] Other Equity Method Investments [Member] Auditor [Table] Auditor [Table] Audit Information [Abstract] Audit Information [Abstract] 2027 Defined Benefit Plan, Expected Future Benefit Payment, Year Two Other Long-Term Assets Other Long-Term Assets Other Assets, Noncurrent Accrued Interest Interest Payable, Current Entity Central Index Key Entity Central Index Key PEO Name PEO Name Balance as of Beginning of Year Balance as of End of Year Asset retirement obligations Asset Retirement Obligation Schedule of Maturities of Long-Term Debt Outstanding Schedule of Maturities of Long-Term Debt [Table Text Block] Operating Revenues Operating Revenues Other revenues Revenues Revenues Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year [Member] UI UI [Member] UI [Member] Regulatory Liabilities [Line Items] Regulatory Liability [Line Items] Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Share-Based Compensation Awards and Other (in shares) Incremental Common Shares Attributable To Dilutive Effect Of Share-Based Payment Arrangements And Other Incremental Common Shares Attributable To Dilutive Effect Of Share-Based Payment Arrangements And Other Fair Value as of Beginning of Year Fair Value as of End of Year Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value Defined Benefit Plan [Table] Defined Benefit Plan [Table] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Materials, Supplies, Natural Gas and REC Inventory Materials, Supplies and REC Inventory Inventory, Raw Materials and Supplies, Gross Schedule of Derivative Instruments in Statement of Financial Position, Fair Value Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] NECEC Transmission Service Agreement NECEC Transmission Service Agreement [Member] NECEC Transmission Service Agreement Exercise Price Award Exercise Price Long-term Contract for Purchase of Electric Power [Domain] Long-Term Contract for Purchase of Electric Power [Domain] Entity Filer Category Entity Filer Category Class of Stock [Domain] Class of Stock [Domain] Eversource Parent Company and Nstar Electric Company Eversource Parent Company and Nstar Electric Company [Member] Eversource Parent Company and Nstar Electric Company Capitalization: Capitalization, Long-Term Debt and Equity [Abstract] Benefits Paid Defined Benefit Plan, Benefit Obligation, Benefits Paid DIVIDEND RESTRICTIONS Dividend Payment Restrictions [Text Block] U.S. Federal Statutory Income Tax Expense at 21% Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Subsequent Event Type [Axis] Subsequent Event Type [Axis] Contingent liability Business Combination, Contingent Consideration, Liability, Current Equity Method Wind Investments Deferred Tax Assets, Equity Method Investments Regulated Operation, Inventory [Table] Regulated Operation, Inventory [Table] Other Other Assets Average Useful Life Other Assets Average Useful Life Long-Term Debt Long-term debt Long-Term Debt, Excluding Current Maturities Employee Employees [Member] Employees [Member] Nonrelated Party Nonrelated Party [Member] Tax Equity Investment in South Fork Wind South Fork Wind Holdings, LLC Class A shares [Member] South Fork Wind Holdings, LLC Class A shares Statement of Financial Position Location, Balance [Axis] Statement of Financial Position Location, Balance [Axis] Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year [Member] Entity Address, Address Line One Entity Address, Address Line One Entity Address, Address Line Two Entity Address, Address Line Two Deferred Debits and Other Assets: Long-Term Investments [Abstract] Accumulated Other Comprehensive Income (Loss) Total AOCI Attributable to Parent [Member] Allowance for uncollectible accounts, current Accounts Receivable, Allowance for Credit Loss, Current Base Rate Adjustment Base Rate Adjustment [Member] Base Rate Adjustment Recovery period (in years) Regulatory Asset, Amortization Period Amount of regulatory costs not yet approved Amount of Regulatory Costs Not yet Approved DERIVATIVE INSTRUMENTS Derivative Instruments and Hedging Activities Disclosure [Text Block] Prior Service Cost/(Credit) Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Purchased Power, Purchased Natural Gas and Transmission, Other Taxes and Energy Efficiency Utilities Operating Expense, Other PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION Preferred Stock [Text Block] Common Shares Authorized and Issued Schedule of Preferred Stock Not Subject to Mandatory Redemption Schedule of Stock by Class [Table Text Block] 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] Deferred costs Deferred Regulatory Costs Deferred Regulatory Costs Fair Value as of Grant Date Award Grant Date Fair Value Derivative Assets Deferred Tax Liabilities Regulatory Assets Derivative Assets Other Revenues from Contracts with Customers Other Revenue Adjustments from Contracts with Customers [Member] Other Revenue Adjustments from Contracts with Customers [Member] Public utilities, approved rate, annual cap on cost recovery Public Utilities, Approved Rate, Annual Cap On Cost Recovery Public Utilities, Approved Rate, Annual Cap On Cost Recovery United States Defined Benefit Plan, Equity Securities, US [Member] Disposal Group, Held-for-Sale, Not Discontinued Operations Disposal Group, Held-for-Sale, Not Discontinued Operations [Member] Net Operating Loss Operating Loss Carryforwards Employee Benefits Employee Benefits and Share-Based Compensation Schedule of Issuance and Repayments of Long-Term Debt Schedule of Long-Term Debt Instruments [Table Text Block] Derivative Instruments and Hedging Activities Disclosures [Table] Derivative Instruments and Hedging Activities Disclosures [Table] Pre-65 Plan Pre-65 Plan [Member] Pre-65 Plan [Member] Granted (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period Title and Position [Domain] Title and Position [Domain] Tropical Storm Isaias Tropical Storm Isaias [Member] Tropical Storm Isaias Percentage of costs and benefits borne by United Illuminated Company Percentage of Costs and Benefits Borne Under Unrecorded Unconditional Purchase Obligation by United Illuminated Company Percentage of Costs and Benefits Borne Under Unrecorded Unconditional Purchase Obligation by United Illuminated Company Forfeited (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeited in Period Total unrecognized compensation expense Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Counterparty Name [Domain] Counterparty Name [Domain] 2027 Lessee, Operating Lease, Liability, to be Paid, Year Two Condensed Financial Information Disclosure [Abstract] Condensed Financial Information Disclosure [Abstract] Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Best estimate of potential remediation costs (up to) Site Contingency, Loss Exposure Not Accrued, Best Estimate SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis] SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis] Series of 1968 Preferred Stock at 6.56% Series of 1968 Preferred Stock at 6.56% [Member] Series of 1968 Preferred Stock at 6.56% [Member] Title Trading Arrangement, Individual Title Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Condensed Statement of Income Captions [Line Items] Condensed Statement of Income Captions [Line Items] 2028 Defined Benefit Plan, Expected Future Benefit Payment, Year Three Other Current Liabilities Disposal Group, Including Discontinued Operation, Other Liabilities, Current Actuarial (Loss)/Gain Reclassified as Net Periodic Benefit (Expense)/Income Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax 2023 Series W due 2053 5.150% Series W Due 2053 [Member] 5.150% Series W Due 2053 2017 Series A due 2027 Series A 2017 Notes Due 2027 [Member] Series A 2017 Notes Due 2027 [Member] Non-PEO NEO Non-PEO NEO [Member] 2019 Series T due 2049   Series T Notes Due 2049 [Member] Series T Notes Due 2049 [Member] 2021 Debentures due 2031 1.950% Notes Due 2031 [Member] 1.950% Notes Due 2031 Preferred stock, dividend rate (as a percentage) Preferred Stock, Dividend Rate, Percentage Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] 2006 Series A due 2036 Series A 2006 Notes Due 2036 [Member] Series A 2006 Notes Due 2036 [Member] Pre-Tax Unrealized Gains Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax Schedule of Components of Regulatory Liabilities Schedule of Regulatory Liabilities [Table Text Block] Amortization of Prior Service Cost Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member] Award Type [Domain] Award Type [Domain] 2026 Lessee, Operating Lease, Liability, to be Paid, Year One GOODWILL Goodwill Disclosure [Text Block] Equity Awards Adjustments Equity Awards Adjustments [Member] Other Other Noncash Income (Expense) Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Receivables and Unbilled Revenues, Net Receivables and Unbilled Revenues, Net Increase (Decrease) in Accounts and Other Receivables Compensation Amount Outstanding Recovery Compensation Amount Thereafter Unrecorded Unconditional Purchase Obligation, to be Paid, after Year Five Income tax expense (benefit), tax credits, return to provision process Income Tax Expense (Benefit), Tax Credits, Return To Provision Process Income Tax Expense (Benefit), Tax Credits, Return To Provision Process Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Fair Value Estimate of Fair Value Measurement [Member] NSTAR Gas - First Mortgage Bonds due 2029 - 2051 Unsecured Notes Due 2029-2051 [Member] Unsecured Notes Due 2025-2051 [Member] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Additions, Charged to Costs and Expense SEC Schedule, 12-09, Valuation Allowances and Reserves, Additions, Charge to Cost and Expense MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] One to five years Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year One Through Five Net Amount Recorded as a Derivative Derivative Asset, Subject to Master Netting Arrangement, before Offset of Collateral Investment (Loss)/Income Investment Income (Loss) [Member] Investment Income (Loss) [Member] AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] Weighted Average Common Shares Outstanding: Weighted Average Common Shares Outstanding: Weighted Average Number of Shares Outstanding Reconciliation [Abstract] Restricted Cash Disposal Group, Including Discontinued Operation, Restricted Cash Disposal Group, Including Discontinued Operation, Restricted Cash 2023 Series A due 2053 2023 Series A due 2053 [Member] 2023 Series A due 2053 Water Reclassified as Assets Held for Sale Defined Benefit Plan, Reclassification to Assets Held for Sale, Obligation Defined Benefit Plan, Reclassification to Assets Held for Sale, Obligation Schedule of Amounts Recognized in Regulatory Assets and OCI Schedule of Amounts Recognized in Other Comprehensive Income (Loss) [Table Text Block] Documents Incorporated by Reference Documents Incorporated by Reference [Text Block] Pre-1983 Spent Nuclear Fuel Obligation (CYAPC) Spent Nuclear Fuel Obilgation CY [Member] Commercial Commercial [Member] Commercial [Member] Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Six to ten years Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 Offshore Wind Contingent Liability - Long-Term Portion Offshore Wind Contingent Liability - Long-Term Portion Offshore Wind Contingent Liability - Long-Term Portion Global Defined Benefit Plan, Equity Securities, Global [Member] Defined Benefit Plan, Equity Securities, Global [Member] Accumulated Other Comprehensive Income/(Loss) Accumulated Other Comprehensive Income (Loss), Net of Tax Other Information Related to Leases Lessee, Leases, Other Information [Table Text Block] Lessee, Leases, Other Information [Table Text Block] Equity method investment, liability obligations Equity Method Investment, Liability Obligations Equity Method Investment, Liability Obligations Long-term Purchase Commitment [Line Items] Long-Term Purchase Commitment [Line Items] 2026 Long-Term Debt, Maturity, Year One Financial Instruments [Domain] Financial Instruments [Domain] Changes in Unrealized Gains on Marketable Securities Changes in Unrealized Gains on Marketable Securities OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax Percentage of incentive cap on total ROE Loss Contingency, Percentage Of Incentive Cap On Total ROE Loss Contingency, Percentage Of Incentive Cap On Total ROE 2030 Long-Term Debt, Maturity, Year Five Performance Shares Performance Shares [Member] Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Environmental Remediation Site [Axis] Environmental Remediation Site [Axis] Postemployment Benefits [Abstract] Postemployment Benefits [Abstract] Actuarial Loss Regulatory Asset Gains Losses Before Tax The pretax net amount of gains and losses that are not yet recognized as a component of net periodic benefit cost, and that are recognized as increases or decreases in other comprehensive income as they arise. Gains and losses are due to changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan. Environmental site quantity remaining Environmental Site Quantity Remaining Environmental Site Quantity Remaining Minimum Minimum [Member] Measurement Period Adjustment Goodwill, Measurement Period Adjustment Accounts, Notes, Loans and Financing Receivable [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Company Selected Measure Name Company Selected Measure Name U.S. Government Issued Debt Securities (Agency and Treasury) US Government Debt Securities [Member] Accrual for Environmental Loss Contingencies, Beginning Balance Accrual for Environmental Loss Contingencies, Ending Balance Reserve Accrual for Environmental Loss Contingencies Fair Value Measurement [Domain] Fair Value Measurement [Domain] ASSET RETIREMENT OBLIGATIONS Asset Retirement Obligation Disclosure [Text Block] Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Accounts Payable Accounts Payable to Subsidiaries Accounts Payable, Current Operating Cash Flows from Operating Leases Operating Lease, Payments Prior Service Cost Reclassified as Held for Sale Prior Service Cost Reclassification as Held for Sale Prior Service Cost Reclassification as Held for Sale Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] Solar Public Utilities, Property, Plant and Equipment, Generation or Processing Schedule of Defined Contribution Plans Schedule Of Defined Contribution Plans 401k [Table Text Block] Schedule disclosing the matching contributions of cash and NU common shares to the 401k plan. Transmission Support Commitments Transmission Support Commitment Costs Incurred Goodwill [Roll Forward] Goodwill [Roll Forward] COMMITMENTS AND CONTINGENCIES Commitments and Contingencies Disclosure [Text Block] Regulated Operation, Regulatory Asset [Table] Regulated Operation, Regulatory Asset [Table] Distribution - Electric Public Utilities, Property, Plant and Equipment, Distribution Diluted (in shares) Diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Thereafter Recorded Unconditional Purchase Obligation, to be Paid, after Year Five 2007 Series D due 2037 Series D 2007 Notes Due 2037 [Member] Series D 2007 Notes Due 2037 [Member] Weighted-Average Interest Rate as of December 31, Short-Term Debt, Weighted Average Interest Rate, at Point in Time Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] 2018 Series A due 2048 Series A 2018 Notes Due 2048 [Member] Series A 2018 Notes Due 2048 [Member] Number of offshore wind projects Number Of Offshore Wind Projects Number Of Offshore Wind Projects NSTAR Electric Company NSTAR Electric NSTAR Electric Company [Member] Series G of 1968 Preferred Stock at $3.24 Series G of 1968 Preferred Stock at $3.24 [Member] Series G of 1968 Preferred Stock at $3.24 [Member] Entity Small Business Entity Small Business Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Shares outstanding (in shares) Preferred Stock, Shares Outstanding NSTAR Electric Debentures NSTAR Electric Debentures 5.20% [Member] NSTAR Electric Debentures 5.20% State Current State and Local Tax Expense (Benefit) LONG-TERM DEBT Long-Term Debt [Text Block] Document Transition Report Document Transition Report Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] One to five years Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five Eversource Parent - Senior Notes due 2026 - 2050 Eversource Parent - Senior Notes Due 2024 - 2050 [Member] Eversource Parent - Senior Notes Due 2022-2050 Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Preferred stock value outstanding Preferred Stock, Value, Outstanding Future lease payments Finance Lease, Liability, to be Paid Underlying Securities Award Underlying Securities Amount Equity Component [Domain] Equity Component [Domain] Document Period End Date Document Period End Date Original base ROE authorized by FERC at time of complaint Loss Contingency, Original Base ROE Authorized by FERC at Time of Complaint Loss Contingency, Original Base ROE Authorized by FERC at Time of Complaint INCOME TAXES Income Tax Disclosure [Text Block] Restricted stock unit fully vested (in shares) Share Based Compensation Arrangement By Share Based Payment Award Vested Outstanding Number Beginning Balance Ending Balance Accounts Receivable, Allowance for Credit Loss Total construction contract cost Contractual Obligation Offshore Wind Contingent Liability - Current Portion Offshore Wind Contingent Liability, Current Portion Offshore Wind Contingent Liability, Current Portion Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] Current and Long-Term Derivative Liabilities Derivative Liability, Subject to Master Netting Arrangement, before Offset of Collateral [Abstract] Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] First Mortgage Bonds First Mortgage First Mortgage [Member] Transmission Support Commitments Transmission Support Commitments [Member] Valuation allowance for tax credit and operating loss carryforward Tax Credit and Operating Loss Carryforward Valuation Allowance Amount of valuation allowance pertaining to the deferred tax asset representing potential future taxable deductions from tax credit carryforwards and operating loss carryforwards for which it is more likely than not that a tax benefit will not be realized. Eversource Eversource Investment LLC [Member] Eversource Investment LLC Prior Service Cost Reclassified as Held for Sale Other Comprehensive (Income) Loss, Defined Benefit Plan, Cost Reclassified as Held for Sale Other Comprehensive (Income) Loss, Defined Benefit Plan, Cost Reclassified as Held for Sale Document Type Document Type Level 3 Fair Value, Inputs, Level 3 [Member] EARNINGS/(LOSS) PER SHARE Earnings Per Share [Text Block] Name Outstanding Recovery, Individual Name Loss Contingencies [Table] Loss Contingencies [Table] Capital Surplus, Paid In Capital Surplus, Paid in Additional Paid in Capital Product and Service [Axis] Product and Service [Axis] Schedule of Defined Benefit Plans Schedule of Defined Benefit Plans Disclosures [Table Text Block] Notes Payable Borrowings Outstanding as of December 31, Notes Payable Variable Lease Cost Variable Lease, Cost Total Accumulated Depreciation Public Utilities, Property, Plant and Equipment, Accumulated Depreciation Total Current Assets Assets, Current Public utilities, credit to customer payment period Public Utilities, Credit to Customer, Payment Period Public Utilities, Credit to Customer, Payment Period Statistical Measurement [Axis] Statistical Measurement [Axis] Percent of the facility's output required to be purchased Long-Term Contract for Purchase of Electric Power, Share of Plant Output Being Purchased Prior Service Cost Reclassified from Held for Sale Other Comprehensive (Income) Loss, Defined Benefit Plan, Cost Reclassified From Held for Sale Other Comprehensive (Income) Loss, Defined Benefit Plan, Cost Reclassified From Held for Sale Regulatory Asset [Domain] Regulatory Asset [Domain] Capacity and Purchased Power Supply And Stranded Cost Obligations [Member] Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Disposal Group Name [Axis] Disposal Group Name [Axis] South Fork Wind Tax Equity South Fork Wind Tax Equity [Member] South Fork Wind Tax Equity 2025 Series Y due 2028 4.400% Series Y Due 2028 [Member] 4.400% Series Y Due 2028 Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] Power purchase agreement Derivative, Term of Contract Net Income/(Loss) Attributable to Common Shareholders Net Income/(Loss) Attributable to Common Shareholders Net Income/(Loss) Attributable to Common Shareholders Net Income (Loss) Available to Common Stockholders, Basic Regulatory Assets Less:  Current Portion Regulatory Asset, Current Entity Information [Line Items] Entity Information [Line Items] Public utilities, return on rate base, remaining revenue requirement Public Utilities, Return on Rate Base, Remaining Revenue Requirement Public Utilities, Return on Rate Base, Remaining Revenue Requirement Other Comprehensive Income/(Loss), Net of Tax Other Comprehensive Income/(Loss), Net of Tax Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Current Liabilities: Current Liabilities: Liabilities, Current [Abstract] Guarantor Obligations, Nature [Domain] Guarantor Obligations, Nature [Domain] Total Operating Expenses Total Operating Expenses Operating Expenses Borrowings outstanding Long-Term Line of Credit Level 1 Fair Value, Inputs, Level 1 [Member] Period of complaint Loss Contingency, Period of Complaint Loss Contingency, Period of Complaint Goodwill-related Goodwill Regulatory Asset [Member] Goodwill that originated from the merger that created NSTAR in 1999. Redemption Price Per Share (in dollars per share) Preferred Stock, Redemption Price Per Share Diluted Earnings/(Loss) Per Common Share (in dollars per share) Earnings Per Share, Diluted Receivables, Net (net of allowance for uncollectible accounts) Accounts Receivable from Subsidiaries Accounts Receivable, after Allowance for Credit Loss, Current Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Axis] Six to ten years Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 Schedule of Assumptions Used Defined Benefit Plan, Assumptions [Table Text Block] Equity offering (in shares) Sale of Stock, Number of Shares Issued in Transaction Treasury stock, common (in shares) Treasury Stock, Common, Shares State Income Taxes Income Tax Paid, State and Local, after Refund Received Schedule of Asset Retirement Obligation [Table] Schedule of Asset Retirement Obligation [Table] Schedule of Asset Retirement Obligation [Table] Consolidation Items [Domain] Consolidation Items [Domain] Investments, Debt and Equity Securities [Abstract] Investments, Debt and Equity Securities [Abstract] Other Public Utilities, Property, Plant and Equipment, Accumulated Depreciation, Other Public Utilities, Property, Plant and Equipment, Accumulated Depreciation, Other Auditor Location Auditor Location FERC ROE First Complaint FERC ROE First Complaint [Member] FERC ROE First Complaint [Member] INVESTMENTS IN UNCONSOLIDATED AFFILIATES Equity Method Investments and Joint Ventures Disclosure [Text Block] Public utilities, approved rate, gain (loss) on settlement Public Utilities, Approved Rate, Gain (Loss) On Settlement Public Utilities, Approved Rate, Gain (Loss) On Settlement Condensed Balance Sheet Statement [Table] Condensed Balance Sheet Statement [Table] Actuarial (Loss)/Gain Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) Regulatory Liability [Domain] Regulatory Liability [Domain] Less:  Accumulated Depreciation Public Utilities, Property, Plant and Equipment, Net [Abstract] Less amount representing interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount 2026 Rate Reduction Bonds, Principal And Interest Payments To Be Paid, Year One Rate Reduction Bonds, Principal And Interest Payments To Be Paid, Year One Tax Credit Carryforward [Axis] Tax Credit Carryforward [Axis] Milestone Nuclear Power Station Milestone Nuclear Power Station [Member] Milestone Nuclear Power Station [Member] Total Cash Paid/(Received) for Income Taxes, Net of Refunds Income Taxes Income Taxes Paid, Net Corporate Debt Securities Corporate Bond Securities [Member] Water assets reclassified back to marketable securities Water Assets Reclassified Back to Marketable Securities Water Assets Reclassified Back to Marketable Securities Benefit Costs Benefit Costs Benefit Costs [Member] Business combination, transaction cost settlement gain (loss) Business Combination, Transaction Cost Settlement Gain (Loss) Business Combination, Transaction Cost Settlement Gain (Loss) Schedule of Asset Retirement Obligation [Line Items] Schedule of Asset Retirement Obligation [Line Items] [Line Items] for Schedule of Asset Retirement Obligation [Table] Total Current Assets Held for Sale Disposal Group, Including Discontinued Operation, Assets, Current Rate Reduction Bonds Rate Reduction Bonds - Long-Term Portion Rate Reduction Bonds Rate Reduction Bonds FERC ROE Fourth Complaint FERC ROE Fourth Complaint [Member] FERC ROE Fourth Complaint [Member] Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION Property, Plant and Equipment Disclosure [Text Block] Future lease payments Lessee, Operating Lease, Liability, to be Paid Derivative Contract Derivative Asset [Member] Derivative Asset Rate Reduction Bonds – Current Portion Rate Reduction Bonds - Current Portion Rate Reduction Bonds, Current Rate Reduction Bonds, Current Eliminations Eliminations Intersegment Eliminations [Member] Finance Leases: Lessee, Lease, Finance Lease [Abstract] Lessee, Lease, Finance Lease [Abstract] Expiration Date Trading Arrangement Expiration Date Public utilities, requested debt capital structure, percentage Public Utilities, Requested Debt Capital Structure, Percentage Amount outstanding during period Line of Credit Facility, Amount Outstanding During Period Line of Credit Facility, Amount Outstanding During Period Employee Transfers Change In Liability Due To Transfer Of Employees Change in liability due to movement of employees due among operating companies or service companies Fixed Income Fixed Income Securities [Member] Summary of Investments Under the Equity Method Equity Method Investments [Table Text Block] Changes in Unrealized Gains on Marketable Securities Changes in Unrealized Gains on Marketable Securities Other Comprehensive Income (Loss), Available-for-Sale Securities Adjustment, Net of Tax, Portion Attributable to Parent Wholesale Market Sales Revenues Wholesale Market Sales Revenue [Member] Wholesale Market Sales Revenue [Member] 2026 Unrecorded Unconditional Purchase Obligation, to be Paid, Year One Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Materials, Supplies, Natural Gas and REC Inventory Inventory, Policy [Policy Text Block] Additional restricted stock unit expected to vest (in shares) Share Based Compensation Arrangement By Share Based Payment Award Expected To Vest As of the balance sheet date, the number of shares into which expected to vest awards outstanding can be converted under the option plan. Entity Current Reporting Status Entity Current Reporting Status CL&P 2020 Series A First Mortgage Bonds CL&P 0.75% Series A First Mortgage Bonds [Member] CL&P 0.75% Series A First Mortgage Bonds Losses on Offshore Wind Impairment of Ongoing Project Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Consolidated Entities [Domain] Consolidated Entities [Domain] Less than one year Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year One Statutory Federal Income Tax Expense at 21% Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount Period of payment of annual operation and maintenance expense Unrecorded Unconditional Purchase Obligation, Period of Payment of Annual Operation and Maintenance Expense Unrecorded Unconditional Purchase Obligation, Period of Payment of Annual Operation and Maintenance Expense Peaker CfDs Peaker Contracts For Differences Peaker Contracts For Differences [Member] Financial Instrument [Axis] Financial Instrument [Axis] Adjustments to Reconcile Net Income/(Loss) to Net Cash Flows Provided by Operating Activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Noncash Item [Abstract] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Executive Category: Executive Category [Axis] The Connecticut Light and Power Company CL&P The Connecticut Light And Power Company [Member] Asset Retirement Obligations Asset Retirement Obligations, Noncurrent Repayments of Debt Repayments of Debt SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract] SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract] State and Local Income Tax Effects, Net of Federal Impact Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent Fair Value Adjustment Fair Value Adjustment [Member] Eversource TEI LLC Eversource TEI LLC [Member] Eversource TEI LLC Investment Tax Credit Amortization Effective Income Tax Rate Reconciliation, Tax Credit, Investment, Amount Current Portion Finance Lease, Liability, Current Shares issued (in dollars per share) Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Issued In Period Weighted Average Grant Date Fair Value The weighted average grant-date fair value of the number of shares newly issued during the reporting period under the plan. Accumulated benefit obligation Defined Benefit Plan, Accumulated Benefit Obligation Issuance of Long-Term Debt Issuance of Long-Term Debt Proceeds from Issuance of Long-Term Debt Current Fiscal Year End Date Current Fiscal Year End Date Other Regulatory Assets Other Regulatory Assets [Member] Represents various remaining other regulatory assets. Vineyard Wind Project Vineyard Wind Project [Member] Vineyard Wind Project Distribution - Natural Gas Public Utilities Property Plant And Equipment Distribution Natural Gas Period end amount of property, plant and equipment (PPE) related to utility natural gas distribution. Tax Equity Tax Equity [Member] Tax Equity Schedule of Provision for Uncollectible Accounts Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Weighted Average Grant-Date Fair Value Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Shares available for issuance under incentive plan (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant Schedule of Guarantor Obligations Schedule of Guarantor Obligations [Table Text Block] Accounts Payable Disposal Group, Including Discontinued Operation, Accounts Payable Reclassification out of Accumulated Other Comprehensive Income [Domain] Reclassification out of Accumulated Other Comprehensive Income [Domain] Equity Awards Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] 2024 Debentures due 2034 5.400% Notes Due 2034 [Member] 5.400% Notes Due 2034 Renewable Energy Purchase Contracts Renewable Energy Costs Incurred Schedule of Environmental Loss Contingencies by Site Schedule of Environmental Loss Contingencies by Site [Table Text Block] Dividends received from equity method investees Proceeds from Equity Method Investment, Distribution Proceeds from Sales of Marketable Securities Proceeds from Sale and Maturity of Marketable Securities Industrial Industrial [Member] Industrial [Member] Investment tax credit Investment Tax Credit Equity securities Equity Securities, FV-NI, Current Return on equity revenue basis point on reductions Return On Equity Revenue Basis Point On Reductions Return On Equity Revenue Basis Point On Reductions Condensed Balance Sheet Statements, Captions [Line Items] Condensed Balance Sheet Statements, Captions [Line Items] Beginning Balance Ending Balance Unrecognized Tax Benefits Antidilutive share awards excluded from the EPS computation (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Allowance for Funds Used During Construction Allowance for Funds Used During Construction, Policy [Policy Text Block] Weighted Average Common Shares Outstanding: Weighted Average Number of Shares Outstanding, Diluted [Abstract] Total Estimated cost of energy purchase contracts Unrecorded Unconditional Purchase Obligation Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] 2027 Long-Term Debt, Maturity, Year Two Financial Guarantee Financial Guarantee [Member] LEASES Lessee, Operating Leases [Text Block] Amount of natural gas transmission purchased Natural Gas Transition Service Transaction Costs Natural Gas Transition Service Transaction Costs Net Cash Flows Provided by Financing Activities Net Cash Flows (Used In)/Provided by Financing Activities Net Cash Flows Provided by Financing Activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Measure: Measure [Axis] Water Reclassified from Assets Held for Sale Defined Benefit Plan, Reclassification From Assets Held for Sale, Obligation Defined Benefit Plan, Reclassification From Assets Held for Sale, Obligation 2027 Unrecorded Unconditional Purchase Obligation, to be Paid, Year Two RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES Rate Reduction Bonds and Variable Interest Entity Disclosure [Text Block] Rate Reduction Bonds and Variable Interest Entity Disclosure [Text Block] Property, Plant and Equipment, Type [Domain] Long-Lived Tangible Asset [Domain] Long-Term Incentive Plan Activity Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures Yankee Gas Series M First Mortgage Bonds Yankee Gas Series M First Mortgage Bonds [Member] Yankee Gas Series M First Mortgage Bonds Amortization of Actuarial Losses Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member] Disposal Group Classification [Domain] Disposal Group Classification [Domain] Prepayments and Other Current Assets Disposal Group, Including Discontinued Operation, Prepaid and Other Assets, Current Amount of peaking capacity contracts (in MW) Unrecorded Unconditional Purchase Obligation, Amount of Capacity Contracts Unrecorded Unconditional Purchase Obligation, Amount of Capacity Contracts Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Actuarially-Determined Liability Deferred Compensation Cash-Based Arrangements, Liability, Classified, Noncurrent Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Natural Gas Pipeline - Algonquin Gas Transmission, LLC Natural Gas Infrastructure - Pipeline Owned By Enbridge, Inc. [Member] Natural Gas Infrastructure - Pipeline Owned By Enbridge, Inc. [Member] Entity Tax Identification Number Entity Tax Identification Number Proceeds from Sales of Offshore Wind Investments Proceeds from Sale of Equity Method Investments Federal investment tax credits (percent) Effective Income Tax Rate Reconciliation, Tax Credit, Percent Sunrise Wind, LLC Sunrise Wind, LLC [Member] Sunrise Wind, LLC [Member] Summary of the Impact of Funding on the Balance Sheets and Income Statements Schedule of Variable Interest Entities [Table Text Block] Maximum amount of stock to be issued Sale of Stock, Issuance of Common Stock, Maximum Sale of Stock, Issuance of Common Stock, Maximum Issued (in shares) Common Stock, Shares, Issued Total Deferred Credits and Other Liabilities Liabilities, Other than Long-Term Debt, Noncurrent EGMA - First Mortgage Bonds due 2028 - 2052 Aquarion - Unsecured Notes due 2028 - 2052 Unsecured Notes Due 2028-2052 [Member] Unsecured Notes Due 2028-2052 Operating Leases Operating Lease, Weighted Average Remaining Lease Term 2029 Long-Term Debt, Maturity, Year Four Total Regulatory Liabilities Regulatory Liability 2021 Series V due 2031 2.200% Series V Due 2050 [Member] 2.200% Series V Due 2050 Water Goodwill Reclassified from Held for Sale Goodwill, Reclassified as Held for Sale Goodwill, Reclassified as Held for Sale Current Income Taxes: Current Federal, State and Local, Tax Expense (Benefit) [Abstract] Eversource Parent Series H Senior Notes Eversource Parent 3.15% Series H Senior Notes [Member] Eversource Parent 3.15% Series H Senior Notes Payments/Reductions Accrual for Environmental Loss Contingencies, Payments Entity Public Float Entity Public Float Interest Expense Interest Expense on RRB Principal (included in Interest Expense) Interest Expense Interest Expense, Nonoperating Trading Arrangement: Trading Arrangement [Axis] Total Shareholder Return Amount Total Shareholder Return Amount Preferred Stock 4.25% Series of Preferred Stock at 4.25% [Member] Series of Preferred Stock at 4.25% [Member] Lease revenue Operating Lease, Lease Income Complaint period Loss Contingency, Claim Period Loss Contingency, Claim Period Remaining goodwill Goodwill Disposal Group, Including Discontinued Operation, Goodwill, Noncurrent Loss Contingencies [Line Items] Loss Contingencies [Line Items] Actuarial Loss Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax Utility Public Utilities Property Plant And Equipment Electric Natural Gas and Water Utility Total Public Utilities Property Plant And Equipment Electric Natural Gas and Water Utility Total Variable Lease Cost Variable Lease Cost, Decrease Variable Lease Cost, Decrease Other Segment Reporting, Reconciling Item, Corporate Nonsegment [Member] Security Exchange Name Security Exchange Name Preferred Stock 4.78% Series of Preferred Stock at 4.78% [Member] Series of Preferred Stock at 4.78% [Member] Unrealized losses (gain) Marketable Security, Unrealized Gain (Loss) Plant Additions Included in Accounts Payable (As of) Capital Expenditures Incurred but Not yet Paid Maximum borrowing capacity Amount of long-term debt requested for issuance Line of Credit Facility, Maximum Borrowing Capacity Dividends on Preferred Stock Dividends on preferred stock Dividends, Preferred Stock Defined Benefit Plan, Plan Assets, Category [Domain] Defined Benefit Plan, Plan Assets, Category [Domain] Operating Expenses: Operating Expenses: Operating Expenses [Abstract] Other Current Liabilities Accrued Interest (included in Other Current Liabilities) Other Liabilities, Current 2006 Debentures due 2036 Unsecured Notes Due 2036 [Member] Unsecured Notes Due 2036 [Member] Asset Class [Domain] Asset Class [Domain] Discount rate (in percent) Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate Schedule of Weighted-Average AFUDC Rates Schedule Of Allowance For Funds Used During Construction [Table Text Block] EGMA Acquisition and Integration Costs EGMA Acquisition-related Costs [Member] EGMA Acquisition-related Costs Accrued SERP and PBOP Derivative Liabilities Liability, Defined Benefit Plan, Noncurrent Renewable Energy Investment Fund Renewable Energy Investment Fund [Member] Renewable Energy Investment Fund [Member] EDIT due to Tax Cuts and Jobs Act of 2017 Excess ADIT due to tax Cuts and Jobs Act [Member] Excess ADIT due to tax Cuts and Jobs Act [Member] Statement [Line Items] Statement [Line Items] Fair Value Adjustment - Current Portion FairValueAdjustmentMemberCurrentPortion [Member] Settlement Loss Settlement Loss Of Regulatory Asset Settlement Loss Of Regulatory Asset Public utilities, approved equity capital structure, basis point on revenue Public Utilities, Approved Equity Capital Structure, Basis Point On Revenue Public Utilities, Approved Equity Capital Structure, Basis Point On Revenue Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Intercompany Income Allocations Related Intercompany Allocations of Defined (Benefit) Expense Amount represents allocation of pension and other post retirement benefits expense from parent and other that are not included in pension and post-retirement benefit expense. Cash as reported on the Balance Sheets Cash and Cash Equivalent Total Finance Lease Cost Finance Lease, Cost Finance Lease, Cost Other Regulatory Liabilities Other Regulatory Liabilities [Member] Represents various remaining other regulatory liabilities. Common Shares Common Stock Common Stock [Member] Restricted stock units available (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period Percentage of costs or benefits borne under capacity-related contracts (as a percentage) Percentage of Costs or Benefits Borne Under Capacity-Related Contracts Percentage of Costs or Benefits Borne Under Capacity-Related Contracts Finance Leases Finance Lease, Liability, to be Paid, Fiscal Year Maturity [Abstract] Net Increase/(Decrease) in Cash and Restricted Cash Net Increase/(Decrease) in Cash and Restricted Cash Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation Notes Payable to Eversource Parent Notes Payable Notes Payable, Current Goodwill-related Regulatory Asset - 1999 Merger Deferred Tax Liabilities Goodwill Regulatory Asset Collection period Public Utilities, Settlement Period Public Utilities, Settlement Period Guarantor Obligations [Line Items] Guarantor Obligations [Line Items] SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Significant Accounting Policies [Text Block] NSTAR Gas NSTAR Gas Company [Member] NSTAR Gas Company [Member] Statistical Measurement [Domain] Statistical Measurement [Domain] Other Current Assets Other Current Assets [Member] Thereafter Lessee, Operating Lease, Liability, to be Paid, after Year Five Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] 2023 Series B due 2033 2023 Series B due 2033 [Member] 2023 Series B due 2033 Restricted cash, current Restricted Cash, Current Eversource Parent Eversource Parent [Member] Eversource Parent Asset Class [Axis] Asset Class [Axis] Other Long-Term Assets Other Noncurrent Assets [Member] Defined benefit plan, loss due to salary scale assumption Defined Benefit Plan, Loss Due to Salary Scale Assumption Defined Benefit Plan, Loss Due to Salary Scale Assumption Unrealized gain associated with investment Equity in Earnings/(Losses) of Subsidiaries Equity in (Earnings)/Losses of Subsidiaries Income (Loss) from Equity Method Investments 2004 Series B due 2034 Series B 2004 Notes Due 2034 [Member] Series B 2004 Notes Due 2034 [Member] Natural Gas Procurement Natural Gas Procurement Costs Incurred Leases [Abstract] Leases [Abstract] Public Service Company of New Hampshire PSNH Public Service Company Of New Hampshire (PSNH) [Member] Gross Increases - Prior Year Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions Aquarion - Secured Debt due 2027 - 2045 Secured Debt Notes Due 2027- 2045 [Member] Secured Debt Notes Due 2027- 2045 Water Acquisitions Water Acquisitions [Member] Water Acquisitions General obligation bonds General Obligation Bonds General Obligation Bonds Accounts Payable Increase (Decrease) in Accounts Payable Disposal Groups, Including Discontinued Operations Disposal Groups, Including Discontinued Operations [Table Text Block] Concession payment Public Utilities, Concession Payment Public Utilities, Concession Payment Retirement Plan Name [Axis] Retirement Plan Name [Axis] Pre-Tax Unrealized Losses Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] Board Members Board Members [Member] Board Members [Member] Basic Earnings/(Loss) Per Common Share (in dollars per share) Earnings Per Share, Basic Commercial Paper Commercial Paper [Member] Total Inventory, Gross Revolution Wind, LLC and TurbineCo, LLC Revolution Wind, LLC and TurbineCo, LLC [Member] Revolution Wind, LLC and TurbineCo, LLC Liabilities Settled During the Year Asset Retirement Obligation, Liabilities Settled Water Distribution Water Distribution Segment [Member] Water Distribution Segment Capital Additions Adjustment Capital Additions Adjustment [Member] Capital Additions Adjustment NSTAR Electric and EGMA Settlement NSTAR Electric and EGMA Settlement [Member] NSTAR Electric and EGMA Settlement Total Retail Tariff Sales Revenues Total Retail Sales Revenue [Member] Total Retail Sales Revenue [Member] Total Deferred Tax Assets Deferred Tax Assets, Gross Discount Rate Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate Other Comprehensive Income, Net of Tax Other Comprehensive Loss Other Comprehensive Income, Net of Tax Other Comprehensive Income (Loss), Net of Tax Summary of Segment Information and Segmented Total Assets Schedule of Segment Reporting Information, by Segment [Table Text Block] Deferred Income Taxes, Net: Deferred Federal, State and Local, Tax Expense (Benefit) [Abstract] Long-term Contract for Purchase of Electric Power [Axis] Long-Term Contract for Purchase of Electric Power [Axis] Capital Contributions from Eversource Parent Noncontrolling Interest, Increase In Contributions From Parent Noncontrolling Interest, Increase In Contributions From Parent Revisions in Estimated Cash Flows Asset Retirement Obligation, Revision of Estimate Schedule of Available-for-sale Securities Reconciliation Schedule of Available-for-Sale Securities Reconciliation [Table Text Block] FERC ROE Second Complaint FERC ROE Second Complaint [Member] FERC ROE Second Complaint [Member] Series of 1949 Preferred Stock at 3.90% Series of 1949 Preferred Stock at 3.90% [Member] Series of 1949 Preferred Stock at 3.90% [Member] 2028 Finance Lease, Liability, to be Paid, Year Three Employee Benefits Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits Capacity and Purchased Power Supply And Stranded Costs Obligations Incurred Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Eversource Parent Series HH Senior Notes Eversource Parent Series HH Senior Notes [Member] Eversource Parent Series HH Senior Notes Category of Item Purchased [Axis] Category of Item Purchased [Axis] Money Market Funds Cash and Cash Equivalents [Member] Net Realized/Unrealized Losses Included in Regulatory Assets or Regulatory Liabilities Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain (Loss) Included In Regulatory Asset Liability Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain (Loss) Included In Regulatory Asset Liability Variable Interest Entity, Primary Beneficiary Variable Interest Entity, Primary Beneficiary [Member] Eversource Investment LLC, Eversource Investment Service Company LLC and South Fork Class B Member, LLC Eversource Investment LLC, Eversource Investment Service Company LLC and South Fork Class B Member, LLC [Member] Eversource Investment LLC, Eversource Investment Service Company LLC and South Fork Class B Member, LLC Litigation settlement, amount awarded from other party Litigation Settlement, Amount Awarded from Other Party Benefits Paid - SERP Defined Benefit Plan, Payments SERP Defined Benefit Plan payments related to the NU SERP plan Accounts and Financing Receivables [Table] Accounts and Financing Receivables [Table] Investments in Unconsolidated Affiliates Payments to acquire investments Payments to Acquire Equity Method Investments Compensation Expense Share-Based Payment Arrangement, Expense Public Utilities, Regulatory Proceeding [Domain] Public Utilities, Regulatory Proceeding [Domain] Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Goodwill and Intangible Assets Disclosure [Abstract] Current Assets: Current Assets: Assets, Current [Abstract] Catastrophic Storm Costs Catastrophic Storm Costs [Member] Catastrophic Storm Costs Schedule of Utility Property, Plant and Equipment Public Utility Property, Plant, and Equipment [Table Text Block] Total Liabilities and Capitalization Liabilities and Equity Defined Benefit Plans Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Related tax effect recognized in AOCI Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, Tax 2029 Rate Reduction Bonds, Principal And Interest Payments To Be Paid, Year Four Rate Reduction Bonds, Principal And Interest Payments To Be Paid, Year Four Distribution - Natural Gas Distribution Natural Gas Useful Life Distribution Natural Gas Useful Life Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Amount of power to be purchased under capacity-related contract (up to) (in MW) Amount of Capacity Provided Under Capacity Contract Amount of Capacity Provided Under Capacity Contract Amounts Reclassified from AOCI Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent Real Assets Employee Benefit Plan, Real Estate [Member] Other Deferred Tax Assets, Other Accrued SERP and PBOP Liability, Defined Benefit Plan Equity Method Investment [Table] Equity Method Investment [Table] Cash Flows Used for Investments in Plant Segment, Expenditure, Addition to Long-Lived Assets Accounting Policies [Abstract] Accounting Policies [Abstract] Future Minimum Lease Payments under Long-Term Operating Leases Lessee, Operating Lease, Liability, to be Paid, Maturity [Table Text Block] Treasury Stock Treasury Stock, Common [Member] Pay vs Performance Disclosure [Line Items] Summary of Goodwill by Reportable Segment Business Combination, Goodwill, Reportable Segment Assignment [Table Text Block] Total Operating Lease Liabilities Present value of future minimum lease payments Operating Lease, Liability Residential Residential [Member] Residential [Member] Amortization of Right-of-use-Assets Finance Lease, Right-of-Use Asset, Amortization Employee Transfers Change In Assets Due To Transfer Of Employees Change in assets due to the merger of the service companies or transfer to employees among operating companies Accrued interest payable Income Tax Examination, Penalties and Interest Accrued Other Long-Term Liabilities Other Liabilities, Noncurrent Auditor [Line Items] Auditor [Line Items] Series of 1967 Preferred Stock at 5.28% Series of 1967 Preferred Stock at 5.28% [Member] Series of 1967 Preferred Stock at 5.28% [Member] Goodwill impairment charge Goodwill, impairment loss Water Goodwill Impairment Goodwill impairment Goodwill, Impairment Loss Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Long-Term Debt – Current Portion Less Amounts due Within One Year Long-Term Debt, Current Maturities Company Selected Measure Amount Company Selected Measure Amount 2028 Lessee, Operating Lease, Liability, to be Paid, Year Three Employer Contributions Employer Contributions Defined Benefit Plan, Plan Assets, Contributions by Employer Cash Cash Comprehensive Income/(Loss) Attributable to Common Shareholders Comprehensive Income/(Loss) Comprehensive Income (Loss), Net of Tax, Attributable to Parent Renewal period Lessee, Operating And Finance Lease, Renewal Term Lessee, Operating And Finance Lease, Renewal Term 2025 Debentures due 2030 4.850% Notes Due 2030 [Member] 4.850% Notes Due 2030 Disposal Group Name [Domain] Disposal Group Name [Domain] Name Measure Name 2016 Debentures due 2026 Unsecured Notes Due 2026 [Member] Unsecured Notes Due 2026 [Member] Less than one year Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One Secured Debt Secured Debt [Member] 2020 Series A due 2025 Series A 2020 Notes Due 2025 [Member] Series A 2020 Notes Due 2025 Class of Stock [Line Items] Class of Stock [Line Items] Accumulated Deferred Income Taxes Deferred Income Tax Liabilities, Net Expected Long-Term Rate of Return (in percent) Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-Term Rate of Return on Plan Assets Unsecured Debt Unsecured Debt Unsecured Debt [Member] EGMA Series F First Mortgage Bonds EGMA Series F First Mortgage Bonds [Member] EGMA Series F First Mortgage Bonds SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Table] SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Table] Yankee Gas - First Mortgage Bonds due 2026 - 2051 Unsecured Notes Due 2026-2051 [Member] Unsecured Notes Due 2018-2044 [Member] Accounts Payable to Subsidiaries Increase (Decrease) in Accounts Payable, Related Parties Refund payments Proceeds from Customers Depreciation Effective Income Tax Rate Reconciliation, Nondeductible Expense, Depreciation, Amount Period of graded vesting schedule under long-term incentive program Period of Graded Vesting Schedule Under Long-Term Incentive Program Period of Graded Vesting Schedule Under Long-Term Incentive Program Eversource Parent Series Q Senior Notes Eversource Parent 0.80% Series Q Senior Notes [Member] Eversource Parent 0.80% Series Q Senior Notes Income Tax Contingency [Table] Income Tax Contingency [Table] Long-Term Debt Long-Term Debt Schedule of Amounts Reclassified from AOCI by Component Comprehensive Income (Loss) [Table Text Block] Legal Entity [Axis] Legal Entity [Axis] Total Assets Total Assets (as of) Assets Uncategorized Defined Benefit Plan, Fair Value of Plan Assets, Uncategorized Defined Benefit Plan, Fair Value of Plan Assets, Uncategorized Income Taxes, Net Deferred Income Tax Charge [Member] Total Deferred Debits and Other Assets Assets, Noncurrent, Other than Noncurrent Investments and Property, Plant and Equipment Weighted average grant date fair value of restricted stock units (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Regulatory Liability [Axis] Regulatory Liability [Axis] Geographical [Domain] Geographical [Domain] Other Taxes Income Tax, Policy [Policy Text Block] Financing Receivable, Allowance for Credit Loss [Roll Forward] Financing Receivable, Allowance for Credit Loss [Roll Forward] Operating Activities: Operating Activities: Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Receivable Type [Axis] Receivable Type [Axis] Research and Development Tax Credits Effective Income Tax Rate Reconciliation, Tax Credit, Research, Percent Natural Gas Procurement Natural Gas Procurement Contracts [Member] Public utilities, credit to customer Public Utilities, Credit to Customer Public Utilities, Credit to Customer New general obligation bonds to fund the electric vehicle charging program New General Obligation Bonds to Fund the Electric Vehicle Charging Program New General Obligation Bonds to Fund the Electric Vehicle Charging Program Tax Effect - Tax Regulatory Assets Deferred Tax Liabilities Regulatory Assets Tax Effect Tax Regulatory Assets South Fork Class B Member, LLC South Fork Class B Member, LLC [Member] South Fork Class B Member, LLC Private Equity Private Equity   Private Equity Funds [Member] Derivative Contracts Regulatory Assets Offsetting Derivative Liabilities [Member] The regulatory assets offsetting derivative liabilities relate to the fair value of contracts used to purchase power and other related contracts that will be collected from customers in the future. Marketable Securities Marketable Securities [Member] Marketable Securities [Member] Energy price Energy Price Energy Price 2026 Finance Lease, Liability, to be Paid, Year One Dividends on ESOP Effective Income Tax Rate Reconciliation, Deduction, Employee Stock Ownership Plan Dividend, Amount Dividends on Common Shares (in dollars per share) Common Stock, Dividends, Per Share, Declared Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Decrease in liability as a result of a change in discount rate Defined Benefit Plan, Decrease of Liability As A Result of Change in Discount Rate Defined Benefit Plan, Decrease of Liability As A Result of Change in Discount Rate Lease, Cost [Abstract] Lease, Cost [Abstract] Accrual for Environmental Loss Contingencies [Roll Forward] Accrual for Environmental Loss Contingencies [Roll Forward] Debt Securities, Available-for-sale [Line Items] Debt Securities, Available-for-Sale [Line Items] Impact of the rate, pre-tax benefit to earnings Impact of the Rate, Pre-Tax Benefit to Earnings Impact of the Rate, Pre-Tax Benefit to Earnings Level 2 Fair Value, Inputs, Level 2 [Member] Repayment of Rate Reduction Bonds Repayments Of Rate Reduction Bonds Repayments Of Rate Reduction Bonds Document Financial Statement Error Correction [Flag] Document Financial Statement Error Correction [Flag] State Income Taxes, Net of Federal Impact State expense (benefit) tax credits Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount 2016 Senior Notes Series H due 2026 Series H Notes Due 2026 [Member] Series H Notes Due 2026 [Member] Schedule of Components of Regulatory Assets Schedule of Regulatory Assets [Table Text Block] SHORT-TERM DEBT Short-Term Debt [Text Block] Uncollectible Expense Operation Uncollectible Expenses Incurred Operation Uncollectible Expenses Incurred Investments in Unconsolidated Affiliates Equity Method Investments Equity Method Investments Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Business Combination [Domain] Business Combination [Domain] Operating Leases Lessee, Operating Lease, Liability, to be Paid, Fiscal Year Maturity [Abstract] Related Party Related Party [Member] Additions, Charged to Other Accounts SEC Schedule, 12-09, Valuation Allowances and Reserves, Additions, Charge to Other Account Components of Income Tax Expense Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Allowance for Uncollectible Accounts Deferred Tax Asset, Tax Deferred Expense, Reserve and Accrual, Accounts Receivable, Allowance for Credit Loss Plan Name [Axis] Plan Name [Axis] PEO PEO [Member] Loss contingency, pending claims, number Loss Contingency, Pending Claims, Number Total Long Term Debt Maturities Repayments Of Principal Total Amount of long-term debt maturities at the date of the latest balance sheet presented in the financial statements, which may include maturities of long-term debt, sinking fund requirements, and other securities redeemable at fixed of determinable prices and dates. Investments Classified by Contractual Maturity Date Investments Classified by Contractual Maturity Date [Table Text Block] 401 PBOP Assets Assetsrelatedto401h [Member] Interest Income Investment Income, Interest 2021 Series A due 2031 Series A 2021 Notes Due 2031 [Member] Series A 2021 Notes Due 2031 2004 Senior Notes Series B due 2034 Series B Notes Due 2034 [Member] Series B Notes Due 2034 [Member] Changes in Current Assets and Liabilities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract] Total Rate Reduction Bonds, Principal And Interest Payments To Be Paid Rate Reduction Bonds, Principal And Interest Payments To Be Paid Schedule of Supplemental Cash Flow [Table] Schedule of Supplemental Cash Flow [Table] Schedule of Supplemental Cash Flow [Table] 2024 Series B due 2034 2024 Series B due 2034 [Member] 2024 Series B due 2034 Tax Asset Valuation   Allowance/Reserve Adjustments Charge of valuation allowance Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount Accelerated Depreciation and Other   Plant-Related Differences Deferred Tax Liabilities, Property, Plant and Equipment NSTAR Electric Debentures NSTAR Electric Debentures 4.85% [Member] NSTAR Electric Debentures 4.85% Regulatory Deferrals - Assets Deferred Tax Liabilities Regulatory Assets Other Regulatory Deferrals Retained Earnings Retained Earnings [Member] Property, Plant and Equipment, Net Property Plant And Equipment Net Excluding Construction Work In Progress Period end amount of property, plant and equipment (PPE) related to utility distribution. Income Tax Jurisdiction [Axis] Income Tax Jurisdiction [Axis] Components of Other Operating Costs and Expense [Table] Components of Other Operating Costs and Expense [Table] Components of Other Operating Costs and Expense [Table] Cash and Restricted Cash - Beginning of Year Cash and Restricted Cash - End of Year Cash and Restricted Cash as reported on the Statements of Cash Flows Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Income Statement [Abstract] Income Statement [Abstract] Derivative Assets Derivative Asset Series of 1949 Preferred Stock at $2.20 Series of 1949 Preferred Stock at $2.20 [Member] Series of 1949 Preferred Stock at $2.20 [Member] Change in Pension Plan Assets: Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract] OCI Before Reclassifications OCI, before Reclassifications, before Tax, Attributable to Parent Purchases of Marketable Securities Payments to Acquire Marketable Securities Performance Guarantee Performance Guarantee [Member] Defined Contribution Plan, Alternate Contribution 401K Defined Contribution Plan, Alternate Contribution 401K [Member] Defined Contribution Plan, Alternate Contribution 401K [Member] Permanent annual base distribution rate increase Permanent Annual Base Distribution Rate Increase Permanent Annual Base Distribution Rate Increase Derivative Liabilities Derivative Liability, Noncurrent Total Marketable Securities Investments, Fair Value Disclosure 2025 Series A due 2030 2025 Series A due 2030 [Member] 2025 Series A due 2030 Product and Service [Domain] Product and Service [Domain] Other Other [Member] Other [Member] Amortization Amortization, Including Amortization Of Regulatory Asset (Liability) Amortization, Including Amortization Of Regulatory Asset (Liability) Pending redemption Defined Benefit Plan, Plan Assets, Pending Redemption Defined Benefit Plan, Plan Assets, Pending Redemption Asset Retirement Obligation Disclosure [Abstract] Asset Retirement Obligation Disclosure [Abstract] EDIT Amortization Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amortization, Percent Net Income/(Loss) Net Income/(Loss) Net Income/(Loss) Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Series E of 1954 Preferred Stock at $2.06 Series E 1954 Preferred Stock at $2.06 [Member] Series E 1954 Preferred Stock at $2.06 [Member] Assumed Rate of Return on Defined Benefit Plan Assets Assumed Rate of Return on Defined Benefit Plan Assets Represents the assumed rate of return for each class of pension and other post retirement benefit plan assets Equity Funds Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity Series of 1947 Preferred Stock at $2.00 Series of 1947 Preferred Stock at $2.00 [Member] Series of 1947 Preferred Stock at $2.00 [Member] Operating Lease, Lease Income, Statement of Income or Comprehensive Income [Extensible Enumeration] Operating Lease, Lease Income, Statement of Income or Comprehensive Income [Extensible Enumeration] Hydro-Québec Hydro-Québec [Member] Hydro-Québec EDIT Amortization Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amortization, Amount City Area Code City Area Code Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] Decrease in valuation allowance Valuation Allowance, Deferred Tax Asset, Decrease, Amount Valuation Allowance, Deferred Tax Asset, Decrease, Amount Settlements Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements Maximum loans receivable outstanding Maximum Loans Receivable Outstanding Maximum Loans Receivable Outstanding Cost sharing agreement, threshold amount Cost Sharing Agreement, Threshold Amount Cost Sharing Agreement, Threshold Amount Debt Securities, Trading, and Equity Securities, FV-NI [Table] Debt Securities, Trading, and Equity Securities, FV-NI [Table] Inflation Based Adjustment Inflation Based Adjustment [Member] Inflation Based Adjustment Private Debt Defined Benefit Plan, Debt Security, Private Debt [Member] Defined Benefit Plan, Debt Security, Private Debt [Member] Total Deferred Tax Liabilities Deferred Tax Liabilities, Net Corporate Shared Services, (General and Administrative) General and Administrative Expense Investing Activities: Investing Activities: Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] Series of 1947 Preferred Stock at $1.90 Series of 1947 Preferred Stock at $1.90 [Member] Series of 1947 Preferred Stock at $1.90 [Member] Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Employer matching contribution (as a percentage) Defined Contribution Plan, Employer Matching Contribution, Percent of Match SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain] SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain] Investment Tax Credits, Net Tax Adjustments, Settlements, and Unusual Provisions Prior Service (Credit)/Cost Regulatory Asset Prior Service Cost Amount related to the pretax cost of benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation, which has not yet been recognized as components of net periodic benefit cost. Actuarial Loss/(Gain) Defined Benefit Plan, Amortization of Gain (Loss) Short-term debt, paid Short-Term Debt, Other, Average Rate Paid Total Lease Cost Lease, Cost Cash Balance Interest Crediting Rate Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Weighted-Average Interest Crediting Rate Natural Gas Natural Gas [Member] Goodwill Beginning Balance Ending Balance Goodwill Loss contingency, estimate of possible earnings impact Loss Contingency, Estimate of Possible Loss Components of Lease Cost Lease, Cost [Table Text Block] Special Deposits Current Derivative Assets: Prepaid Expenses and Other Current Assets [Member] Federal Deferred Federal Income Tax Expense (Benefit) Current Assets Held for Sale Asset, Held-for-Sale, Not Part of Disposal Group, Current Accrued liability, defined benefit pension plan Liability, Defined Benefit Pension Plan, Noncurrent Unrecognized Tax Benefits [Roll Forward] Unrecognized Tax Benefits [Roll Forward] Current Liabilities Held for Sale Liabilities Held-for-sale, Not Part of Disposal Group, Current Liabilities Held-for-sale, Not Part of Disposal Group, Current Auditor Name Auditor Name Settlement Losses Accumulated Defined Benefit Plans Adjustment, Settlement Loss Attributable To Parent [Member] Accumulated Defined Benefit Plans Adjustment, Settlement Loss Attributable To Parent Operations, Excluding Storm Costs Operation Costs and Expenses, Excluding Storm Operation Costs and Expenses, Excluding Storm Construction Work in Progress Public Utilities, Property, Plant and Equipment, Construction Work in Progress Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income Amortization Prior Service Cost From RegAsset The change in other regulatory asset due to the amortization of the net prior service costs (credit) into net periodic pension costs. Deferred Credits and Other Liabilities: Other Liabilities, Noncurrent [Abstract] Yankee Gas Yankee Gas [Member] Yankee Gas Regulatory Liabilities Disposal Group, Including Discontinued Operation, Regulatory Liabilities Disposal Group, Including Discontinued Operation, Regulatory Liabilities Yankee Gas, NSTAR Gas and EGMA Yankee Gas, NSTAR Gas And EGMA [Member] Yankee Gas, NSTAR Gas And EGMA Supplemental Cash Flow Information: Supplemental Cash Flow Information [Abstract] Capital Loss Carryforward Capital Loss Carryforward [Member] Summary of Tax Credits and Loss Carryforwards Summary of Operating Loss Carryforwards [Table Text Block] Amortized Cost Debt Securities, Available-for-Sale, Amortized Cost Other Performance Measure, Amount Other Performance Measure, Amount Schedule of Cash and Cash Equivalents as Reported on the Balance Sheet Restrictions on Cash and Cash Equivalents [Table Text Block] Collection period Public Utilities, Collection Period Public Utilities, Collection Period Payments for charitable contributions Payments For Charitable Contributions Payments For Charitable Contributions Actuarial Loss/(Gain) Arising During the Year Gain Loss Arising During Year Regulatory Pretax change in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan, that has not been recognized in net periodic benefit cost. Related and Nonrelated Parties [Domain] Related and Nonrelated Parties [Domain] Income Tax Expense (Benefit), Effective Income Tax Rate Reconciliation, Amount [Abstract] Income Tax Expense (Benefit), Effective Income Tax Rate Reconciliation, Amount [Abstract] Real Assets Real Estate [Member] Current Derivative Liabilities: Other Current Liabilities [Member] Benefits Paid - Pension Defined Benefit Plan, Plan Assets, Benefits Paid Fair Value Measurements Fair Value of Financial Instruments, Policy [Policy Text Block] Contract term (in years) Contractual Obligation, Term Of Contract Contractual Obligation, Term Of Contract LEASES Lessee, Finance Leases [Text Block] Prepayments and Other Current Assets Prepayments and Other Current Assets, Including Assets Held for Sale Other Assets, Current Entity [Domain] Entity [Domain] Net Cash Flows Used in Investing Activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Materials and Supplies Materials and Supplies [Member] Materials and Supplies [Member] Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table [Member] Loss on Pending Sale of Aquarion Loss on Pending Sale of Aquarion Gain (Loss) on Disposition of Business Renewable Energy Purchase Contracts Renewable Energy Contracts [Member] Interest, Net of Amounts Capitalized Interest Interest Paid, Excluding Capitalized Interest, Operating Activity Document Fiscal Year Focus Document Fiscal Year Focus Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Right-of-use-Assets, Net Operating Lease, Right-of-Use Asset Loans transferred receivable current Notes Receivable from Subsidiaries Financing Receivable, after Allowance for Credit Loss, Current Rate Reduction Bonds and Variable Interest Entity [Abstract] Rate Reduction Bonds and Variable Interest Entity [Abstract] Rate Reduction Bonds and Variable Interest Entity [Abstract] Effective Income Tax Rate Reconciliation, Percent Effective Income Tax Rate Reconciliation, Percent Depreciation Effective Income Tax Rate Reconciliation, Nondeductible Expense, Depreciation, Percent Operating Lease Cost Operating Lease, Cost Gross Decreases - Prior Year Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions Carrying Amount Fair Value Adjustment Reported Value Measurement [Member] Eversource Investment Services Company LLC Eversource Investment Services Company LLC [Member] Eversource Investment Services Company LLC Plan Name [Domain] Plan Name [Domain] Accounts Receivable from EGMA for Acquisition and Integration Costs Allowed for Recovery Increase (Decrease) in Accounts Receivable, Related Parties Period for recognition Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Taxes Other Than Income Taxes Taxes, Miscellaneous FERC ROE First, Second and Third Complaints FERC ROE First, Second and Third Complaints [Member] FERC ROE First, Second and Third Complaints [Member] Yankee Companies Yankee Companies [Member] Less: Valuation Allowance Deferred Tax Assets, Valuation Allowance Equity: Equity [Abstract] Non-United States Defined Benefit Plan, Equity Securities, Non-US [Member] Buildings Building [Member] Components of Other Operating Costs and Expense [Line Items] Components of Other Operating Costs and Expense [Line Items] [Line Items] for Components of Other Operating Costs and Expense [Table] Derivative Accounting Derivatives, Policy [Policy Text Block] SEGMENT INFORMATION Segment Reporting Disclosure [Text Block] Goodwill [Table] Goodwill [Table] 2028 Unrecorded Unconditional Purchase Obligation, to be Paid, Year Three 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] United States Treasuries US Treasury Securities [Member] Fair Value of Plan Assets as of Beginning of Year Fair Value of Plan Assets as of End of Year Fair value of pension plan assets Defined Benefit Plan, Plan Assets, Amount Federal Current Federal Tax Expense (Benefit) Short-term debt borrowing calculation approved by regulatory agency Short-Term Debt Borrowing Calculation Approved By Regulatory Agency Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Rate increase approved Public Utilities, Approved Rate Increase (Decrease), Amount Series of 1949 Preferred Stock at $2.04 Series of 1949 Preferred Stock at $2.04 [Member] Series of 1949 Preferred Stock at $2.04 [Member] AFUDC Equity AFUDC Equity [Member] AFUDC Equity [Member] Schedule of Net Benefit Costs Schedule of Net Benefit Costs [Table Text Block] Other Fixed Income Securities Other Debt Obligations [Member] Qualified Cash Flow Hedging Instruments Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax, Parent Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] Water Reclassified from Assets Held for Sale Defined Benefit Plan, Reclassification From Assets Held for Sale, Pension Plan Assets Defined Benefit Plan, Reclassification From Assets Held for Sale, Pension Plan Assets ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) Comprehensive Income (Loss) Note [Text Block] Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Hydro-Quebec System Hydro-Quebec System [Member] Hydro-Quebec System [Member] Weighted Average Weighted Average [Member] CL&P 2025 Series A First Mortgage Bonds CL&P 4.95% Series A First Mortgage Bonds [Member] CL&P 4.95% Series A First Mortgage Bonds Assets Held for Sale Accounts Receivable, Due to Assets Held for Sale Accounts Receivable, Due to Assets Held for Sale Accumulated Deferred Income Taxes Deferred Income Tax Assets, Net Changes in Accumulated Other Comprehensive Income/(Loss) by Component, Net of Tax Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Depreciation and Amortization Depreciation, Depletion and Amortization Preferred stock, dividend rate, per-dollar-amount (in dollars per share) Preferred Stock, Dividend Rate, Per-Dollar-Amount Short Term Debt Authorization Calculation Short Term Debt Authorization Calculation [Member] Short Term Debt Authorization Calculation [Member] Taxes Receivable/Accrued, Net Taxes Receivable/Accrued, Net Increase (Decrease) in Income Taxes Receivable Loans transferred receivable non-current Notes Receivable from Subsidiaries Financing Receivable, after Allowance for Credit Loss, Noncurrent Settlement Loss Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement Consideration received from sale of stock Sale of Stock, Consideration Received on Transaction 2007 Series B due 2037 Series B 2007 Notes Due 2037 [Member] Series B 2007 Notes Due 2037 [Member] Interest included in payment to settle spent nuclear fuel obligation Interest included in payment to settle spent nuclear fuel obligation Amount represents the interest included in the payment to settle the spent nuclear fuel obligation Additions Accrual for Environmental Loss Contingencies, Charges to Expense for New Losses Schedule of Costs Related to Fuel and Natural Gas Schedule of Fuel Costs [Table Text Block] Total Finance Lease Liabilities Present value of future minimum lease payments Finance Lease, Liability Arrangement Duration Trading Arrangement Duration Segments [Axis] Segments [Axis] High Yield Fixed Income Defined Benefit Plan, Debt Security, Public High Yield Fixed Income [Member] Defined Benefit Plan, Debt Security, Public High Yield Fixed Income [Member] Derivative Liabilities Deferred Tax Assets, Derivative Instruments Local Phone Number Local Phone Number Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Series of 1956 Preferred Stock at 4.5% Series of 1956 Preferred Stock at 4.5% [Member] Series of 1956 Preferred Stock at 4.5% [Member] Other Investing Activities Other Investing Activities Payment for (Proceeds from) Other Investing Activity Thereafter Long-Term Debt, Maturity, after Year Five ASSETS ASSETS Assets [Abstract] Series of 1958 Preferred Stock at 4.96% Series of 1958 Preferred Stock at 4.96% [Member] Series of 1958 Preferred Stock at 4.96% [Member] Credit Facility [Axis] Credit Facility [Axis] Underlying Security Market Price Change Underlying Security Market Price Change, Percent Number of companies that transmit hydro electricity imported from The Hydro-Quebec System in Canada Number of Companies That Transmit Hydro Electricity Number of Companies That Transmit Hydro Electricity Debt Instrument [Axis] Debt Instrument [Axis] Forfeited (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value FAIR VALUE OF FINANCIAL INSTRUMENTS Fair Value Disclosures [Text Block] Increase/(Decrease) in Notes Receivable from Subsidiaries Increase (Decrease) In Notes Receivable From Affiliates Increase (Decrease) In Notes Receivable From Affiliates Number of sites Number of sites Environmental Site Quantity Number of environmental sites by NU Entity in the remediation or long-term monitoring phase Credit Facility [Domain] Credit Facility [Domain] Common Shareholders' Equity: Equity, Attributable to Parent [Abstract] Derivative Liabilities Derivative Liability, Current Equity in Earnings Of Unconsolidated Affiliate Equity in Earnings Of Unconsolidated Affiliate [Member] Equity in Earnings Of Unconsolidated Affiliate Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment and Tax Long-Term Assets Held for Sale Long-Term Assets Held for Sale, Noncurrent Long-Term Assets Held for Sale, Noncurrent Interest Rate Debt Instrument, Interest Rate, Stated Percentage Investment, Name [Axis] Investment, Name [Axis] Computer Software, Hardware and Equipment Computer Software, Hardware And Equipment [Member] Computer Software, Hardware And Equipment [Member] Long-Term Operating Lease, Liability, Noncurrent Entity Voluntary Filers Entity Voluntary Filers Property, Plant and Equipment, Net Disposal Group, Including Discontinued Operation, Property, Plant and Equipment, Noncurrent Equity method investment, other than temporary impairment, after tax Equity method investment, other than temporary impairment, after tax Equity Method Investment, Other than Temporary Impairment, After Tax Equity Method Investment, Other than Temporary Impairment, After Tax Commodity Supply and Price Risk Management Derivative Asset, Subject to Master Netting Arrangement, before Offset Storm Costs, Net Storm Restoration Costs [Member] The storm cost deferrals relate to costs incurred by the regulated company for restorations that met regulatory agency specified criteria for deferral to a major storm cost reserve. FERC ROE Complaints FERC ROE Complaints [Member] FERC ROE Complaints [Member] Property, Plant and Equipment [Abstract] Property, Plant and Equipment [Abstract] Entity Registrant Name Entity Registrant Name Percentage of base ROE reasonably justified Loss Contingency, Percentage Of Base ROE Reasonably Justified Loss Contingency, Percentage Of Base ROE Reasonably Justified Prior Service Cost Arising During the Year Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), before Tax Retirement Plan Name [Domain] Retirement Plan Name [Domain] Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Retained earnings subject to restrictions Retained Earnings, Unappropriated Total Net Periodic Benefit Plan Income Defined Benefit Plan, Net Periodic Benefit Cost (Credit) 2015 Series A due 2045 Series A 2015 Notes Due 2045 [Member] Series A 2015 Notes Due 2045 [Member] Municipal Bonds Municipal Bonds [Member] Transfer of Energy Efficiency Loans Loan Commitments, Policy [Policy Text Block] Regulated Operations [Abstract] Regulated Operations [Abstract] Regulatory Deferrals - Liabilities Deferred Tax Assets, Regulatory Assets and Liabilities Other State and Local Tax Jurisdiction, Other [Member] Capital Stock Expense Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs Consolidated total debt to total capital ratio (as a percentage) Ratio of Indebtedness to Net Capital 2015 Debentures due 2025 Unsecured Notes Due 2025 [Member] Unsecured Notes Due 2025 [Member] AFUDC - Transmission AFUDC Transmission Incentive [Member] AFUDC is recorded on 100 percent of CL&P's and WMECO's CWIP for their NEEWS projects, all of which is being reserved as a regulatory liability to reflect current rate base recovery for 100 percent of the CWIP as a result of FERC-approved transmission incentives. Schedule of Borrowings Outstanding Schedule of Outstanding Long-Term Debt Schedule of Debt [Table Text Block] Granted (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Interest Cost Defined Benefit Plan, Interest Cost Related and Nonrelated Parties [Axis] Related and Nonrelated Parties [Axis] Weighted-Average Remaining Lease Term (Years): Lessee, Lease, Weighted Average Remaining Lease Term [Abstract] Lessee, Lease, Weighted Average Remaining Lease Term [Abstract] FERC ROE Complaints FERC ROE First and Second Complaints [Member] FERC ROE First and Second Complaints [Member] Long-Term Derivative Liabilities: Other Noncurrent Liabilities [Member] Type Of Inventory By Major Asset Class Member [Domain] Type Of Inventory By Major Asset Class Member [Domain] Type of inventory by major asset class Restatement Determination Date: Restatement Determination Date [Axis] Schedule of Other Taxes Schedule of Gross Earnings Taxes [Table Text Block] Schedule of Gross Earnings Taxes [Table Text Block] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] 2027 Recorded Unconditional Purchase Obligation, to be Paid, Year Two Other Financing Activities Other Financing Activities Proceeds from (Payment for) Other Financing Activity Non-Cash Investing Activities: Additional Cash Flow Elements, Investing Activity [Abstract] Regulatory Asset [Axis] Regulatory Asset [Axis] Effective income tax rate reconciliation, change in enacted tax rate, amount Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount Name Trading Arrangement, Individual Name Prepaid asset Defined Benefit Plan, Prepaid Assets Defined Benefit Plan, Prepaid Assets Cumulative pre-tax reserves which include impact of refunds given to customers Loss Contingency, Cumulative Pre-Tax Reserves Which Include Impact of Refunds Given to Customers Loss Contingency, Cumulative Pre-Tax Reserves Which Include Impact of Refunds Given to Customers Other Retirement Benefits Expense Deferred Compensation Cash-based Arrangements, Expense Pertaining to Deferred Benefits Other retirement benefits are accounted for on an accrual basis and expensed over the service lives of the employees in accordance with accounting guidance for deferred compensation contracts. Schedule of Short-term Debt [Table] Short-Term Debt [Table] Emerging Markets Defined Benefit Plan, Equity Securities, Emerging Markets [Member] Defined Benefit Plan, Equity Securities, Emerging Markets [Member] Face amount of debt Amount of securitized rate reduction bonds issued Debt Instrument, Face Amount Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] PSNH Series Y First Mortgage Bonds PSNH Series Y First Mortgage Bonds [Member] PSNH Series Y First Mortgage Bonds Name Awards Close in Time to MNPI Disclosures, Individual Name EGMA Series EGMA Series [Member] EGMA Series Weighted average shares outstanding (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Restricted cash, noncurrent Restricted Cash, Noncurrent Acquisition and Integration Costs Allowed for Recovery Gain (Loss) On Settlement Of Acquisition and Integration Costs Gain (Loss) On Settlement Of Acquisition and Integration Costs Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Condensed Statement of Comprehensive Income [Table] Condensed Statement of Comprehensive Income [Table] Regulatory Assets Total Long-Term Regulatory Assets Regulatory Asset, Noncurrent ICFR Auditor Attestation Flag ICFR Auditor Attestation Flag Other, Net Other, Net Percentage of employees' pay (up to) Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay Issuance of Treasury Shares (in shares) Stock Issued During Period, Shares, Treasury Stock Reissued Total AFUDC Allowance For Funds Used During Construction Total value of the public utilities allowance for funds used during construction capitalized portions, including both the equity and debt portions Treasury Stock Treasury Stock, Value Future Minimum Lease Payments under Long-Term Finance Leases Finance Lease, Liability, to be Paid, Maturity [Table Text Block] Excise and sales taxes Excise and Sales Taxes Fixed Income Fixed Income Funds [Member] Defined Contribution Plan Disclosure [Line Items] Defined Contribution Plan Disclosure [Line Items] Litigation Case [Axis] Litigation Case [Axis] Prior Service Cost Reclassified from Held for Sale Prior Service Cost Reclassification From Held for Sale Prior Service Cost Reclassification From Held for Sale Auditor Firm ID Auditor Firm ID Segments [Domain] Segments [Domain] Damages sought Loss Contingency, Damages Sought, Value Water Distribution Eversource Water [Member] Eversource Water [Member] Available Borrowing Capacity as of December 31, Line of Credit Facility, Remaining Borrowing Capacity Pending purchases and pending redemption settlements Defined Benefit Plan, Plan Assets, Pending Purchases and Pending Redemption Settlement Defined Benefit Plan, Plan Assets, Pending Purchases and Pending Redemption Settlement MARKETABLE SECURITIES Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Environmental Loss Contingency, Statement of Financial Position [Extensible Enumeration] Environmental Loss Contingency, Statement of Financial Position [Extensible Enumeration] Benefit Obligation as of Beginning of Year Benefit Obligation as of End of Year Defined Benefit Plan, Benefit Obligation Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Final proposed rate increase Final Proposed Rate Increase Final Proposed Rate Increase Statement of Financial Position Location, Balance [Domain] Statement of Financial Position Location, Balance [Domain] Noncontrolling Interest - Preferred Stock of Subsidiaries Preferred Stock Not Subject to Mandatory Redemption Noncontrolling interest - preferred stock of subsidiaries Redeemable Noncontrolling Interest, Equity, Preferred, Carrying Amount Tax Effect - Tax Regulatory Liabilities Deferred Tax Assets Tax Effect Tax Regulatory Liabilities Deferred Debits and Other Assets: Assets, Noncurrent [Abstract] Unrealized Loss on Marketable Securities, Net of Tax AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-Sale, Parent [Member] Accretion Asset Retirement Obligation, Accretion Expense Equity method investment, pre tax charge Equity Method Investment, Pre Tax Charge Equity Method Investment, Pre Tax Charge 2014 Debentures due 2044   Unsecured Notes Due 2044 [Member] Unsecured Notes Due 2044 [Member] 2024 Series A due 2029 2024 Series A due 2029 [Member] 2024 Series A due 2029 Senior Notes Senior Notes [Member] Netting Derivative Liability, Subject to Master Netting Arrangement, Asset Offset Seabrook Nuclear Power Plant Seabrook Nuclear Power Plant [Member] Seabrook Nuclear Power Plant [Member] Defined Contribution Plan [Table] Defined Contribution Plan [Table] Fair Value Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Fair Value [Abstract] Distribution - Water Public Utilities Property Plant And Equipment Distribution, Water Public Utilities Property Plant And Equipment Distribution, Water All Executive Categories All Executive Categories [Member] Schedule of Accumulated Deferred Income Tax Obligations Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Schedule of Benefit Obligations in Excess of Fair Value of Plan Assets Defined Benefit Plan, Plan with Projected Benefit Obligation in Excess of Plan Assets [Table Text Block] Common Stock Common Shares Common Stock, Value, Issued Right-of-use-Assets, Net Finance Lease, Right-of-Use Asset, after Accumulated Amortization Title and Position [Axis] Title and Position [Axis] Transaction and integration cost Business Combination, Integration-Related Cost, Expense Disposal group, including discontinued operation, pre-tax income Disposal Group, Including Discontinued Operation, Pre-Tax Income Disposal Group, Including Discontinued Operation, Pre-Tax Income Commitments and Contingencies (Note 13) Commitments and Contingencies 2005 Series B due 2035 Series B 2005 Notes Due 2035 [Member] Series B 2005 Notes Due 2035 [Member] Business Combination [Axis] Business Combination [Axis] Other Revenues Revenue Not from Contract with Customer, Other Loans Payable Loans Payable [Member] Schedule of Restrictions on Retained Earnings [Table] Schedule of Restrictions on Retained Earnings [Table] Schedule of Restrictions on Retained Earnings [Table] Long-Term Debt, Due Within One Year Long-Term Debt, Due Within One Year Long-Term Debt, Due Within One Year Securitized Stranded Costs Stranded Costs [Member] Shares issued (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Shares Issued in Period Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Shares Issued in Period Restricted Cash and Cash Equivalent Item [Line Items] Restricted Cash and Cash Equivalent Item [Line Items] Defined benefit plan, loss due to updated census data Defined Benefit Plan, Loss Due to Updated Census Data Defined Benefit Plan, Loss Due to Updated Census Data Interest Income Interest Income [Member] Number of electric and natural gas customers Number of Electric, Natural Gas And Water Customers Number of Electric, Natural Gas And Water Customers Ownership interest (in percent) Equity Method Investment, Ownership Percentage Yankee Gas Services Company Yankee Gas Services Company [Member] Noncontrolling Interest [Table] Noncontrolling Interest [Table] Short-term Debt [Line Items] Short-Term Debt [Line Items] Post-65 Plan Post-65 Plan [Member] Post-65 Plan [Member] Eversource - Cost of Natural Gas Fuel Power Costs Fuel power costs included in Fuel, Purchased and Net Interchange line item on the income statement PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount FERC MISO Complaints FERC MISO Complaints [Member] FERC MISO Complaints Assumed Rate of Return (in percent) Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage Greater than ten years Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10 North East Offshore and Revolution Wind, LLC North East Offshore and Revolution Wind, LLC [Member] North East Offshore and Revolution Wind, LLC SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES SEC Schedule, 12-09, Schedule of Valuation and Qualifying Accounts Disclosure [Text Block] Remaining amortization (in years) Regulatory Asset, Remaining Amortization Period Regulatory Asset, Remaining Amortization Period Revenue from Contract with Customer [Abstract] Revenue from Contract with Customer [Abstract] Scenario [Axis] Scenario [Axis] Purchase Accounting Adjustment Deferred Tax Asset, Purchase Accounting Cost of Removal Expenditures Regulatory Assets, Removal Costs (Income) Regulatory Assets, Removal Costs (Income) Schedule of Unrecognized Tax Benefits Roll Forward Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block] Wholesale Transmission Revenues Wholesale Transmission Revenue [Member] Wholesale Transmission Revenue [Member] Number of capacity contracts Unrecorded Unconditional Purchase Obligation, Number of Capacity Contracts Unrecorded Unconditional Purchase Obligation, Number of Capacity Contracts Actuarial Loss/(Gain) Reclassified from Held for Sale Gain (Loss) Reclassified From Held for Sale Gain (Loss) Reclassified From Held for Sale Other Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment Amortization of RRB Principal (included in Amortization of Regulatory Assets/(Liabilities), Net) Amortization of Regulatory Asset Tax effect on total share-based payments (in percentage) Effective Tax Rate Reconciliation, Percent, Tax Effect on Share-Based Payments Effective Tax Rate Reconciliation, Percent, Tax Effect on Share-Based Payments Schedule of Other Retirement Benefits Schedule of Deferred Compensation Arrangement with Individual, Excluding Share-Based Payments and Postretirement Benefits by Title of Individual and Type of Deferred Compensation [Table Text Block] Other Long-Term Assets Disposal Group, Including Discontinued Operation, Other Assets, Noncurrent Connecticut, Massachusetts and New Hampshire Connecticut, Massachusetts and New Hampshire [Member] Connecticut, Massachusetts and New Hampshire [Member] Changes in Funded Status of Pension, SERP and PBOP Benefit Plans Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax Amortization of Regulatory Assets/(Liabilities), Net Amortization Of Regulatory Asset (Liabilities) Amortization Of Regulatory Asset (Liabilities) Issuance of Common Shares, Net of Issuance Costs Proceeds from Issuance of Common Stock Environmental Site for Which a Range is Too Early to Determine Environmental Site for Which a Range is Too Early to Determine [Member] Environmental Site for Which a Range is Too Early to Determine [Member] 2030 Defined Benefit Plan, Expected Future Benefit Payment, Year Five Pre-tax benefit to earnings, recoupment Pre-Tax Benefit to Earnings, Recoupment Pre-Tax Benefit to Earnings, Recoupment All Individuals All Individuals [Member] Long-term Debt, Type [Domain] Long-Term Debt, Type [Domain] Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Hardship Accounts Hardship Accounts [Member] Hardship Accounts Investments in Property, Plant and Equipment Payments to Acquire Property, Plant, and Equipment Name Forgone Recovery, Individual Name 2029 Unrecorded Unconditional Purchase Obligation, to be Paid, Year Four Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested [Member] Unrecovered storm costs Unrecovered Storm Costs Unrecovered Storm Costs Reclassification out of Accumulated Other Comprehensive Income Reclassification out of Accumulated Other Comprehensive Income [Member] Total Assets Before 401 Total Assets Before 401 (h) [Member] Total Assets Before 401 (h) [Member] Disposal Group Classification [Axis] Disposal Group Classification [Axis] Weighted average interest rate (in percent) Debt, Weighted Average Interest Rate SERP Supplemental Pension Program (SERP) [Member] Supplemental Pension Program (SERP) Peaker CfDs Peaker CfD Expense Incurred Regulatory Over/(Under) Recoveries, Net Regulatory (Under)/Over Recoveries, Net Increase (Decrease) in Regulatory Assets and Liabilities Equity Method Investee Equity Method Investee [Member] Amortized Cost Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract] Equity Securities Defined Benefit Plan, Equity Securities [Member] Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Cash Paid/(Received) During the Year for: Interest Paid, Excluding Capitalized Interest, Operating Activities [Abstract] Interest Paid, Excluding Capitalized Interest, Operating Activities [Abstract] Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Geographical [Axis] Geographical [Axis] Lessee, Lease, Description [Line Items] Lessee, Lease, Description [Line Items] Other Current Assets and Liabilities, Net Other Current Assets and Liabilities, Net Increase (Decrease) in Other Operating Assets and Liabilities, Net Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Connecticut CONNECTICUT Changes in Funded Status of SERP Benefit Plan Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax and Reclassification Adjustment, Attributable to Parent Purchased Power, Purchased Natural Gas and Transmission Purchased Power and Transmission Utilities Operating Expense, Purchased Power, Purchased Natural Gas, Purchased Transmission, And Fuel Used Utilities Operating Expense, Purchased Power, Purchased Natural Gas, Purchased Transmission, And Fuel Used SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items] SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items] 2030 Rate Reduction Bonds, Principal And Interest Payments To Be Paid, Year Five Rate Reduction Bonds, Principal And Interest Payments To Be Paid, Year Five Forecast Forecast [Member] Composite depreciation rate for plant in service (in percent) Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Regulatory Assets Disposal Group, Including Discontinued Operation, Regulatory Assets Disposal Group, Including Discontinued Operation, Regulatory Assets Title of 12(b) Security Title of 12(b) Security Lessee, Lease, Description [Table] Lessee, Lease, Description [Table] Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] Cash Paid During the Year for: Income Taxes Paid, Net [Abstract] Earnings Per Share [Abstract] Earnings Per Share [Abstract] Pension, SERP and PBOP Income, Net Pension, SERP and PBOP Income, Net Pension and Other Postretirement Benefits Cost (Reversal of Cost) Cash Dividends Received from Subsidiaries SEC Schedule, 12-04, Cash Dividends Paid to Registrant, Consolidated Subsidiaries 2030 Lessee, Operating Lease, Liability, to be Paid, Year Five Other Income, Net Other Income/(Loss), Net Nonoperating Income (Expense) 2022 Debentures due 2052 4.550% Notes Due 2052 [Member] 4.550% Notes Due 2052 2023 Series X due 2033 5.350% Series X Due 2033 [Member] 5.350% Series X Due 2033 Energy Relief Fund Energy Relief Fund - Merrimack Valley Programs [Member] Energy Relief Fund - Merrimack Valley Programs Tax Credit Tax Credit Carryforward, Amount Sale of Water Unregulated Business and Water Acquisition, net Goodwill disposed of Goodwill, Written off Related to Sale of Business Unit 2005 Series M due 2035 Series M Notes Due 2035 [Member] Series M Notes Due 2035 [Member] Uncommitted Lease Area Uncommitted Lease Area [Member] Uncommitted Lease Area Short-term Debt, Type [Axis] Short-Term Debt, Type [Axis] Obligations to Third Party Suppliers Accounts Payable, Other, Current Actuarial Loss/(Gain) Arising During the Year Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax Weighted Average Number of Shares Outstanding, Diluted, Adjustment [Abstract] Weighted Average Number of Shares Outstanding, Diluted, Adjustment [Abstract] NSTAR Gas Series R First Mortgage Bonds NSTAR Gas Series R First Mortgage Bonds [Member] NSTAR Gas Series R First Mortgage Bonds Public utilities, approved rate, requirement of revenue Public Utilities, Approved Rate, Requirement Of Revenue Public Utilities, Approved Rate, Requirement Of Revenue Thereafter Finance Lease, Liability, to be Paid, after Year Five Mutual Funds and Equities Mutual Funds [Member] Represents investments in mutual and exchange traded funds Actuarial (Loss)/Gain Reclassified as Held for Sale Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassified as Held for Sale Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassified as Held for Sale Gain (loss) on deferred regulatory costs Derivative Instruments Gain (Loss) Recognized In Regulatory Asset Liability Derivative Instruments Gain (Loss) Recognized In Regulatory Asset Liability Award Timing Disclosures [Line Items] Operating Loss Carryforwards [Line Items] Operating Loss Carryforwards [Line Items] Schedule of Change in Asset Retirement Obligation Schedule of Change in Asset Retirement Obligation [Table Text Block] Related Parties Related Party [Policy Text Block] Related Party [Policy Text Block] Service Cost Defined Benefit Plan, Service Cost Charitable contribution Charitable Contribution Amount of future tax deductions arising from contributions in excess of statutory limitations in historical filings, and which can only be realized if sufficient tax-basis income is generated in future periods to enable deductions to be taken and providing tax laws continue to allow such deductions. Beginning balance (in shares) Ending balance (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested and Vested, Number Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested and Vested, Number Recoveries Collected Accounts Receivable, Allowance for Credit Loss, Recovery COMMON SHARES COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS Equity [Text Block] State Deferred State and Local Income Tax Expense (Benefit) Transmission - Electric Public Utilities, Property, Plant and Equipment, Transmission 2027 Rate Reduction Bonds, Principal And Interest Payments To Be Paid, Year Two Rate Reduction Bonds, Principal And Interest Payments To Be Paid, Year Two Net Income/(Loss) Net Income/(Loss) Net Income (Loss) Attributable to Parent Liabilities, Noncurrent [Abstract] Liabilities, Noncurrent [Abstract] Property, Plant and Equipment, Net Total Property, Plant and Equipment, Net Public Utilities, Property, Plant and Equipment, Net Summary of Accounting Policies [Line Items] Summary of Accounting Policies [Line Items] [Line Items] for Summary of Accounting Policies [Table] Construction in Progress Construction in Progress [Member] Summary of Income Tax Examinations Summary of Income Tax Examinations [Table Text Block] Charitable contributions Payments For Charitable Contributions, Related Parties Payments For Charitable Contributions, Related Parties Summary of Reconciliation Between Income Tax Expense and Expected Tax Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Long-Term Liabilities Held for Sale Liabilities Held-for-sale, Not Part of Disposal Group, Noncurrent Liabilities Held-for-sale, Not Part of Disposal Group, Noncurrent Other Effective Income Tax Rate Reconciliation, Other Adjustments, Percent Deductions SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction Cost of Removal Cost Of Removal [Member] The regulated companies currently recover amounts in rates for future costs of removal of plant assets over the lives of the assets. Restrictions on Cash and Cash Equivalents [Table] Restrictions on Cash and Cash Equivalents [Table] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Alternative Revenue Programs Revenue Not from Contract with Customer Preferred stock, shares authorized (in shares) Preferred Stock, Shares Authorized Deferred Tax Assets: Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits [Abstract] Accrued Taxes Taxes Payable Adoption Date Trading Arrangement Adoption Date Other inventory, capitalized costs, gross Other Inventory, Capitalized Costs, Gross Consolidations Eliminations Consolidation, Eliminations [Member] Rate Reduction Bonds Rate Reduction Bonds [Member] Rate Reduction Bonds [Member] Operating Income Operating Income (Loss) Operating Income (Loss) Line of Credit Line of Credit [Member] Retained Earnings Retained Earnings Retained Earnings (Accumulated Deficit) Cash Paid for Amounts Included in the Measurement of Lease Liabilities: Cash Flow, Lessee [Abstract] Cash Flow, Lessee [Abstract] Rate Credit Rate Credit [Member] Rate Credit Unusual or Infrequent Item, or Both [Axis] Unusual or Infrequent Item, or Both [Axis] Summary of Share Transactions Share-Based Payment Arrangement, Cost by Plan [Table Text Block] Actuarial (Loss)/Gain Reclassified as Held for Sale Gain (Loss) Reclassified as Held for Sale Gain (Loss) Reclassified as Held for Sale Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] Equity in Earnings of Unconsolidated Affiliates Equity in Earnings [Member] Equity in Earnings [Member] 2026 Recorded Unconditional Purchase Obligation, to be Paid, Year One Health care trend rate Defined Benefit Plan, Health Care Trend Rate Defined Benefit Plan, Health Care Trend Rate Class of Stock [Axis] Class of Stock [Axis] Qualified Cash Flow Hedging Instruments Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] Subsequent Event Type [Domain] Subsequent Event Type [Domain] 2025 Debentures due 2035 5.200% Notes Due 2035 [Member] 5.200% Notes Due 2035 Storm costs recovered Storm Costs Recovered in Base Rates Storm Costs Recovered in Base Rates Regulatory Tracking Mechanisms Regulatory Tracker Deferrals Regulatory Liabilities [Member] Regulatory tracker deferrals are approved rate mechanisms that allow utilities to recover costs in specific business segments through reconcilable tracking mechanisms that are reviewed at least annually by the applicable regulatory commission. Regulatory tracker deferrals are recorded as regulatory assets if unrecovered costs are in excess of collections and are recorded as regulatory liabilities if collections are in excess of costs. Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table [Member] Current Liabilities Held for Sale Disposal Group, Including Discontinued Operation, Liabilities, Current Other Deferred Tax Liabilities, Other Retirement Plan Type [Axis] Retirement Plan Type [Axis] Other Income, Net Other Nonoperating Income (Expense) Statement [Table] Statement [Table] 2028 Recorded Unconditional Purchase Obligation, to be Paid, Year Three Actual Return on Plan Assets Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss) Adjustments to Reconcile Net Income/(Loss) to Net Cash Flows Provided by Operating Activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] Deferred Income Taxes Total Deferred Deferred Income Tax Expense (Benefit) Lapse of Statute of Limitations Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations Net Regulatory Assets [Abstract] Net Regulatory Assets [Abstract] Financing Activities: Financing Activities: Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] 2028 Rate Reduction Bonds, Principal And Interest Payments To Be Paid, Year Three Rate Reduction Bonds, Principal And Interest Payments To Be Paid, Year Three 2017 Debentures due 2027 Unsecured Notes Due 2027 [Member] Unsecured Notes Due 2027 [Member] Energy Efficiency Programs Energy Efficiency Programs These costs are in accordance with energy efficiency and conservation program guidelines established by regulators. Long-Term Finance Lease, Liability, Noncurrent Natural Gas Distribution Natural Gas Distribution Natural Gas Distribution [Member] Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract] Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract] 2019 Debentures due 2029 Unsecured Notes Due 2029 [Member] Unsecured Notes Due 2029 [Member] Assets Held for Sale, Current Assets Held for Sale, Current [Member] Assets Held for Sale, Current Massachusetts MASSACHUSETTS All Adjustments to Compensation All Adjustments to Compensation [Member] Net Amount Recorded as a Derivative Derivative Liability, Subject to Master Netting Arrangement, before Offset of Collateral Amendment Flag Amendment Flag Future Income Tax Benefit Share-Based Payment Arrangement, Expense, Tax Benefit EGMA EGMA [Member] EGMA Shares granted in incentive plan (up to) (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized PBOP Other Postretirement Benefits Plan [Member] Schedule of Allocation of Plan Assets Schedule of Allocation of Plan Assets [Table Text Block] Condensed Income Statements, Captions [Line Items] Condensed Income Statements, Captions [Line Items] Reduce costs of hardship protection measures charged to retail customers (percent) Reduce Costs of Hardship Protection Measures Charged to Retail Customers, Percent Reduce Costs of Hardship Protection Measures Charged to Retail Customers, Percent Marketable Securities Recorded at Fair Value Fair Value Heirarchy [Table Text Block] Termination Date Trading Arrangement Termination Date Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Capitalization: Long-Term Debt, Excluding Current Maturities [Abstract] Other Long-Term Liabilities Disposal Group, Including Discontinued Operation, Other Liabilities, Noncurrent Receivable [Domain] Receivable [Domain] Operating Leases Operating Lease, Weighted Average Discount Rate, Percent Aquarion Aquarion [Member] Aquarion [Member] Increase in valuation allowance Valuation Allowance, Deferred Tax Asset, Increase, Amount Valuation Allowance, Deferred Tax Asset, Increase, Amount North East Offshore and South Fork Class B Member, LLC North East Offshore and South Fork Class B Member, LLC [Member] North East Offshore and South Fork Class B Member, LLC Basic (in shares) Weighted Average Number of Shares Outstanding, Basic Benefits Paid - Lump Sum Benefits Paid - Lump Sum Defined Benefit Plan Benefits Paid Lump Sum The amount of benefit plan payments made in a lump sum to participants. Environmental Sites for Which a Range of Loss Exists Environmental Sites for Which a Range of Loss Exists [Member] Environmental Sites for Which a Range of Loss Exists [Member] New Hampshire NEW HAMPSHIRE Components of Basic and Diluted EPS Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Payments for Offshore Wind Contingent Liability Payment for Contingent Consideration Liability, Investing Activities Disposal group, including discontinues operation, debt Disposal Group, Including Discontinued Operation, Debt Disposal Group, Including Discontinued Operation, Debt Segment Reporting [Abstract] Segment Reporting [Abstract] 2022 Debentures due 2052 4.950% Notes Due 2052 [Member] 4.950% Notes Due 2052 Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP Deferred Portion of Non-Service Income [Member] Deferred Portion of Non-Service Income Unbilled Revenues Receivable from Customer in Brokerage Defined Contribution Plan, 401K Defined Contribution Plan, 401K [Member] Defined Contribution Plan, 401K [Member] Prior Service Cost Arising During the Year Prior Service Cost (Credit) Arising During Period, Regulatory Asset Prior Service Cost (Credit) Arising During Period, Regulatory Asset Debt Disclosure [Abstract] Debt Disclosure [Abstract] Other Income, Net: Nonoperating Income (Expense) [Abstract] Defined Benefit Plan, Plan Assets, Category [Axis] Defined Benefit Plan, Plan Assets, Category [Axis] Scenario [Domain] Scenario [Domain] Actuarial (Loss)/Gain Reclassified as Net Periodic Benefit (Expense)/Income Losses Reclassifed From RegAsset PreTax he net gain (loss) previously recognized in regulatory assets that is a reclassification adjustment of other comprehensive income as a result of being recognized as a component of net periodic benefit cost for the period. 2023 Debentures due 2028 5.600% Notes Due 2028 [Member] 5.600% Notes Due 2028 Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] Write-Offs Accounts Receivable, Allowance for Credit Loss, Writeoff Delayed recovery of capital pipeline investments Public Utilities, Delayed Recovery of Capital Pipeline Investments Public Utilities, Delayed Recovery of Capital Pipeline Investments Interest expense on uncertain tax positions Unrecognized Tax Benefits, Interest on Income Taxes Expense Utility     Public Utilities, Property, Plant and Equipment, Accumulated Depreciation, Electric, Natural Gas and Water Utility Public Utilities, Property, Plant and Equipment, Accumulated Depreciation, Electric, Natural Gas and Water Utility Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Consolidated Entities [Axis] Consolidated Entities [Axis] Public utilities, approved equity capital structure, percentage Public Utilities, Approved Equity Capital Structure, Percentage Par value of Common Shares (in dollars per share) Per share par value (in dollars per share) Common Stock, Par or Stated Value Per Share GSEP Investments GSEP Investments [Member] GSEP Investments Derivative Instruments and Hedging Activities Disclosures [Line Items] Derivative Instruments and Hedging Activities Disclosures [Line Items] Distribution - Water Water Assets Average Useful Life Water Assets Average Useful Life Capital Contributions to Subsidiaries Capital Contributions To Subsidiaries 2031 - 2035 Defined Benefit Plan, Expected Future Benefit Payment, after Year Five for Next Five Years Water assets held for sale Water Assets Held for Sale Water Assets Held for Sale Public Utilities, Regulatory Proceeding [Axis] Public Utilities, Regulatory Proceeding [Axis] Receivables, Net Disposal Group, Including Discontinued Operation, Accounts, Notes and Loans Receivable, Net Various Eversource subsidiaries Various Entities [Member] Various Entities Guarantor Obligations, Nature [Axis] Guarantor Obligations, Nature [Axis] Operating Cash Flows from Finance Leases Finance Lease, Interest Payment on Liability Less: Accrued SERP - current portion Liability, Defined Benefit Plan, Current Total Regulatory Assets Securitized Stranded Cost (included in Regulatory Assets) Regulatory Asset Pension, SERP and PBOP Non-Service Income Components, Net of Deferred Portion Non-Service Cost Benefits [Member] Non-Service Cost Benefits [Member] 2010 Debentures due 2040 Unsecured Notes Due 2040 [Member] Unsecured Notes Due 2040 [Member] Weighted-Average Discount Rate (Percentage): Lessee, Lease, Weighted Average Discount Rate [Abstract] Lessee, Lease, Weighted Average Discount Rate [Abstract] Increase of liability as a result of change in discount rate Defined Benefit Plan, Increase of Liability As A Result of Change in Discount Rate Defined Benefit Plan, Increase of Liability As A Result of Change in Discount Rate 2021 Debentures due 2051 3.100% Notes Due 2051 [Member] 3.100% Notes Due 2051 Netting Derivative Asset, Subject to Master Netting Arrangement, Liability Offset Insider Trading Arrangements [Line Items] Regulatory Liabilities Less:  Current Portion Regulatory Liability, Current Loss on Offshore Wind Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Percent Operating Leases: Lessee, Lease, Operating Lease [Abstract] Lessee, Lease, Operating Lease [Abstract] 2030 Finance Lease, Liability, to be Paid, Year Five Common Shares Common Stock, Value, Outstanding Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Gross Increases - Current Year Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions Debt Instrument, Term Extended Debt Instrument, Term Extended Debt Instrument, Term Extended Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Repayment of Rate Reduction Bonds Proceeds (Payments) Of Issuance Of Rate Reduction Bonds Proceeds (Payments) Of Issuance Of Rate Reduction Bonds Transmission Support Commitments Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract] Operations and Maintenance Operations and Maintenance Other Utilities Operating Expense, Maintenance and Operations Issuance of Common Shares Stock Issued During Period, Value, New Issues Asset-Backed Debt Securities Asset-Backed Securities [Member] Consolidation Items [Axis] Consolidation Items [Axis] Counterparty Name [Axis] Counterparty Name [Axis] Regulatory Amounts: Components of Deferred Tax Liabilities [Abstract] Fair Value Total Debt Securities Debt Securities, Available-for-Sale Millstone Nuclear Power Station and Seabrook Nuclear Power Plant Millstone Nuclear Power Station And Seabrook Nuclear Power Plant [Member] Millstone Nuclear Power Station And Seabrook Nuclear Power Plant [Member] Tax Credit Carryforward, Name [Domain] Tax Credit Carryforward, Name [Domain] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Non-NEOs Non-NEOs [Member]