Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] Utility Public Utilities Property Plant And Equipment Electric And Natural Gas Utility Total Period end amount of property, plant and equipment (PPE) related to utility Weighted Average Common Shares Outstanding: Weighted Average Number of Shares Outstanding, Diluted [Abstract] Trading Arrangement: Trading Arrangement [Axis] Short-term debt, paid Short-Term Debt, Other, Average Rate Paid Maximum Maximum [Member] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Statistical Measurement [Domain] Statistical Measurement [Domain] Mutual Funds and Equities Mutual Funds [Member] Represents investments in mutual and exchange traded funds Total Accumulated Depreciation Public Utilities, Property, Plant and Equipment, Accumulated Depreciation Short-term Debt, Type [Axis] Short-Term Debt, Type [Axis] Title of 12(b) Security Title of 12(b) Security Carrying Amount Reported Value Measurement [Member] Debt Securities, Available-for-sale [Table] Debt Securities, Available-for-Sale [Table] Subsequent Event Subsequent Event [Member] Document Fiscal Year Focus Document Fiscal Year Focus Weighted average interest rate (in percent) Debt, Weighted Average Interest Rate South Fork Wind, LLC South Fork Wind LLC [Member] South Fork Wind LLC Adjustment to Compensation, Amount Adjustment to Compensation Amount Financial Instrument [Axis] Financial Instrument [Axis] NSTAR Electric and Eversource NSTAR Electric and Eversource [Member] NSTAR Electric and Eversource Segment Reporting [Abstract] Segment Reporting [Abstract] Common Stock Common Stock, Value, Issued Payments for Offshore Wind Contingent Liability Payment for contingent consideration Payment for Contingent Consideration Liability, Investing Activities Interest Expense on RRB Principal (included in Interest Expense) Interest Expense, Operating and Nonoperating Schedule of Long-Term Debt Issuance and Repayments Schedule of Long-Term Debt Instruments [Table Text Block] NSTAR Electric Company NSTAR Electric NSTAR Electric Company [Member] PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSION Retirement Benefits [Text Block] Maximum exposure (up to) Guarantor Obligations, Maximum Exposure, Undiscounted Line of Credit Line of Credit [Member] Restatement Determination Date Restatement Determination Date Expected Return on Plan Assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets EGMA Series EGMA Series [Member] EGMA Series Energy Relief Fund - Merrimack Valley Programs Energy Relief Fund - Merrimack Valley Programs [Member] Energy Relief Fund - Merrimack Valley Programs Beginning balance Ending balance Accounts Receivable, Allowance for Credit Loss Schedule of Property, Plant, and Equipment Public Utility Property, Plant, and Equipment [Table Text Block] Proceeds from Sale of Aquarion Proceeds from sale of Aquarion Proceeds from Divestiture of Businesses Regulatory Liabilities Total Long-Term Regulatory Liabilities Other Regulatory Liabilities (included in Regulatory Liabilities) Regulatory Liability, Noncurrent Interest Expense Interest Expense, Nonoperating, Adjusted Interest Expense, Nonoperating, Adjusted Amendment Flag Amendment Flag Proceeds from sale of equity method investments Proceeds from Sale of Equity Method Investments Consolidated Entities [Axis] Consolidated Entities [Axis] 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. Current Liabilities: Liabilities, Current [Abstract] Uncollectible Expense Accounts Receivable, Credit Loss Expense (Reversal) Other Revenues Revenue Not from Contract with Customer, Other Entity Common Stock, Shares Outstanding (in shares) Entity Common Stock, Shares Outstanding Commercial operation, term Commercial Operation, Term Commercial Operation, Term Disposal Group Classification [Axis] Disposal Group Classification [Axis] Pre-Tax Unrealized Losses Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax Asset-Backed Debt Securities Asset-Backed Securities [Member] Loss Contingencies [Table] Loss Contingencies [Table] Amortization Amortization Percentage of base ROE Percentage of Base ROE of Complaint Period Percentage of Base ROE of Complaint Period Other Comprehensive Income, Net of Tax: Other Comprehensive Loss, Net of Tax: Other Comprehensive Income (Loss), Net of Tax [Abstract] Consolidated Entities [Domain] Consolidated Entities [Domain] Renewable Portfolio Standards Compliance Obligations Renewable Portfolio Standards Compliance Obligation The current obligation PSNH has in order to meet renewable compliance standards. Obligations to Third Party Suppliers Accounts Payable, Other, Current Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Property, plant and equipment, net Disposal Group, Including Discontinued Operation, Property, Plant, and Equipment ROE Type [Axis] ROE Type [Axis] ROE Type Investment (Loss)/Income Investment Income (Loss) [Member] Investment Income (Loss) [Member] Property, Plant, and Equipment [Abstract] Property, Plant, and Equipment [Abstract] Entity Address, State or Province Entity Address, State or Province Public Utility, Property, Plant and Equipment [Table] Public Utility, Property, Plant and Equipment [Table] 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 REGULATORY ACCOUNTING Public Utilities Disclosure [Text Block] PEO Total Compensation Amount PEO Total Compensation Amount Par value (in dollars per share) Common Stock, Par or Stated Value Per Share Cash Flows Used for Investments in Plant Segment Reporting, Long-Lived Asset, Expenditure for Addition FERC ROE First, Second and Third Complaints FERC ROE First, Second and Third Complaints [Member] FERC ROE First, Second and Third Complaints [Member] Aquarion Aquarion [Member] Aquarion [Member] Basic (in shares) Weighted Average Number of Shares Outstanding, Basic Energy Efficiency Programs Energy Efficiency Programs These costs are in accordance with energy efficiency and conservation program guidelines established by regulators. Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Energy price Energy Price Energy Price Regulatory Assets Total Long-Term Regulatory Assets Regulatory Asset, Noncurrent Loss Contingencies [Line Items] Loss Contingencies [Line Items] Industrial Industrial [Member] Industrial [Member] Number of reportable segment Number of Reportable Segments Total Current Liabilities Liabilities, Current 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 Regulatory Liability [Axis] Regulatory Liability [Axis] Taxes Other Than Income Taxes Taxes, Miscellaneous Six to ten years Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 Other Revenues from Contracts with Customers Other Revenue Adjustments from Contracts with Customers [Member] Other Revenue Adjustments from Contracts with Customers [Member] Short-term Debt, Type [Domain] Short-Term Debt, Type [Domain] Revenues from Contracts with Customers Revenue from Contract with Customer, Including Assessed Tax Entity Address, City or Town Entity Address, City or Town Schedule of Non-Cash Investing Activities Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Amortized Cost Debt Securities, Available-for-Sale, Amortized Cost, Fiscal Year Maturity [Abstract] Repayment of Rate Reduction Bonds Repayments Of Rate Reduction Bonds Repayments Of Rate Reduction Bonds Environmental Remediation Costs Environmental Remediation Costs [Member] Environmental Remediation Costs Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] 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. Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Cash Dividends on Preferred Stock Payments of Ordinary Dividends, Preferred Stock and Preference Stock 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. Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Net Income Attributable to Common Shareholders Net Income Attributable to Common Shareholders Net Income (Loss) Available to Common Stockholders, Basic Catastrophic Storm Costs Catastrophic Storm Costs [Member] Catastrophic Storm Costs Orsted Orsted [Member] Orsted Level 2 Fair Value, Inputs, Level 2 [Member] Receivable [Domain] Receivable [Domain] Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] FERC ROE Second Complaint FERC ROE Second Complaint [Member] FERC ROE Second Complaint [Member] Maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Other Comprehensive Income, Net of Tax Other Comprehensive Income Other Comprehensive Income (Loss), Net of Tax Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] Long-Term Debt – Current Portion Long-term debt, current portion Long-Term Debt, Current Maturities Other Other Expenses Federal investment tax credits (percent) Effective Income Tax Rate Reconciliation, Tax Credit, Percent Eversource Parent Commercial Paper Program Parent Company [Member] Eversource Investment LLC, Eversource Investment Service Company LLC and South Fork Class B Member, LLC Eversource Investment Service Company, LLC and South Fork Class B Member, LLC, Eversource Investment LLC [Member] Eversource Investment Service Company, LLC and South Fork Class B Member, LLC, Eversource Investment LLC Eversource Parent Series A Junior Notes Eversource Parent Series A Junior Notes [Member] Eversource Parent Series A Junior Notes Dividends on Preferred Stock Dividends on preferred stock Dividends, Preferred Stock Subsequent Event Type [Axis] Subsequent Event Type [Axis] Qualified Cash Flow Hedging Instruments Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax Schedule of Long-term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] 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. Less:  Accumulated Depreciation Depreciation, Depletion and Amortization [Abstract] Water Distribution Eversource Water [Member] Eversource Water [Member] Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block] Litigation Case [Axis] Litigation Case [Axis] Plant additions included in accounts payable Capital Expenditures Incurred but Not yet Paid Schedule of Segment Information and Segmented Total Assets Segment Reporting [Table Text Block] Natural gas transition service transaction costs Natural Gas Transition Service Transaction Costs Natural Gas Transition Service Transaction Costs Distribution - Water Public Utilities Property Plant And Equipment Distribution, Water Public Utilities Property Plant And Equipment Distribution, Water Commercial Commercial [Member] Commercial [Member] Municipal Bonds Municipal Bonds [Member] Unsecured Debt Unsecured Debt [Member] Related Party [Axis] Related and Nonrelated Parties [Axis] Other Comprehensive Loss, Net of Tax Other Comprehensive Loss Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Schedule of Components of Regulatory Liabilities Schedule of Regulatory Liabilities [Table Text Block] Long-Term Debt Long-Term Debt Yankee Gas Series AA First Mortgage Bonds Yankee Gas Series AA First Mortgage Bonds [Member] Yankee Gas Series AA First Mortgage Bonds PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION Property, Plant, and Equipment [Text Block] Guarantor Obligations [Line Items] Guarantor Obligations [Line Items] One to five years Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five Document Period End Date Document Period End Date 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] Net Cash Flows Used in Investing Activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Equity Awards Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] North East Offshore, Revolution Wind, LLC and South Fork Wind, LLC North East Offshore, Revolution Wind, LLC [Member] North East Offshore, Revolution Wind, LLC Amount of securitized rate reduction bonds issued Debt Instrument, Face Amount Total Regulatory Assets Regulatory assets Securitized Stranded Cost (included in Regulatory Assets) Regulatory Asset COMMON SHARES COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS Equity [Text Block] Security Exchange Name Security Exchange Name Debt instrument term (in years) Debt Instrument, Term Treasury Stock Treasury Stock, Common, Value 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. Consolidations Eliminations Consolidation, Eliminations [Member] FERC ROE Fourth Complaint FERC ROE Fourth Complaint [Member] FERC ROE Fourth Complaint [Member] Water Distribution Water Distribution Segment [Member] Water Distribution Segment Greater than ten years Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 10 Solar Public Utilities, Property, Plant and Equipment, Generation or Processing Purchases of Marketable Securities Payments to Acquire Marketable Securities Loss on Offshore Wind Loss on Offshore Wind Equity Method Investment, Other-than-Temporary Impairment Accumulated Other Comprehensive Loss Accumulated Other Comprehensive Income Accumulated Other Comprehensive Income (Loss), Net of Tax Entity Shell Company Entity Shell Company Consolidation Items [Domain] Consolidation Items [Domain] Accrued Interest Interest Payable, Current Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] EARNINGS PER SHARE Earnings Per Share [Text Block] Name Outstanding Recovery, Individual Name Earnings Per Share [Abstract] Earnings Per Share [Abstract] Proceeds from Sales of Marketable Securities Proceeds from Sale and Maturity of Marketable Securities Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] Document Fiscal Period Focus Document Fiscal Period Focus Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] Trading Symbol Trading Symbol Geographical [Domain] Geographical [Domain] Investments in Property, Plant and Equipment Payments to Acquire Property, Plant, and Equipment 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] Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Company Selected Measure Name Company Selected Measure Name Schedule of Reconciliation of Cash Balances to Cash and Restricted Cash Restrictions on Cash and Cash Equivalents [Table Text Block] Weighted Average Number of Shares Outstanding, Diluted, Adjustment [Abstract] Weighted Average Number of Shares Outstanding, Diluted, Adjustment [Abstract] Pension, SERP and PBOP Income, Net Pension, SERP, and PBOP Income, Net Pension and Other Postretirement Benefits Cost (Reversal of Cost) Schedule of Regulatory Assets [Table] Regulated Operation, Regulatory Asset [Table] Electric Distribution Electric Distribution Eversource Electric Distribution [Member] Eversource Electric Distribution [Member] AFUDC Equity AFUDC Equity [Member] AFUDC Equity [Member] Defined Benefit Plans Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Condensed Income Statement [Table] Condensed Income Statement [Table] Credit Facility [Domain] Credit Facility [Domain] Asset Class [Domain] Asset Class [Domain] Operating Activities: Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Compensation Amount Outstanding Recovery Compensation Amount Individual: Individual [Axis] Diluted (in shares) Diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Junior Notes Junior Notes [Member] Accounts, Notes, Loans and Financing Receivable [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Dividends on Common Shares (in dollars per share) Common Stock, Dividends, Per Share, Cash Paid Entity Emerging Growth Company Entity Emerging Growth Company Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] Income Taxes, Net Deferred Income Tax Charge [Member] Accrued SERP and PBOP Derivative Liabilities Liability, Defined Benefit Plan, Noncurrent 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] Disposal Group Name [Domain] Disposal Group Name [Domain] Line of Credit Facility [Table] Line of Credit Facility [Table] Underlying Security Market Price Change Underlying Security Market Price Change, Percent Pre-tax income Income (Loss) from Individually Significant Component Disposed of or Held-for-Sale, Excluding Discontinued Operations, before Income Tax Capital Contributions from Eversource Parent Capital Contributions from Eversource Parent Noncontrolling Interest, Increase In Contributions From Parent Noncontrolling Interest, Increase In Contributions From Parent Commercial Paper Commercial Paper [Member] DERIVATIVE INSTRUMENTS Derivative Instruments and Hedging Activities Disclosure [Text Block] Regulatory Asset [Axis] Regulatory Asset [Axis] Fair value of guarantees Guarantor Obligations, Current Carrying Value Equity method investment, pre tax charge Equity Method Investment, Pre Tax Charge Equity Method Investment, Pre Tax Charge Long-Term Derivative Liabilities Derivative Liability, Subject to Master Netting Arrangement, before Offset Total Deferred Debits and Other Assets Assets, Noncurrent, Other than Noncurrent Investments and Property, Plant and Equipment Condensed Balance Sheet Statement [Table] Condensed Balance Sheet Statement [Table] Revenue from Contract with Customer [Abstract] Revenue from Contract with Customer [Abstract] Gains from changes in fair value Net Realized/Unrealized Gains Included in Regulatory Assets and 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 Other Current Assets and Liabilities, Net Increase (Decrease) in Other Operating Assets and Liabilities, Net Award Timing Predetermined Award Timing Predetermined [Flag] Restricted cash, current Restricted Cash, Current Summary of Accounting Policies [Table] Summary of Accounting Policies [Table] Summary of Accounting Policies [Table] Treasury Stock Treasury Stock, Common [Member] Eversource Gas Company of Massachusetts Eversource Gas Company of Massachusetts [Member] Eversource Gas Company of Massachusetts Debt Securities, Available-for-sale [Line Items] Debt Securities, Available-for-Sale [Line Items] Property, Plant and Equipment, Net Total Property, Plant and Equipment, Net Public Utilities, Property, Plant and Equipment, Net Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Level 1 Fair Value, Inputs, Level 1 [Member] Unbilled Revenues Receivable from Customer in Brokerage Incentive Cap Incentive Cap [Member] Incentive Cap Amount of regulatory costs not yet approved Amount of Regulatory Costs Not yet Approved Original ROE Original ROE [Member] Original ROE Fair Value Measurements Fair Value of Financial Instruments, Policy [Policy Text Block] Tax Equity Tax Equity [Member] Tax Equity All Executive Categories All Executive Categories [Member] U.S. Government Issued Debt Securities (Agency and Treasury) US Government Debt Securities [Member] Regulated Operations [Abstract] Regulated Operations [Abstract] Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Schedule of Components of Net Periodic Benefit Expense/(Income) Schedule of Net Benefit Costs [Table Text Block] Other Regulatory Assets Other Regulatory Assets [Member] Represents various remaining other regulatory assets. Depreciation Depreciation Issuance of Treasury Shares (in shares) Stock Issued During Period, Shares, Treasury Stock Reissued Guarantor Obligations, Nature [Axis] Guarantor Obligations, Nature [Axis] Less than one year Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year One Taxes Receivable/Accrued, Net Increase (Decrease) in Income Taxes Receivable Schedule of Components of Basic and Diluted Earnings Per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Debt Disclosure [Abstract] Debt Disclosure [Abstract] Noncontrolling Interest [Line Items] Noncontrolling Interest [Line Items] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Schedule of Gross Tax Receipts [Table] Schedule of Gross Tax Receipts [Table] Schedule of Gross Tax Receipts [Table] Amortization Amortization, Including Amortization Of Regulatory Asset (Liability) Amortization, Including Amortization Of Regulatory Asset (Liability) SEGMENT INFORMATION Segment Reporting [Text Block] MARKETABLE SECURITIES Investment in Debt and Equity Securities and Other Trading Assets [Text Block] Amount outstanding under line of credit Long-Term Line of Credit Minimum Minimum [Member] Cash Dividends on Common Shares Cash Dividends on Common Stock Payments of Ordinary Dividends, Common Stock Expiration Date Trading Arrangement Expiration Date Marketable securities Investments, Fair Value Disclosure Equity method investment, remaining purchase price paid Equity Method Investment, Remaining Purchase Price Paid Equity Method Investment, Remaining Purchase Price Paid Postemployment Benefits [Abstract] Postemployment Benefits [Abstract] Schedule of Operating Revenues Disaggregated by Revenue Source Disaggregation of Revenue [Table Text Block] Weighted Average Common Shares Outstanding: Weighted Average Number of Shares Outstanding Reconciliation [Abstract] Restricted cash Restricted Cash Restricted Cash and Cash Equivalent Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Approved cost recovery amount Regulatory Assets, Approved Cost Recovery Amount Regulatory Assets, Approved Cost Recovery Amount 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] Nonrelated Party Nonrelated Party [Member] Disposal Group, Including Discontinued Operations [Line Items] Disposal Group, Including Discontinued Operations [Line Items] Effective income tax rate reconciliation, change in enacted tax rate, amount Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount Loss contingency, estimate of possible earnings impact Loss Contingency, Estimate of Possible Loss Dividends on Common Stock Dividends, Common Stock Total Net Periodic Benefit Plan Income Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Capital Stock Expense Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Issuance of Common Shares, Net of Issuance Costs Proceeds from Issuance of Common Stock Authorized (in shares) Common Stock, Shares Authorized NSTAR Electric Debentures NSTAR Electric Debentures 5.20% [Member] NSTAR Electric Debentures 5.20% Receivables and Unbilled Revenues, Net Receivables and Unbilled Revenues, Net Increase (Decrease) in Accounts and Other Receivables Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Sale of stock, number of shares issued in transaction (in shares) Sale of Stock, Number of Shares Issued in Transaction Period of complaint Loss Contingency, Period Of Complaint Loss Contingency, Period Of Complaint Number of wind projects Number Of Wind Projects Number Of Wind Projects Greater than ten years Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10 Exercise Price Award Exercise Price Investing Activities: Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] Long-Term Incentive Plan Activity Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures Schedule of Equity Method Investments [Line Items] Schedule of Equity Method Investments [Line Items] Segment Reporting [Line Items] Segment Reporting [Line Items] Schedule of Environmental Loss Contingencies by Site Schedule of Environmental Loss Contingencies by Site [Table Text Block] Schedule of Other Taxes Schedule of Gross Earnings Taxes [Table Text Block] Schedule of Gross Earnings Taxes [Table Text Block] Document Quarterly Report Document Quarterly Report Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] Percentage of ROE for any incentive Loss Contingency, Percentage of ROE for Any Incentive Project Loss Contingency, Percentage of ROE for Any Incentive Project 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] Segments [Domain] Segments [Domain] Purchased Power, Purchased Natural Gas and Transmission Purchased Power and Transmission Utilities Operating Expense, Purchased Power, Purchased Transmission, And Fuel Used Utilities Operating Expense, Purchased Power, Purchased Transmission, And Fuel Used SHORT-TERM AND LONG-TERM DEBT Debt Disclosure [Text Block] CYAPC and YAEC CYAPC and YAEC [Member] Retirement of Long-Term Debt Retirement of Long-Term Debt Long-term debt, repaid Repayments of Long-Term Debt 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. Disposal Group Classification [Domain] Disposal Group Classification [Domain] South Fork Class B Member, LLC South Fork Class B Member, LLC [Member] South Fork Class B Member, LLC Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] MGP Sites MGP Site accrual [Member] Portion of environmental liability associated with MGP sites Equity Component [Domain] Equity Component [Domain] PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount Benefit Costs Benefit Costs Benefit Costs [Member] Performance Guarantee Performance Guarantee [Member] Fair Value Debt Securities, Available-for-Sale, Fair Value, Fiscal Year Maturity [Abstract] Sale of stock, consideration received on transaction Sale of Stock, Consideration Received on Transaction Adoption Date Trading Arrangement Adoption Date Site Contingency [Table] Site Contingency [Table] Purchase price Disposal Group, Including Discontinued Operation, Consideration Interest Rate (in percent) Debt Instrument, Interest Rate, Stated Percentage Counterparty Name [Domain] Counterparty Name [Domain] Common Shareholders' Equity Beginning balance Ending balance Common Shareholders' Equity Equity, Attributable to Parent Other Income, Net Nonoperating Income (Expense) Disposed of by Sale Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] Settlement Loss Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement Purchased Power, Purchased Natural Gas and Transmission, Other Taxes and Energy Efficiency Utilities Operating Expense, Other Available-for-sale equity securities Equity Securities, FV-NI, Current ASSETS Assets [Abstract] Title Trading Arrangement, Individual Title Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Construction-related purchase agreements with third-party contractors Purchase Guarantee [Member] Purchase Guarantee Amortized Cost Debt Securities, Available-for-Sale, Amortized Cost Accounting Policies [Abstract] Accounting Policies [Abstract] Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Environmental Remediation Site [Axis] Environmental Remediation Site [Axis] Regulatory costs Deferred Regulatory Costs Deferred Regulatory Costs Eversource Parent Eversource Parent [Member] Eversource Parent 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] Insider Trading Policies and Procedures [Line Items] Other Financing Activities Proceeds from (Payment for) Other Financing Activity Allowance for uncollectible accounts Accounts Receivable, Allowance for Credit Loss, Current Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Schedule of Gross Tax Receipts [Line Items] Schedule of Gross Tax Receipts [Line Items] [Line Items] for Schedule of Gross Tax Receipts [Table] Deferred Income Taxes Deferred Income Tax Expense (Benefit) Regulatory Assets Less:  Current Portion Regulatory Asset, Current Escrow deposits related to sale of business Escrow Deposits Related To Sale Of Business Escrow Deposits Related To Sale Of Business 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 Repayments Repayments Repayments of Debt Recovery amount collected through base rates Regulatory Asset, Storm Cost Recovery Collected Through Base Rates Regulatory Asset, Storm Cost Recovery Collected Through Base Rates Letters of Credit Letter of Credit [Member] NSTAR Electric Debentures NSTAR Electric Debentures [Member] NSTAR Electric Debentures 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 Rate Reduction Bonds Rate Reduction Bonds - Long-Term Portion Rate Reduction Bonds Rate Reduction Bonds COMMITMENTS AND CONTINGENCIES Commitments and Contingencies Disclosure [Text Block] Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] FERC ROE Complaints FERC ROE Complaints [Member] FERC ROE Complaints [Member] Antidilutive share awards excluded from the EPS computation (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Gross receipts taxes Excise and Sales Taxes Entity Central Index Key Entity Central Index Key Weighted Average Weighted Average [Member] Common Shares Common Stock, Value, Outstanding Regulatory Liabilities [Line Items] Regulatory Liability [Line Items] Notes Payable to Eversource Parent Notes payable to Eversource parent Notes Payable, Current All Adjustments to Compensation All Adjustments to Compensation [Member] Other Other Segment Reporting, Reconciling Item, Corporate Nonsegment [Member] Schedule of Guarantor Obligations [Table] Guarantor Obligation [Table] Equity [Abstract] Equity [Abstract] 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] Other Taxes Income Tax, Policy [Policy Text Block] Net Cash Flows Provided by Operating Activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Funding and indemnification obligations of North East Offshore LLC Indemnification Agreement [Member] OCI Before Reclassifications Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Income Statement [Abstract] Income Statement [Abstract] Common Shareholders' Equity: Equity, Attributable to Parent [Abstract] Document Transition Report Document Transition Report Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Transaction expense Disposal Group, Transaction Expense Disposal Group, Transaction Expense Investment, Name [Axis] Investment, Name [Axis] Operating Expenses: Operating Expenses [Abstract] Power Purchase Guarantee Power Purchase Guarantee [Member] Power Purchase Guarantee Eliminations Eliminations Intersegment Eliminations [Member] Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] Eversource Investment LLC Eversource Investment, LLC [Member] Eversource Investment, LLC [Member] FERC ROE First Complaint FERC ROE First Complaint [Member] FERC ROE First Complaint [Member] South Fork Wind And Revolution Wind South Fork Wind And Revolution Wind [Member] South Fork Wind And Revolution Wind Spread rate (in percent) Debt Instrument, Basis Spread on Variable Rate Storm costs Storm Costs Storm Costs and Expenses Storm Costs and Expenses City Area Code City Area Code Accumulated Other Comprehensive Loss Accumulated Other Comprehensive Income AOCI Attributable to Parent [Member] Document Information [Table] Document Information [Table] All Individuals All Individuals [Member] Previous Incentive Cap Previous Incentive Cap [Member] Previous Incentive Cap Name Forgone Recovery, Individual Name Amortization of Regulatory (Liabilities)/Assets, Net Amortization of Regulatory Asset (Liabilities) Amortization of Regulatory Asset (Liabilities) Regulatory Liability [Domain] Regulatory Liability [Domain] Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Statement [Line Items] Statement [Line Items] Marketable Securities Marketable Securities, Noncurrent Total Assets Assets Assets Entity [Domain] Entity [Domain] Number of electric, natural gas and water customers Number Of Electric, Natural Gas And Water Customers Number Of Electric, Natural Gas And Water Customers Reserve Reserve balance Accrual for Environmental Loss Contingencies Deferred Credits and Other Liabilities: Other Liabilities, Noncurrent [Abstract] Eversource Parent Series B Junior Notes Eversource Parent Series B Junior Notes [Member] Eversource Parent Series B Junior Notes Employee Benefits Employee Benefits and Share-Based Compensation Prior Service Cost/(Credit) Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Operating Segments Operating Segments [Member] Changes in Funded Status of SERP Benefit Plan Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax and Reclassification Adjustment, Attributable to Parent Interest Expense Interest Expense Interest Expense, Nonoperating Pre-Tax Unrealized Gains Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax Various Eversource subsidiaries Various Entities [Member] Various Entities South Fork Wind Tax Equity South Fork Wind Tax Equity [Member] South Fork Wind Tax Equity Issuance of Common Shares (in shares) Stock Issued During Period, Shares, New Issues PEO PEO [Member] Distribution - Electric Public Utilities, Property, Plant and Equipment, Distribution Other Public Utilities, Property, Plant and Equipment, Accumulated Depreciation, Other Public Utilities, Property, Plant and Equipment, Accumulated Depreciation, Other Measurement Basis [Axis] Measurement Basis [Axis] EGMA Acquisition and Integration Costs EGMA Acquisition and Integration Costs [Member] EGMA Acquisition and Integration Costs Other Long-Term Liabilities Other Liabilities, Noncurrent Goodwill Goodwill Retirement Plan Type [Axis] Retirement Plan Type [Axis] Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Estimated of Interest Loss Contingency, Estimated Of Interest Component Loss Contingency, Estimated Of Interest Component Less than one year Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One Subsequent Event Type [Domain] Subsequent Event Type [Domain] Discontinued Operations, Disposed of by Sale Discontinued Operations, Disposed of by Sale [Member] Retained Earnings Retained Earnings [Member] Total Operating Expenses Operating Expenses Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Beginning balance (in shares) Ending balance (in shares) Common stock outstanding (in shares) Common Stock, Shares, Outstanding Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Award Timing Disclosures [Line Items] Schedule of Carrying Amounts and Estimated Fair Values of Financial Instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Diluted Earnings Per Common Share (in dollars per share) Earnings Per Share, Diluted Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Derivatives, Net [Rollforward] Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward] Entity Current Reporting Status Entity Current Reporting Status Net Cash Flows (Used in)/Provided by Financing Activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Total Shareholder Return Amount Total Shareholder Return Amount Litigation Case [Domain] Litigation Case [Domain] NSTAR Electric Debentures NSTAR Electric Debentures, 4.65% [Member] NSTAR Electric Debentures, 4.65% Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Operations and Maintenance Total Operations and Maintenance Utilities Operating Expense, Maintenance and Operations CL&P and NSTAR CL&P And NSTAR [Member] CL&P And NSTAR Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Financing Activities: Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Available Borrowing Capacity as of Line of Credit Facility, Remaining Borrowing Capacity Maximum percentage cap of ROE for incentive projects Loss Contingency, Percentage Of ROE For Any Incentive Project Loss Contingency, Percentage Of ROE For Any Incentive Project Interest Cost Defined Benefit Plan, Interest Cost Regulatory Assets [Line Items] Regulatory Asset [Line Items] Percentage of base ROE reasonably justified (in percent) Loss Contingency, Percentage Of Base ROE Reasonably Justified Loss Contingency, Percentage Of Base ROE Reasonably Justified Financial Instruments [Domain] Financial Instruments [Domain] Surety Bond Surety Bond [Member] Number of Sites Environmental Site Quantity Number of environmental sites by NU Entity in the remediation or long-term monitoring phase Derivative Assets Derivative Asset Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Underlying Securities Award Underlying Securities Amount EGMA Series G First Mortgage Bonds EGMA Series G First Mortgage Bonds [Member] EGMA Series G First Mortgage Bonds Comprehensive Income Attributable to Noncontrolling Interests Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Fair Value Estimate of Fair Value Measurement [Member] Sunrise Wind, LLC Sunrise Wind, LLC [Member] Sunrise Wind, LLC [Member] REVENUES Revenue from Contract with Customer [Text Block] Issuance of Common Shares Stock Issued During Period, Value, New Issues Base ROE percentage challenged by complainants Loss Contingency, Base ROE Percentage Challenged by Complainants Loss Contingency, Percentage of Base ROE Challenged by Complainants Write-Offs Accounts Receivable, Allowance for Credit Loss, Writeoff, Net Of Adjustments Accounts Receivable, Allowance for Credit Loss, Writeoff, Net Of Adjustments Cost sharing agreement, threshold amount Cost Sharing Agreement, Threshold Amount Cost Sharing Agreement, Threshold Amount Cash Cash Other Investing Activities Payment for (Proceeds from) Other Investing Activity Segment Reporting [Table] Segment Reporting [Table] Schedule of Equity Method Investments [Table] Equity Method Investment [Table] Contingent consideration liability Business Combination, Contingent Consideration, Liability, Current Schedule of Available-for-Sale Debt Securities Schedule of Available-for-Sale Securities Reconciliation [Table Text Block] Prepayments and Other Current Assets Prepayments and Other Current Assets Other Assets, Current Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] All Trading Arrangements All Trading Arrangements [Member] PSNH Series X First Mortgage Bonds PSNH Series X First Mortgage Bonds [Member] PSNH Series X First Mortgage Bonds Fair Value as of Beginning of Period Fair Value as of End of Period Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value Other Performance Measure, Amount Other Performance Measure, Amount Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Operating Income Operating Income Operating Income (Loss) Eversource Parent Series J Senior Notes Eversource Parent Series J Senior Notes [Member] Eversource Parent Series J Senior Notes Current Fiscal Year End Date Current Fiscal Year End Date Issuance Proceeds from Issuance of Debt Sale of Aquarion Sale of Aquarion Gain (Loss) on Disposition of Business North East Offshore, Revolution Wind, LLC, TurbineCo, LLC North East Offshore, Revolution Wind, LLC, TurbineCo, LLC [Member] North East Offshore, Revolution Wind, LLC, TurbineCo, LLC Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Interest Income Interest On Income [Member] Interest On Income Rate Reduction Bonds and Variable Interest Entity [Abstract] Rate Reduction Bonds and Variable Interest Entity [Abstract] Rate Reduction Bonds and Variable Interest Entity [Abstract] Revised ROE Revised ROE [Member] Revised ROE Summary of Accounting Policies [Line Items] Summary of Accounting Policies [Line Items] [Line Items] for Summary of Accounting Policies [Table] 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] Entity File Number Entity File Number Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Service Cost Defined Benefit Plan, Service Cost Decrease in Notes Payable Increase/(Decrease) in Notes Payable to Eversource Parent Proceeds from (Repayments of) Short-Term Debt Rate Reduction Bonds – Current Portion Rate Reduction Bonds - Current Portion Rate Reduction Bonds, Current Rate Reduction Bonds, Current Schedule of Contractual Maturities of Available-for-Sale Debt Securities Investments Classified by Contractual Maturity Date [Table Text Block] Offshore Wind Contingent Liability Offshore Wind Contingent Liability, Current Portion Offshore Wind Contingent Liability, Current Portion Corporate Debt Securities Corporate Bond Securities [Member] Sale of stock, issuance of common stock, maximum Sale of Stock, Issuance of Common Stock, Maximum Sale of Stock, Issuance of Common Stock, Maximum Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Issued as of (in shares) Common Stock, Shares, Issued Restricted Cash and Cash Equivalent Item [Line Items] Restricted Cash and Cash Equivalent Item [Line Items] Measure: Measure [Axis] Schedule of the Impact of Funding on the Balance Sheets and Income Statements Schedule of Variable Interest Entities [Table Text Block] Treasury stock, common (in shares) Treasury Stock, Common, Shares Schedule of Exposure to Guarantees and Indemnifications Schedule of Guarantor Obligations [Table Text Block] NSTAR Electric Series H Senior Notes NSTAR Electric Series H Senior Notes [Member] NSTAR Electric Series H Senior Notes Asset Retirement Obligations Asset Retirement Obligations, Noncurrent Wholesale Market Sales Revenues Wholesale Market Sales Revenue [Member] Wholesale Market Sales Revenue [Member] Total Retail Tariff Sales Revenues Total Retail Sales Revenue [Member] Total Retail Sales Revenue [Member] ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) Comprehensive Income (Loss) Note [Text Block] Operations, Excluding Storm Costs Operation Costs and Expenses, Excluding Storm Operation Costs and Expenses, Excluding Storm Yankee Gas, NSTAR Gas And EGMA Yankee Gas, NSTAR Gas And EGMA [Member] Yankee Gas, NSTAR Gas And EGMA Yankee Gas Series BB First Mortgage Bonds Yankee Gas Series BB First Mortgage Bonds [Member] Yankee Gas Series BB First Mortgage Bonds Equity Components [Axis] Equity Components [Axis] Product and Service [Domain] Product and Service [Domain] Related Party Related Party [Member] Class of Stock [Line Items] Class of Stock [Line Items] Regulatory Over Recoveries, Net Increase (Decrease) in Regulatory Assets and Liabilities Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] First Mortgage First Mortgage [Member] Entity Interactive Data Current Entity Interactive Data Current Net Income Attributable to Noncontrolling Interests Net Income Attributable to Noncontrolling Interests Net Income (Loss) Attributable to Noncontrolling Interest Loss on Offshore Wind Impairment of Ongoing Project Accumulated Deferred Income Taxes Deferred Income Tax Liabilities, Net Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] One to five years Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year One Through Five Capital Contributions from Eversource Parent Proceeds from Contributions from Parent Entity Smaller Reporting Company Entity Small Business Property, Plant and Equipment, Gross Public Utilities, Property, Plant and Equipment, Plant in Service Comprehensive Income Attributable to Common Shareholders Comprehensive Income (Loss), Net of Tax, Attributable to Parent Termination Date Trading Arrangement Termination Date Noncontrolling Interest [Table] Noncontrolling Interest [Table] Schedule of Supplemental Cash Flow [Line Items] Schedule of Supplemental Cash Flow [Line Items] [Line Items] for Schedule of Supplemental Cash Flow [Table] Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Settlements Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements SALE OF AQUARION WATER DISTRIBUTION BUSINESS Disposal Groups, Including Discontinued Operations, Disclosure [Text Block] Special Deposits Deposits Assets, Current Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] Changes in Funded Status of Pension, SERP and PBOP Benefit Plans Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] Other Current Liabilities Accrued Interest (included in Other Current Liabilities) Other Liabilities, Current Other Long-Term Assets Other Assets, Noncurrent Document Type Document Type 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] Securitized Stranded Costs Stranded Costs [Member] Fair Value as of Grant Date Award Grant Date Fair Value SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Significant Accounting Policies [Text Block] Site Contingency [Line Items] Site Contingency [Line Items] Proposed Cap Proposed Cap [Member] Proposed Cap Litigation settlement, amount Litigation Settlement, Amount Awarded from Other Party Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Money Market Funds Cash and Cash Equivalents [Member] Arrangement Duration Trading Arrangement Duration Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] 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 Issuance of Long-Term Debt Proceeds from Issuance of Long-Term Debt Local Phone Number Local Phone Number PBOP Other Postretirement Benefits Plan [Member] Consolidation Items [Axis] Consolidation Items [Axis] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Entity Registrant Name Entity Registrant Name Eversource Investment Service Company LLC Eversource Investment Service Company LLC [Member] Eversource Investment Service Company LLC Restrictions on Cash and Cash Equivalents [Table] Restrictions on Cash and Cash Equivalents [Table] Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Commitments and Contingencies (Note 9) Commitments and Contingencies Operating Revenues Total Operating Revenues Operating Revenues Revenues Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Executive Category: Executive Category [Axis] Uncollectible Costs Deferred Accounts Receivable, Allowance For Credit Loss, Deferred Expense (Reversal) Accounts Receivable, Allowance For Credit Loss, Deferred Expense (Reversal) Receivable Type [Axis] Receivable Type [Axis] 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. Counterparty Name [Axis] Counterparty Name [Axis] LIABILITIES AND CAPITALIZATION Liabilities and Equity [Abstract] 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 All Award Types Award Type [Domain] Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount FAIR VALUE OF FINANCIAL INSTRUMENTS Fair Value Disclosures [Text Block] Level 3 Fair Value, Inputs, Level 3 [Member] PEO Name PEO Name Debt assumed Disposal Group, Including Discontinued Operation, Consideration, Debt Assumed Disposal Group, Including Discontinued Operation, Consideration, Debt Assumed Connecticut, Massachusetts and New Hampshire Connecticut, Massachusetts and New Hampshire [Member] Connecticut, Massachusetts and New Hampshire [Member] Geographical [Axis] Geographical [Axis] Transmission - Electric Public Utilities, Property, Plant and Equipment, Transmission Qualified Cash Flow Hedging Instruments Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Other Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment Entity Tax Identification Number Entity Tax Identification Number Derivative Instruments and Hedging Activities Disclosures [Table] Derivative Instruments and Hedging Activities Disclosures [Table] Legal Entity [Axis] Legal Entity [Axis] Notes Payable Borrowings Outstanding as of Notes Payable Revolution Wind Tax Positions Revolution Wind Tax Positions [Member] Revolution Wind Tax Positions Cash, Cash Equivalents and Restricted Cash - Beginning of Period Cash, Cash Equivalents and Restricted Cash - End of Period Cash, Cash Equivalents and Restricted Cash as reported on the Statements of Cash Flows Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Issuance of Treasury Shares Stock Issued During Period, Value, Treasury Stock Reissued Equity method investment, liability obligations Equity Method Investment, Liability Obligations Equity Method Investment, Liability Obligations Schedule of Components of Other Income, Net Other Income, Net [Table Text Block] [Table Text Block] for Other Income, Net [Table] Accounts Payable Increase (Decrease) in Accounts Payable Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code 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 Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Non-NEOs Non-NEOs [Member] Approved cost recovery amount RAM proceeding Regulatory Asset, Approved Cost Recovery Amount RAM Proceeding Regulatory Asset, Approved Cost Recovery Amount RAM Proceeding 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] Financing Receivable, Allowance for Credit Loss [Roll Forward] Financing Receivable, Allowance for Credit Loss [Roll Forward] Debt Instrument [Axis] Debt Instrument [Axis] Yankee Gas Yankee Gas Services Company [Member] Ownership interest (percent) Equity Method Investment, Ownership Percentage ROE Type [Domain] ROE Type [Domain] ROE Type [Domain] Asset Retirement Obligations Asset Retirement Obligations [Member] Asset Retirement Obligations [Member] Disposal Group Name [Axis] Disposal Group Name [Axis] Schedule of Borrowings Outstanding Schedule of Debt [Table Text Block] Other Other [Member] Other [Member] Investment, Name [Domain] Investment, Name [Domain] Long-Term Debt, Type [Domain] Long-Term Debt, Type [Domain] Six to ten years Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 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] Basic Earnings Per Common Share (in dollars per share) Earnings Per Share, Basic Electric Transmission Electric Transmission Eversource Electric Transmission [Member] Eversource Electric Transmission [Member] Schedule of Regulatory Liabilities [Table] Regulated Operation, Regulatory Liability [Table] Total Current Assets Assets, Current Statistical Measurement [Axis] Statistical Measurement [Axis] Insider Trading Arrangements [Line Items] Sale of Aquarion Accounts Receivable, Allowance for Credit Loss, Sale Of Business Accounts Receivable, Allowance for Credit Loss, Sale Of Business Long-Term Debt Long-term debt Long-Term Debt, Excluding Current Maturities Award Type Award Type [Axis] Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Receivables, Net (net of allowance for uncollectible accounts) Accounts Receivable, after Allowance for Credit Loss, Current Retained Earnings Retained Earnings (Accumulated Deficit) 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. Product and Service [Axis] Product and Service [Axis] Noncontrolling Interest – Preferred Stock of Subsidiaries Preferred Stock Not Subject to Mandatory Redemption Noncontrolling interest attributed to preferred stock of subsidiaries Redeemable Noncontrolling Interest, Equity, Preferred, Carrying Amount Debt instrument, extension term Debt Instrument, Extension Term Debt Instrument, Extension Term Qualified Cash Flow Hedging Instruments Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax, Parent 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] Uncollectible Expense Operation Uncollectible Expenses Incurred Operation Uncollectible Expenses Incurred Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Pension and SERP Pension Plan [Member] Common Shares Common Stock Common Stock [Member] Fair Value Fair Value Debt Securities, Available-for-Sale Fair Value Measurement [Domain] Fair Value Measurement [Domain] Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Cover [Abstract] Cover [Abstract] Goodwill-related Goodwill Regulatory Asset [Member] Goodwill that originated from the merger that created NSTAR in 1999. Wholesale Transmission Revenues Wholesale Transmission Revenue [Member] Wholesale Transmission Revenue [Member] Weighted-average interest rate (in percent) Short-Term Debt, Weighted Average Interest Rate, at Point in Time Yankee Companies Yankee Companies [Member] Yankee Companies Dilutive Effect (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 AOCI Attributable to Parent [Roll Forward] AOCI Attributable to Parent [Abstract] Allowance for Uncollectible Accounts Receivable [Policy Text Block] Equity Awards Adjustments Equity Awards Adjustments [Member] Revolution Wind, LLC and TurbineCo, LLC Revolution Wind, LLC, and TurbineCo, LLC [Member] Revolution Wind, LLC, and TurbineCo, LLC Schedule of Marketable Securities Recorded at Fair Value on a Recurring Basis by Level Fair Value Hierarchy [Table Text Block] Fair Value Hierarchy [Table Text Block] Total Liabilities and Capitalization Liabilities and Equity Derivative Liabilities Derivative Liability, Noncurrent Regulatory Asset [Domain] Regulatory Asset [Domain] Employee Stock Option Share-Based Payment Arrangement, Option [Member] Rate Reduction Bonds Rate Reduction Bonds [Member] Rate Reduction Bonds [Member] Rate stabilization fund contribution Rate Stabilization Fund Contribution Rate Stabilization Fund Contribution Construction Work in Progress Public Utilities, Property, Plant and Equipment, Construction Work in Progress Segments [Axis] Segments [Axis] Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Asset Class [Axis] Asset Class [Axis] Retail (Non-Hardship), Wholesale, and Other Retail Non Hardship Wholesale and Other Receivables [Member] Retail Non Hardship Wholesale and Other Receivables [Member] Related Party [Domain] Related and Nonrelated Parties [Domain] Schedule of Allowance for Uncollectible Accounts Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Tabular List, Table Tabular List [Table Text Block] Capital Surplus, Paid In Additional Paid in Capital Other Income, Net Other Nonoperating Income (Expense) Residential Residential [Member] Residential [Member] Other Fixed Income Securities Other Debt Obligations [Member] Name Awards Close in Time to MNPI Disclosures, Individual Name 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] Deferred Debits and Other Assets: Assets, Noncurrent [Abstract] Corporate Shared Services General and Administrative Expense Amount of power to be purchased under capacity-related contract (in MW) Amount of Capacity Provided Under Capacity Contract Amount of Capacity Provided Under Capacity Contract The Connecticut Light and Power Company CL&P The Connecticut Light And Power Company [Member] Materials, Supplies, Natural Gas and REC Inventory Materials and Supplies Materials, Supplies and REC Inventory Inventory, Raw Materials and Supplies, Gross Regulatory liabilities Total Regulatory Liabilities Regulatory Liability Derivative Contract Derivative Asset [Member] Derivative Asset Adjustment to Compensation: Adjustment to Compensation [Axis] Equity in Earnings of Unconsolidated Affiliates Equity in Earnings (Loss) Of Unconsolidated Affiliate [Member] Equity in Earnings (Loss) And Impairment Of Unconsolidated Affiliate [Member] Public Service Company of New Hampshire PSNH Public Service Company Of New Hampshire (PSNH) [Member] Amounts Reclassified from AOCI Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Loss contingency, pending claims, number Loss Contingency, Pending Claims, Number Unrealized (losses) gains Marketable Security, Unrealized Gain (Loss) Pension, SERP and PBOP Non-Service   Income Components, Net of Deferred Portion Non-Service Cost Benefits [Member] Non-Service Cost Benefits [Member] Hardship Accounts Hardship Accounts [Member] Hardship Accounts [Member] Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Eversource TEI LLC Eversource TEI LLC [Member] Eversource TEI LLC Schedule of Common Shares Authorized and Issued Schedule of Stock by Class [Table Text Block] Credit Facility [Axis] Credit Facility [Axis] Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Discontinued Operations and Disposal Groups [Abstract] Name Measure Name Accounts Payable Accounts Payable, Current Pay vs Performance Disclosure [Line Items] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Other Other Noncash Income (Expense) Revolution Wind Revolution Wind [Member] Revolution Wind Debt Instrument [Line Items] Debt Instrument [Line Items] Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Capital Surplus, Paid In Additional Paid-in Capital [Member] Income Before Income Tax Expense Income (Loss) from Continuing Operations before Income Taxes, Domestic Entity Filer Category Entity Filer Category Final ROE Final ROE [Member] Final ROE Proceeds from sale of intangible assets Proceeds from Sale of Intangible Assets Guarantor Obligations, Nature [Domain] Guarantor Obligations, Nature [Domain] Percentage of base ROE of complaint period Percentage Of Base ROE Of Complaint Period Percentage Of Base ROE Of Complaint Period Alternative Revenue Programs Revenue Not from Contract with Customer 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. Name Trading Arrangement, Individual Name Schedule of Components of Regulatory Assets Schedule of Regulatory Assets [Table Text Block] Cash and Cash Equivalents Cash and cash equivalent Cash and Cash Equivalents as reported on the Balance Sheets Cash and Cash Equivalent Interest component of regulatory liability Interest Component Of Regulatory Liability Interest Component Of Regulatory Liability Company Selected Measure Amount Company Selected Measure Amount Depreciation and Amortization Depreciation, Depletion and Amortization Investments, Debt and Equity Securities [Abstract] Investments, Debt and Equity Securities [Abstract] Entity Address, Address Line Two Entity Address, Address Line Two Schedule of Stock by Class [Table] Stock, Class of Stock [Table] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Accounts and Financing Receivables [Table] Net Income Net Income Net Income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Current Assets: Assets, Current [Abstract] Proposed ROE Proposed ROE [Member] Proposed ROE Non-PEO NEO Non-PEO NEO [Member] Senior Notes Senior Notes [Member] Entity Address, Address Line One Entity Address, Address Line One Previous Order ROE Previous Order ROE [Member] Previous Order ROE Income Tax Expense Income Tax (Expense)/Benefit Income Tax Expense (Benefit) Approved cost recovery amount for securitization Regulatory Assets, Approved Cost Recovery Amount For Securitization Regulatory Assets, Approved Cost Recovery Amount For Securitization Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Noncash Item [Abstract] Award Timing Method Award Timing Method [Text Block] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Net (Decrease)/Increase in Cash and Restricted Cash Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Natural Gas Distribution Natural Gas Distribution Natural Gas Distribution [Member] VIE Variable Interest Entity, Primary Beneficiary [Member] Actuarial Loss/(Gain) Defined Benefit Plan, Amortization of Gain (Loss) Net Income Net Income Net Income (Loss) Attributable to Parent Long-Term Debt, Type [Axis] Long-Term Debt, Type [Axis] Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Eversource Parent Series AA Senior Notes Eversource Parent Series AA Senior Notes [Member] Eversource Parent Series AA Senior Notes Goodwill Disposal Group, Including Discontinued Operation, Goodwill Balance Sheet Location [Axis] Location, Statement of Financial Position, Balance [Axis] Statement [Table] Statement [Table] Environmental Remediation Site [Domain] Environmental Remediation Site [Domain] 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] Restatement Determination Date: Restatement Determination Date [Axis] Regulatory Liabilities Less:  Current Portion Regulatory Liability, Current Schedule of Changes in Accumulated Other Comprehensive Income/(Loss) by Component, Net of Tax Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Interest Income Investment Income, Interest Power purchase agreement Derivative, Contract Term Public Utility, Property, Plant and Equipment [Line Items] Public Utility, Property, Plant and Equipment [Line Items] Total Deferred Credits and Other Liabilities Liabilities, Other than Long-Term Debt, Noncurrent Other Regulatory Liabilities Other Regulatory Liabilities [Member] Represents various remaining other regulatory liabilities. Derivative Instruments and Hedging Activities Disclosures [Line Items] Derivative Instruments and Hedging Activities Disclosures [Line Items] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Current Derivative Assets Derivative Asset, Subject to Master Netting Arrangement, before Offset Condensed Income Statements, Captions [Line Items] Condensed Income Statements, Captions [Line Items] Condensed Balance Sheet Statements, Captions [Line Items] Condensed Balance Sheet Statements, Captions [Line Items] Schedule of Derivative Assets and Derivative Liabilities Measured at Fair Value Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Document And Entity [Line Items] Document And Entity [Line Items] Schedule of Supplemental Cash Flow [Table] Schedule of Supplemental Cash Flow [Table] Schedule of Supplemental Cash Flow [Table] Accrued Taxes Accrued Income Taxes Cost of Removal Expenditures Regulatory Assets, Removal Costs (Income) Regulatory Assets, Removal Costs (Income) Damages sought Loss Contingency, Damages Sought, Value Number of regulated utilities Number Of Regulated Utilities Number Of Regulated Utilities Recoveries Collected Accounts Receivable, Allowance for Credit Loss, Recovery Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative Instruments and Hedging Activities Disclosure [Abstract]