3.3.1.900 html 1050 567 1 false 188 0 false 7 false false R1.htm 100000 - Document - DOCUMENT AND ENTITY INFORMATION Sheet http://www.eversource.com/role/DOCUMENTANDENTITYINFORMATION DOCUMENT AND ENTITY INFORMATION Cover 1 false false R2.htm 100010 - Statement - CONSOLIDATED BALANCE SHEETS Sheet http://www.eversource.com/role/StatementCONSOLIDATEDBALANCESHEETS CONSOLIDATED BALANCE SHEETS Statements 2 false false R3.htm 100020 - Statement - CONSOLIDATED STATEMENTS OF INCOME Sheet http://www.eversource.com/role/StatementCONSOLIDATEDSTATEMENTSOFINCOME CONSOLIDATED STATEMENTS OF INCOME Statements 3 false false R4.htm 100025 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME Sheet http://www.eversource.com/role/StatementCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOME CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME Statements 4 false false R5.htm 100050 - Statement - CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS EQUITY Sheet http://www.eversource.com/role/StatementCONSOLIDATEDSTATEMENTSOFCOMMONSHAREHOLDERSEQUITY CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS EQUITY Statements 5 false false R6.htm 100055 - Statement - CONSOLIDATED STATEMENT OF CASH FLOWS Sheet http://www.eversource.com/role/StatementCONSOLIDATEDSTATEMENTOFCASHFLOWS CONSOLIDATED STATEMENT OF CASH FLOWS Statements 6 false false R7.htm 100060 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Sheet http://www.eversource.com/role/DisclosureSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIES SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Notes 7 false false R8.htm 100075 - Disclosure - REGULATORY ACCOUNTING Sheet http://www.eversource.com/role/DisclosureREGULATORYACCOUNTING REGULATORY ACCOUNTING Notes 8 false false R9.htm 100080 - Disclosure - PROPERTY, PLANT AND ACCUMULATED DEPRECIATION Sheet http://www.eversource.com/role/DisclosurePROPERTYPLANTANDACCUMULATEDDEPRECIATION PROPERTY, PLANT AND ACCUMULATED DEPRECIATION Notes 9 false false R10.htm 100090 - Disclosure - DERIVATIVE INSTRUMENTS Sheet http://www.eversource.com/role/DisclosureDERIVATIVEINSTRUMENTS DERIVATIVE INSTRUMENTS Notes 10 false false R11.htm 100100 - Disclosure - MARKETABLE SECURITIES Sheet http://www.eversource.com/role/DisclosureMARKETABLESECURITIES MARKETABLE SECURITIES Notes 11 false false R12.htm 100105 - Disclosure - ASSET RETIREMENT OBLIGATIONS Sheet http://www.eversource.com/role/ASSETRETIREMENTOBLIGATIONS ASSET RETIREMENT OBLIGATIONS Notes 12 false false R13.htm 100141 - Disclosure - SHORT TERM DEBT Sheet http://www.eversource.com/role/SHORTTERMDEBT SHORT TERM DEBT Notes 13 false false R14.htm 100144 - Disclosure - LONG-TERM DEBT Sheet http://www.eversource.com/role/LONGTERMDEBT LONG-TERM DEBT Notes 14 false false R15.htm 100150 - Disclosure - PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSIONS Sheet http://www.eversource.com/role/DisclosurePENSIONBENEFITSANDPOSTRETIREMENTBENEFITSOTHERTHANPENSIONS PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSIONS Notes 15 false false R16.htm 100151 - Disclosure - DEFINED CONTRIBUTION PLANS Sheet http://www.eversource.com/role/DEFINEDCONTRIBUTIONPLANS DEFINED CONTRIBUTION PLANS Notes 16 false false R17.htm 100153 - Disclosure - SHARE-BASED PAYMENTS Sheet http://www.eversource.com/role/DisclosureSHAREBASEDPAYMENTS SHARE-BASED PAYMENTS Notes 17 false false R18.htm 100155 - Disclosure - OTHER RETIREMENT BENEFITS Sheet http://www.eversource.com/role/OTHERRETIREMENTBENEFITS OTHER RETIREMENT BENEFITS Notes 18 false false R19.htm 100160 - Disclosure - INCOME TAXES Sheet http://www.eversource.com/role/DisclosureINCOMETAXES INCOME TAXES Notes 19 false false R20.htm 100170 - Disclosure - COMMITMENTS AND CONTINGENCIES Sheet http://www.eversource.com/role/DisclosureCOMMITMENTSANDCONTINGENCIES COMMITMENTS AND CONTINGENCIES Notes 20 false false R21.htm 100180 - Disclosure - LEASES Sheet http://www.eversource.com/role/LEASES LEASES Notes 21 false false R22.htm 100190 - Disclosure - FAIR VALUE OF FINANCIAL INSTRUMENTS Sheet http://www.eversource.com/role/DisclosureFAIRVALUEOFFINANCIALINSTRUMENTS FAIR VALUE OF FINANCIAL INSTRUMENTS Notes 22 false false R23.htm 100210 - Disclosure - ACCUMULATED OTHER COMPREHENSIVE INCOME Sheet http://www.eversource.com/role/ACCUMULATEDOTHERCOMPREHENSIVEINCOME ACCUMULATED OTHER COMPREHENSIVE INCOME Notes 23 false false R24.htm 100229 - Disclosure - DIVIDEND RESTRICTIONS Sheet http://www.eversource.com/role/DIVIDENDRESTRICTIONS DIVIDEND RESTRICTIONS Notes 24 false false R25.htm 100230 - Disclosure - COMMON SHARES Sheet http://www.eversource.com/role/COMMONSHARES COMMON SHARES Notes 25 false false R26.htm 100233 - Disclosure - PREFFERED STOCK NOT SUBJECT TO MANDATORY REDEMPTION Sheet http://www.eversource.com/role/DisclosurePREFFEREDSTOCKNOTSUBJECTTOMANDATORYREDEMPTION PREFFERED STOCK NOT SUBJECT TO MANDATORY REDEMPTION Notes 26 false false R27.htm 100240 - Disclosure - COMMON SHARESHOLDERS' EQUITY AND NONCONTROLLING INTERESTS (NU) Sheet http://www.eversource.com/role/DisclosureCOMMONSHARESHOLDERSEQUITYANDNONCONTROLLINGINTERESTSNU COMMON SHARESHOLDERS' EQUITY AND NONCONTROLLING INTERESTS (NU) Notes 27 false false R28.htm 100250 - Disclosure - EARNINGS PER SHARE Sheet http://www.eversource.com/role/DisclosureEARNINGSPERSHARE EARNINGS PER SHARE Notes 28 false false R29.htm 100260 - Disclosure - SEGMENT INFORMATION Sheet http://www.eversource.com/role/DisclosureSEGMENTINFORMATION SEGMENT INFORMATION Notes 29 false false R30.htm 100266 - Disclosure - GOODWILL Sheet http://www.eversource.com/role/GOODWILL GOODWILL Notes 30 false false R31.htm 100270 - Disclosure - VARIABLE INTEREST ENTITIES Sheet http://www.eversource.com/role/DisclosureVARIABLEINTERESTENTITIES VARIABLE INTEREST ENTITIES Notes 31 false false R32.htm 100281 - Disclosure - QUARTERLY FINANCIAL DATA (Unaudited) Sheet http://www.eversource.com/role/QUARTERLYFINANCIALDATAUnaudited QUARTERLY FINANCIAL DATA (Unaudited) Notes 32 false false R33.htm 200000 - Disclosure - SIGNIFCANT ACCOUNTING POLICIES (Policies) Sheet http://www.eversource.com/role/DisclosureSIGNIFCANTACCOUNTINGPOLICIESPolicies SIGNIFCANT ACCOUNTING POLICIES (Policies) Policies 33 false false R34.htm 300002 - Disclosure - Provision for Uncollectible Accounts (Tables) Sheet http://www.eversource.com/role/ProvisionForUncollectibleAccountsTables Provision for Uncollectible Accounts (Tables) Tables 34 false false R35.htm 300003 - Disclosure - Fuel Materials and Supplies and Allowance Inventory (Tables) Sheet http://www.eversource.com/role/FuelMaterialsAndSuppliesAndAllowanceInventoryTables Fuel Materials and Supplies and Allowance Inventory (Tables) Tables 35 false false R36.htm 300004 - Disclosure - Equity Method Investments (Tables) Sheet http://www.eversource.com/role/EquityMethodInvestmentsTables Equity Method Investments (Tables) Tables 36 false false R37.htm 300006 - Disclosure - Operating Expenses (Tables) Sheet http://www.eversource.com/role/OperatingExpensesTables Operating Expenses (Tables) Tables 37 false false R38.htm 300010 - Disclosure - Allowance for Funds Used During Construction (Tables) Sheet http://www.eversource.com/role/DisclosureAllowanceForFundsUsedDuringConstructionTables Allowance for Funds Used During Construction (Tables) Tables 38 false false R39.htm 300030 - Disclosure - Other Taxes (Tables) Sheet http://www.eversource.com/role/DisclosureOtherTaxesTables Other Taxes (Tables) Tables 39 false false R40.htm 300040 - Disclosure - Supplemental Cash Flow Information (Tables) Sheet http://www.eversource.com/role/DisclosureSupplementalCashFlowInformationTables Supplemental Cash Flow Information (Tables) Tables 40 false false R41.htm 300070 - Disclosure - REGULATORY ACCOUNTING (Tables) Sheet http://www.eversource.com/role/DisclosureREGULATORYACCOUNTINGTables REGULATORY ACCOUNTING (Tables) Tables http://www.eversource.com/role/DisclosureREGULATORYACCOUNTING 41 false false R42.htm 300080 - Disclosure - PROPERTY, PLANT AND ACCUMULATED DEPRECIATION (Tables) Sheet http://www.eversource.com/role/DisclosurePROPERTYPLANTANDACCUMULATEDDEPRECIATIONTables PROPERTY, PLANT AND ACCUMULATED DEPRECIATION (Tables) Tables http://www.eversource.com/role/DisclosurePROPERTYPLANTANDACCUMULATEDDEPRECIATION 42 false false R43.htm 300090 - Disclosure - DERIVATIVE INSTRUMENTS (Tables) Sheet http://www.eversource.com/role/DisclosureDERIVATIVEINSTRUMENTSTables DERIVATIVE INSTRUMENTS (Tables) Tables http://www.eversource.com/role/DisclosureDERIVATIVEINSTRUMENTS 43 false false R44.htm 300100 - Disclosure - MARKETABLE SECURITIES (Tables) Sheet http://www.eversource.com/role/DisclosureMARKETABLESECURITIESTables MARKETABLE SECURITIES (Tables) Tables http://www.eversource.com/role/DisclosureMARKETABLESECURITIES 44 false false R45.htm 300110 - Disclosure - ASSET RETIREMENT OBLIGATIONS (TABLE) Sheet http://www.eversource.com/role/ASSETRETIREMENTOBLIGATIONSTABLE ASSET RETIREMENT OBLIGATIONS (TABLE) Uncategorized 45 false false R46.htm 300140 - Disclosure - LONG-TERM DEBT (TABLES) Sheet http://www.eversource.com/role/DisclosureLONGTERMDEBTTABLES LONG-TERM DEBT (TABLES) Uncategorized 46 false false R47.htm 300150 - Disclosure - Pension Benefits and Postretirement Benefits Other Than Pensions (Tables) Sheet http://www.eversource.com/role/PensionBenefitsAndPostretirementBenefitsOtherThanPensionsTables Pension Benefits and Postretirement Benefits Other Than Pensions (Tables) Uncategorized 47 false false R48.htm 300152 - Disclosure - DEFINED CONTRIBUTION PLANS (TABLES) Sheet http://www.eversource.com/role/DEFINEDCONTRIBUTIONPLANSTABLES DEFINED CONTRIBUTION PLANS (TABLES) Uncategorized 48 false false R49.htm 300154 - Disclosure - Share-Based Payments (Tables) Sheet http://www.eversource.com/role/ShareBasedPaymentsTables Share-Based Payments (Tables) Uncategorized 49 false false R50.htm 300156 - Disclosure - Other Retirement Benefits (Tables) Sheet http://www.eversource.com/role/OtherRetirementBenefitsTables Other Retirement Benefits (Tables) Uncategorized 50 false false R51.htm 300158 - Disclosure - INCOME TAXES (Tables) Sheet http://www.eversource.com/role/DisclosureINCOMETAXESTables INCOME TAXES (Tables) Uncategorized 51 false false R52.htm 300160 - Disclosure - Environmental Matters (Tables) Sheet http://www.eversource.com/role/EnvironmentalMattersTables Environmental Matters (Tables) Uncategorized 52 false false R53.htm 300165 - Disclosure - Long-Term Contractual Arrangements (Tables) Sheet http://www.eversource.com/role/LongTermContractualArrangementsTables Long-Term Contractual Arrangements (Tables) Uncategorized 53 false false R54.htm 300170 - Disclosure - Guarantees and Indemnifications (Tables) Sheet http://www.eversource.com/role/DisclosureGuaranteesAndIndemnificationsTables Guarantees and Indemnifications (Tables) Uncategorized 54 false false R55.htm 300180 - Disclosure - LEASES (Tables) Sheet http://www.eversource.com/role/LEASESTables LEASES (Tables) Uncategorized 55 false false R56.htm 300190 - Disclosure - FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables) Sheet http://www.eversource.com/role/DisclosureFAIRVALUEOFFINANCIALINSTRUMENTSTables FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables) Uncategorized 56 false false R57.htm 300210 - Disclosure - ACCUMULATED OTHER COMPREHENSIVE INCOME (Tables) Sheet http://www.eversource.com/role/DisclosureACCUMULATEDOTHERCOMPREHENSIVEINCOMETables ACCUMULATED OTHER COMPREHENSIVE INCOME (Tables) Uncategorized 57 false false R58.htm 300230 - Disclosure - COMMON SHARES (Tables) Sheet http://www.eversource.com/role/DisclosureCOMMONSHARESTables COMMON SHARES (Tables) Uncategorized 58 false false R59.htm 300235 - Disclosure - PREFFERED STOCK (TABLES) Sheet http://www.eversource.com/role/PREFFEREDSTOCKTABLES PREFFERED STOCK (TABLES) Uncategorized 59 false false R60.htm 300240 - Disclosure - COMMON SHARESHOLDERS' EQUITY AND NONCONTROLLING INTERESTS (NU) (Tables) Sheet http://www.eversource.com/role/DisclosureCOMMONSHARESHOLDERSEQUITYANDNONCONTROLLINGINTERESTSNUTables COMMON SHARESHOLDERS' EQUITY AND NONCONTROLLING INTERESTS (NU) (Tables) Uncategorized 60 false false R61.htm 300250 - Disclosure - EARNINGS PER SHARE (Tables) Sheet http://www.eversource.com/role/DisclosureEARNINGSPERSHARETables EARNINGS PER SHARE (Tables) Uncategorized 61 false false R62.htm 300260 - Disclosure - SEGMENT INFORMATION (Tables) Sheet http://www.eversource.com/role/DisclosureSEGMENTINFORMATIONTables SEGMENT INFORMATION (Tables) Uncategorized 62 false false R63.htm 300263 - Disclosure - GOODWILL (Tables) Sheet http://www.eversource.com/role/DisclosureGOODWILLTables GOODWILL (Tables) Uncategorized 63 false false R64.htm 300290 - Disclosure - QUARTERLY FINANCIAL DATA (Unaudited) (Tables) Sheet http://www.eversource.com/role/QUARTERLYFINANCIALDATAUnauditedTables QUARTERLY FINANCIAL DATA (Unaudited) (Tables) Uncategorized 64 false false R65.htm 400002 - Disclosure - ACCOUNTING STANDARDS (Details) Sheet http://www.eversource.com/role/DisclosureACCOUNTINGSTANDARDSDetails ACCOUNTING STANDARDS (Details) Uncategorized 65 false false R66.htm 400020 - Disclosure - Provision for Uncollectible Accounts (Details) Sheet http://www.eversource.com/role/DisclosureProvisionForUncollectibleAccountsDetails Provision for Uncollectible Accounts (Details) Uncategorized 66 false false R67.htm 400025 - Disclosure - Fuel, Materials and Supplies and Allowance Inventory (Details) Sheet http://www.eversource.com/role/DisclosureFuelMaterialsAndSuppliesAndAllowanceInventoryDetails Fuel, Materials and Supplies and Allowance Inventory (Details) Uncategorized 67 false false R68.htm 400030 - Disclosure - Deposits (Details) Sheet http://www.eversource.com/role/DepositsDetails Deposits (Details) Uncategorized 68 false false R69.htm 400031 - Disclosure - Equity Method Investments (Details) Sheet http://www.eversource.com/role/DisclosureEquityMethodInvestmentsDetails Equity Method Investments (Details) Uncategorized 69 false false R70.htm 400045 - Disclosure - Operating Expenses (Details) Sheet http://www.eversource.com/role/OperatingExpensesDetails Operating Expenses (Details) Uncategorized 70 false false R71.htm 400050 - Disclosure - Allowance for Funds Used During Construction (Details) Sheet http://www.eversource.com/role/DisclosureAllowanceForFundsUsedDuringConstructionDetails Allowance for Funds Used During Construction (Details) Uncategorized 71 false false R72.htm 400050 - Disclosure - Other Income, Net (Details) Sheet http://www.eversource.com/role/DisclosureOtherIncomeNetDetails Other Income, Net (Details) Uncategorized 72 false false R73.htm 400060 - Disclosure - Other Taxes (Details) Sheet http://www.eversource.com/role/DisclosureOtherTaxesDetails Other Taxes (Details) Uncategorized 73 false false R74.htm 400070 - Disclosure - Supplemental Cash Flow Information (Details) Sheet http://www.eversource.com/role/DisclosureSupplementalCashFlowInformationDetails Supplemental Cash Flow Information (Details) Uncategorized 74 false false R75.htm 400072 - Disclosure - Severance Benefits (Details) Sheet http://www.eversource.com/role/SeveranceBenefitsDetails Severance Benefits (Details) Uncategorized 75 false false R76.htm 400075 - Disclosure - Related Parties (Details) Sheet http://www.eversource.com/role/RelatedPartiesDetails Related Parties (Details) Uncategorized 76 false false R77.htm 400080 - Disclosure - REGULATORY ACCOUNTING (Details) Sheet http://www.eversource.com/role/DisclosureREGULATORYACCOUNTINGDetails REGULATORY ACCOUNTING (Details) Uncategorized 77 false false R78.htm 400090 - Disclosure - PROPERTY, PLANT AND ACCUMULATED DEPRECIATION (Details) Sheet http://www.eversource.com/role/DisclosurePROPERTYPLANTANDACCUMULATEDDEPRECIATIONDetails PROPERTY, PLANT AND ACCUMULATED DEPRECIATION (Details) Uncategorized 78 false false R79.htm 400095 - Disclosure - DERIVATIVE INSTURMENTS (Details) Sheet http://www.eversource.com/role/DisclosureDERIVATIVEINSTURMENTSDetails DERIVATIVE INSTURMENTS (Details) Uncategorized 79 false false R80.htm 400096 - Disclosure - Fair Value Measurements (Details) Sheet http://www.eversource.com/role/DisclosureFairValueMeasurementsDetails Fair Value Measurements (Details) Uncategorized 80 false false R81.htm 400110 - Disclosure - MARKETABLE SECURITIES (Details) Sheet http://www.eversource.com/role/DisclosureMARKETABLESECURITIESDetails MARKETABLE SECURITIES (Details) Uncategorized 81 false false R82.htm 400115 - Disclosure - ASSET RETIREMENT OBLIGATIONS (Details) Sheet http://www.eversource.com/role/DisclosureASSETRETIREMENTOBLIGATIONSDetails ASSET RETIREMENT OBLIGATIONS (Details) Uncategorized 82 false false R83.htm 400118 - Disclosure - SHORT-TERM DEBT (Details) Sheet http://www.eversource.com/role/DisclosureSHORTTERMDEBTDetails SHORT-TERM DEBT (Details) Uncategorized 83 false false R84.htm 400119 - Disclosure - LONG-TERM DEBT (Details) Sheet http://www.eversource.com/role/DisclosureLONGTERMDEBTDetails LONG-TERM DEBT (Details) Uncategorized 84 false false R85.htm 400120 - Disclosure - PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSIONS (Details) Sheet http://www.eversource.com/role/DisclosurePENSIONBENEFITSANDPOSTRETIREMENTBENEFITSOTHERTHANPENSIONSDetails PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSIONS (Details) Uncategorized 85 false false R86.htm 400121 - Disclosure - Defined Contribution Plans (Details) Sheet http://www.eversource.com/role/DisclosureDefinedContributionPlansDetails Defined Contribution Plans (Details) Uncategorized 86 false false R87.htm 400122 - Disclosure - Employee Stock Ownership Plan (Details) Sheet http://www.eversource.com/role/DisclosureEmployeeStockOwnershipPlanDetails Employee Stock Ownership Plan (Details) Uncategorized 87 false false R88.htm 400123 - Disclosure - Share-Based Payments (Details) Sheet http://www.eversource.com/role/DisclosureShareBasedPaymentsDetails Share-Based Payments (Details) Uncategorized 88 false false R89.htm 400128 - Disclosure - INCOME TAXES (Details) Sheet http://www.eversource.com/role/DisclosureINCOMETAXESDetails INCOME TAXES (Details) Uncategorized 89 false false R90.htm 400130 - Disclosure - Environmental Matters (Details) Sheet http://www.eversource.com/role/DisclosureEnvironmentalMattersDetails Environmental Matters (Details) Uncategorized 90 false false R91.htm 400131 - Disclosure - Long-Term Contractual Arrangements (Details) Sheet http://www.eversource.com/role/DisclosureLongTermContractualArrangementsDetails Long-Term Contractual Arrangements (Details) Uncategorized 91 false false R92.htm 400136 - Disclosure - Contractual Obligations with Yankee Companies (Details) Sheet http://www.eversource.com/role/DisclosureContractualObligationsWithYankeeCompaniesDetails Contractual Obligations with Yankee Companies (Details) Uncategorized 92 false false R93.htm 400140 - Disclosure - Guarantees and Indemnifications (Details) Sheet http://www.eversource.com/role/DisclosureGuaranteesAndIndemnificationsDetails Guarantees and Indemnifications (Details) Uncategorized 93 false false R94.htm 400147 - Disclosure - Other Contingencies (Details) Sheet http://www.eversource.com/role/DisclosureOtherContingenciesDetails Other Contingencies (Details) Uncategorized 94 false false R95.htm 400154 - Disclosure - LEASES (Details) Sheet http://www.eversource.com/role/LEASESDetails LEASES (Details) Uncategorized 95 false false R96.htm 400155 - Disclosure - FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) Sheet http://www.eversource.com/role/FAIRVALUEOFFINANCIALINSTRUMENTSDetails FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) Uncategorized 96 false false R97.htm 400160 - Disclosure - ACCUMULATED OTHER COMPREHENSIVE INCOME (Details) Sheet http://www.eversource.com/role/DisclosureACCUMULATEDOTHERCOMPREHENSIVEINCOMEDetails ACCUMULATED OTHER COMPREHENSIVE INCOME (Details) Uncategorized 97 false false R98.htm 400169 - Disclosure - DIVIDEND RESTRICTIONS (Details) Sheet http://www.eversource.com/role/DisclosureDIVIDENDRESTRICTIONSDetails DIVIDEND RESTRICTIONS (Details) Uncategorized 98 false false R99.htm 400170 - Disclosure - COMMON SHARES (Details) Sheet http://www.eversource.com/role/DisclosureCOMMONSHARESDetails COMMON SHARES (Details) Uncategorized 99 false false R100.htm 400175 - Disclosure - PREFFERED STOCK NOT SUBJECT TO MANDATORY REDEMPTION (DETAILS) Sheet http://www.eversource.com/role/DisclosurePREFFEREDSTOCKNOTSUBJECTTOMANDATORYREDEMPTIONDETAILS PREFFERED STOCK NOT SUBJECT TO MANDATORY REDEMPTION (DETAILS) Uncategorized 100 false false R101.htm 400181 - Disclosure - COMMON SHAREHOLDER EQUIT AND NCI (Details) Sheet http://www.eversource.com/role/DisclosureCOMMONSHAREHOLDEREQUITANDNCIDetails COMMON SHAREHOLDER EQUIT AND NCI (Details) Uncategorized 101 false false R102.htm 400190 - Disclosure - EARNINGS PER SHARE (Details) Sheet http://www.eversource.com/role/EARNINGSPERSHAREDetails EARNINGS PER SHARE (Details) Uncategorized 102 false false R103.htm 400200 - Disclosure - SEGMENT INFORMATION (Details) Sheet http://www.eversource.com/role/DisclosureSEGMENTINFORMATIONDetails SEGMENT INFORMATION (Details) Uncategorized 103 false false R104.htm 400202 - Disclosure - GOODWILL (Details) Sheet http://www.eversource.com/role/DisclosureGOODWILLDetails GOODWILL (Details) Uncategorized 104 false false R105.htm 400204 - Disclosure - QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) Sheet http://www.eversource.com/role/DisclosureQUARTERLYFINANCIALDATAUNAUDITEDDetails QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) Uncategorized 105 false false R106.htm 400210 - Disclosure - SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES (Details) Sheet http://www.eversource.com/role/DisclosureSCHEDULEIIVALUATIONANDQUALIFYINGACCOUNTSANDRESERVESDetails SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES (Details) Uncategorized 106 false false All Reports Book All Reports es-20151231.xml es-20151231.xsd es-20151231_cal.xml es-20151231_def.xml es-20151231_lab.xml es-20151231_pre.xml true true