<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.22.0.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>1534</ContextCount>
  <ElementCount>826</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>291</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>17</UnitCount>
  <MyReports>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>000010001 - Document - COVER PAGE</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COVERPAGE</Role>
      <ShortName>COVER PAGE</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>000020002 - Document - Audit Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/AuditInformation</Role>
      <ShortName>Audit Information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>100010003 - Statement - CONSOLIDATED BALANCE SHEETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/CONSOLIDATEDBALANCESHEETS</Role>
      <ShortName>CONSOLIDATED BALANCE SHEETS</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>100020004 - Statement - CONSOLIDATED BALANCE SHEETS (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/CONSOLIDATEDBALANCESHEETSParenthetical</Role>
      <ShortName>CONSOLIDATED BALANCE SHEETS (Parenthetical)</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>100030005 - Statement - CONSOLIDATED STATEMENTS OF INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/CONSOLIDATEDSTATEMENTSOFINCOME</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>100040006 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/CONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOME</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>100050007 - Statement - CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS' EQUITY</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/CONSOLIDATEDSTATEMENTSOFCOMMONSHAREHOLDERSEQUITY</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS' EQUITY</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>100060008 - Statement - CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS' EQUITY (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/CONSOLIDATEDSTATEMENTSOFCOMMONSHAREHOLDERSEQUITYParenthetical</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS' EQUITY (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>100070009 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/CONSOLIDATEDSTATEMENTSOFCASHFLOWS</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF CASH FLOWS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>100080010 - Statement - THE CONNECTICUT LIGHT AND POWER COMPANY BALANCE SHEETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/THECONNECTICUTLIGHTANDPOWERCOMPANYBALANCESHEETS</Role>
      <ShortName>THE CONNECTICUT LIGHT AND POWER COMPANY BALANCE SHEETS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>100090011 - Statement - CONSOLIDATED BALANCE SHEETS (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/CONSOLIDATEDBALANCESHEETSParenthetical_1</Role>
      <ShortName>CONSOLIDATED BALANCE SHEETS (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>100100012 - Statement - THE CONNECTICUT LIGHT AND POWER COMPANY STATEMENTS OF INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/THECONNECTICUTLIGHTANDPOWERCOMPANYSTATEMENTSOFINCOME</Role>
      <ShortName>THE CONNECTICUT LIGHT AND POWER COMPANY STATEMENTS OF INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>100110013 - Statement - THE CONNECTICUT LIGHT AND POWER COMPANY STATEMENTS OF COMPREHENSIVE INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/THECONNECTICUTLIGHTANDPOWERCOMPANYSTATEMENTSOFCOMPREHENSIVEINCOME</Role>
      <ShortName>THE CONNECTICUT LIGHT AND POWER COMPANY STATEMENTS OF COMPREHENSIVE INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>100120014 - Statement - THE CONNECTICUT LIGHT AND POWER COMPANY STATEMENTS OF COMMON STOCKHOLDER'S EQUITY</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/THECONNECTICUTLIGHTANDPOWERCOMPANYSTATEMENTSOFCOMMONSTOCKHOLDERSEQUITY</Role>
      <ShortName>THE CONNECTICUT LIGHT AND POWER COMPANY STATEMENTS OF COMMON STOCKHOLDER'S EQUITY</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>100130015 - Statement - THE CONNECTICUT LIGHT AND POWER COMPANY STATEMENTS OF CASH FLOWS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/THECONNECTICUTLIGHTANDPOWERCOMPANYSTATEMENTSOFCASHFLOWS</Role>
      <ShortName>THE CONNECTICUT LIGHT AND POWER COMPANY STATEMENTS OF CASH FLOWS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>100140016 - Statement - NSTAR ELECTRIC COMPANY AND SUBSIDIARY CONSOLIDATED BALANCE SHEETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/NSTARELECTRICCOMPANYANDSUBSIDIARYCONSOLIDATEDBALANCESHEETS</Role>
      <ShortName>NSTAR ELECTRIC COMPANY AND SUBSIDIARY CONSOLIDATED BALANCE SHEETS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>100150017 - Statement - NSTAR ELECTRIC COMPANY AND SUBSIDIARY CONSOLIDATED BALANCE SHEETS (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/NSTARELECTRICCOMPANYANDSUBSIDIARYCONSOLIDATEDBALANCESHEETSParenthetical</Role>
      <ShortName>NSTAR ELECTRIC COMPANY AND SUBSIDIARY CONSOLIDATED BALANCE SHEETS (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>100160018 - Statement - NSTAR ELECTRIC COMPANY AND SUBSIDIARY CONSOLIDATED STATEMENTS OF INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/NSTARELECTRICCOMPANYANDSUBSIDIARYCONSOLIDATEDSTATEMENTSOFINCOME</Role>
      <ShortName>NSTAR ELECTRIC COMPANY AND SUBSIDIARY CONSOLIDATED STATEMENTS OF INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>100170019 - Statement - NSTAR ELECTRIC COMPANY AND SUBSIDIARY CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/NSTARELECTRICCOMPANYANDSUBSIDIARYCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOME</Role>
      <ShortName>NSTAR ELECTRIC COMPANY AND SUBSIDIARY CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>100180020 - Statement - NSTAR ELECTRIC COMPANY AND SUBSIDIARY CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDER'S EQUITY</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/NSTARELECTRICCOMPANYANDSUBSIDIARYCONSOLIDATEDSTATEMENTSOFCOMMONSTOCKHOLDERSEQUITY</Role>
      <ShortName>NSTAR ELECTRIC COMPANY AND SUBSIDIARY CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDER'S EQUITY</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>100190021 - Statement - NSTAR ELECTRIC COMPANY AND SUBSIDIARY CONSOLIDATED STATEMENTS OF CASH FLOWS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/NSTARELECTRICCOMPANYANDSUBSIDIARYCONSOLIDATEDSTATEMENTSOFCASHFLOWS</Role>
      <ShortName>NSTAR ELECTRIC COMPANY AND SUBSIDIARY CONSOLIDATED STATEMENTS OF CASH FLOWS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>100200022 - Statement - PUBLIC SERVICE COMPANY OF NEW HAMPSHIRE AND SUBSIDIARIES CONSOLIDATED BALANCE SHEETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/PUBLICSERVICECOMPANYOFNEWHAMPSHIREANDSUBSIDIARIESCONSOLIDATEDBALANCESHEETS</Role>
      <ShortName>PUBLIC SERVICE COMPANY OF NEW HAMPSHIRE AND SUBSIDIARIES CONSOLIDATED BALANCE SHEETS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>100210023 - Statement - PUBLIC SERVICE COMPANY OF NEW HAMPSHIRE AND SUBSIDIARIES CONSOLIDATED BALANCE SHEETS (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/PUBLICSERVICECOMPANYOFNEWHAMPSHIREANDSUBSIDIARIESCONSOLIDATEDBALANCESHEETSParenthetical</Role>
      <ShortName>PUBLIC SERVICE COMPANY OF NEW HAMPSHIRE AND SUBSIDIARIES CONSOLIDATED BALANCE SHEETS (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>100220024 - Statement - PUBLIC SERVICE COMPANY OF NEW HAMPSHIRE AND SUBSIDIARIES CONSOLIDATED STATEMENTS OF INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/PUBLICSERVICECOMPANYOFNEWHAMPSHIREANDSUBSIDIARIESCONSOLIDATEDSTATEMENTSOFINCOME</Role>
      <ShortName>PUBLIC SERVICE COMPANY OF NEW HAMPSHIRE AND SUBSIDIARIES CONSOLIDATED STATEMENTS OF INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>100230025 - Statement - PUBLIC SERVICE COMPANY OF NEW HAMPSHIRE AND SUBSIDIARIES CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/PUBLICSERVICECOMPANYOFNEWHAMPSHIREANDSUBSIDIARIESCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOME</Role>
      <ShortName>PUBLIC SERVICE COMPANY OF NEW HAMPSHIRE AND SUBSIDIARIES CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>100240026 - Statement - PUBLIC SERVICE COMPANY OF NEW HAMPSHIRE AND SUBSIDIARIES CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDER'S EQUITY</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/PUBLICSERVICECOMPANYOFNEWHAMPSHIREANDSUBSIDIARIESCONSOLIDATEDSTATEMENTSOFCOMMONSTOCKHOLDERSEQUITY</Role>
      <ShortName>PUBLIC SERVICE COMPANY OF NEW HAMPSHIRE AND SUBSIDIARIES CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDER'S EQUITY</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>100250027 - Statement - PUBLIC SERVICE COMPANY OF NEW HAMPSHIRE AND SUBSIDIARIES CONSOLIDATED STATEMENTS OF CASH FLOWS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/PUBLICSERVICECOMPANYOFNEWHAMPSHIREANDSUBSIDIARIESCONSOLIDATEDSTATEMENTSOFCASHFLOWS</Role>
      <ShortName>PUBLIC SERVICE COMPANY OF NEW HAMPSHIRE AND SUBSIDIARIES CONSOLIDATED STATEMENTS OF CASH FLOWS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>210011001 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIES</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>210141002 - Disclosure - REGULATORY ACCOUNTING</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/REGULATORYACCOUNTING</Role>
      <ShortName>REGULATORY ACCOUNTING</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>210191003 - Disclosure - PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/PROPERTYPLANTANDEQUIPMENTANDACCUMULATEDDEPRECIATION</Role>
      <ShortName>PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>30</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>210251004 - Disclosure - DERIVATIVE INSTRUMENTS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/DERIVATIVEINSTRUMENTS</Role>
      <ShortName>DERIVATIVE INSTRUMENTS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>31</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>210311005 - Disclosure - MARKETABLE SECURITIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/MARKETABLESECURITIES</Role>
      <ShortName>MARKETABLE SECURITIES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>32</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>210371006 - Disclosure - INVESTMENTS IN UNCONSOLIDATED AFFILIATES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/INVESTMENTSINUNCONSOLIDATEDAFFILIATES</Role>
      <ShortName>INVESTMENTS IN UNCONSOLIDATED AFFILIATES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>33</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>210411007 - Disclosure - ASSET RETIREMENT OBLIGATIONS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/ASSETRETIREMENTOBLIGATIONS</Role>
      <ShortName>ASSET RETIREMENT OBLIGATIONS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>210451008 - Disclosure - SHORT-TERM DEBT</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SHORTTERMDEBT</Role>
      <ShortName>SHORT-TERM DEBT</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>210491009 - Disclosure - LONG-TERM DEBT</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/LONGTERMDEBT</Role>
      <ShortName>LONG-TERM DEBT</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>210551010 - Disclosure - RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/RATEREDUCTIONBONDSANDVARIABLEINTERESTENTITIES</Role>
      <ShortName>RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>210611011 - Disclosure - EMPLOYEE BENEFITS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EMPLOYEEBENEFITS</Role>
      <ShortName>EMPLOYEE BENEFITS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>210791012 - Disclosure - INCOME TAXES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/INCOMETAXES</Role>
      <ShortName>INCOME TAXES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>210871013 - Disclosure - COMMITMENTS AND CONTINGENCIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COMMITMENTSANDCONTINGENCIES</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>211021014 - Disclosure - LEASES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/LEASES</Role>
      <ShortName>LEASES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>211091015 - Disclosure - FAIR VALUE OF FINANCIAL INSTRUMENTS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/FAIRVALUEOFFINANCIALINSTRUMENTS</Role>
      <ShortName>FAIR VALUE OF FINANCIAL INSTRUMENTS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>211121016 - Disclosure - ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/ACCUMULATEDOTHERCOMPREHENSIVEINCOMELOSS</Role>
      <ShortName>ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>211171017 - Disclosure - DIVIDEND RESTRICTIONS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/DIVIDENDRESTRICTIONS</Role>
      <ShortName>DIVIDEND RESTRICTIONS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>211191018 - Disclosure - COMMON SHARES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COMMONSHARES</Role>
      <ShortName>COMMON SHARES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>211231019 - Disclosure - PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/PREFERREDSTOCKNOTSUBJECTTOMANDATORYREDEMPTION</Role>
      <ShortName>PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>211271020 - Disclosure - COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COMMONSHAREHOLDERSEQUITYANDNONCONTROLLINGINTERESTS</Role>
      <ShortName>COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>211291021 - Disclosure - EARNINGS PER SHARE</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EARNINGSPERSHARE</Role>
      <ShortName>EARNINGS PER SHARE</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>211331022 - Disclosure - REVENUES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/REVENUES</Role>
      <ShortName>REVENUES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>211371023 - Disclosure - SEGMENT INFORMATION</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SEGMENTINFORMATION</Role>
      <ShortName>SEGMENT INFORMATION</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>211411024 - Disclosure - ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/ACQUISITIONOFASSETSOFCOLUMBIAGASOFMASSACHUSETTS</Role>
      <ShortName>ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>211461025 - Disclosure - GOODWILL</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/GOODWILL</Role>
      <ShortName>GOODWILL</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>211501026 - Disclosure - SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SCHEDULEIFINANCIALINFORMATIONOFREGISTRANT</Role>
      <ShortName>SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>211551027 - Disclosure - SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SCHEDULEIIVALUATIONANDQUALIFYINGACCOUNTSANDRESERVES</Role>
      <ShortName>SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>220022001 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESPolicies</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>230033001 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESTables</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIES</ParentRole>
      <Position>56</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>230153002 - Disclosure - REGULATORY ACCOUNTING (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/REGULATORYACCOUNTINGTables</Role>
      <ShortName>REGULATORY ACCOUNTING (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/REGULATORYACCOUNTING</ParentRole>
      <Position>57</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>230203003 - Disclosure - PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/PROPERTYPLANTANDEQUIPMENTANDACCUMULATEDDEPRECIATIONTables</Role>
      <ShortName>PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/PROPERTYPLANTANDEQUIPMENTANDACCUMULATEDDEPRECIATION</ParentRole>
      <Position>58</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>230263004 - Disclosure - DERIVATIVE INSTRUMENTS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/DERIVATIVEINSTRUMENTSTables</Role>
      <ShortName>DERIVATIVE INSTRUMENTS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/DERIVATIVEINSTRUMENTS</ParentRole>
      <Position>59</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>230323005 - Disclosure - MARKETABLE SECURITIES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/MARKETABLESECURITIESTables</Role>
      <ShortName>MARKETABLE SECURITIES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/MARKETABLESECURITIES</ParentRole>
      <Position>60</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>230383006 - Disclosure - INVESTMENTS IN UNCONSOLIDATED AFFILIATES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/INVESTMENTSINUNCONSOLIDATEDAFFILIATESTables</Role>
      <ShortName>INVESTMENTS IN UNCONSOLIDATED AFFILIATES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/INVESTMENTSINUNCONSOLIDATEDAFFILIATES</ParentRole>
      <Position>61</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>230423007 - Disclosure - ASSET RETIREMENT OBLIGATIONS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/ASSETRETIREMENTOBLIGATIONSTables</Role>
      <ShortName>ASSET RETIREMENT OBLIGATIONS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/ASSETRETIREMENTOBLIGATIONS</ParentRole>
      <Position>62</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>230463008 - Disclosure - SHORT-TERM DEBT (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SHORTTERMDEBTTables</Role>
      <ShortName>SHORT-TERM DEBT (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/SHORTTERMDEBT</ParentRole>
      <Position>63</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>230503009 - Disclosure - LONG-TERM DEBT (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/LONGTERMDEBTTables</Role>
      <ShortName>LONG-TERM DEBT (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/LONGTERMDEBT</ParentRole>
      <Position>64</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>230563010 - Disclosure - RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/RATEREDUCTIONBONDSANDVARIABLEINTERESTENTITIESTables</Role>
      <ShortName>RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/RATEREDUCTIONBONDSANDVARIABLEINTERESTENTITIES</ParentRole>
      <Position>65</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>230623011 - Disclosure - EMPLOYEE BENEFITS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EMPLOYEEBENEFITSTables</Role>
      <ShortName>EMPLOYEE BENEFITS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/EMPLOYEEBENEFITS</ParentRole>
      <Position>66</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>230803012 - Disclosure - INCOME TAXES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/INCOMETAXESTables</Role>
      <ShortName>INCOME TAXES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/INCOMETAXES</ParentRole>
      <Position>67</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>230883013 - Disclosure - COMMITMENTS AND CONTINGENCIES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COMMITMENTSANDCONTINGENCIESTables</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/COMMITMENTSANDCONTINGENCIES</ParentRole>
      <Position>68</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>231033014 - Disclosure - LEASES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/LEASESTables</Role>
      <ShortName>LEASES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/LEASES</ParentRole>
      <Position>69</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>231103015 - Disclosure - FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/FAIRVALUEOFFINANCIALINSTRUMENTSTables</Role>
      <ShortName>FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/FAIRVALUEOFFINANCIALINSTRUMENTS</ParentRole>
      <Position>70</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>231133016 - Disclosure - ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/ACCUMULATEDOTHERCOMPREHENSIVEINCOMELOSSTables</Role>
      <ShortName>ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/ACCUMULATEDOTHERCOMPREHENSIVEINCOMELOSS</ParentRole>
      <Position>71</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>231203017 - Disclosure - COMMON SHARES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COMMONSHARESTables</Role>
      <ShortName>COMMON SHARES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/COMMONSHARES</ParentRole>
      <Position>72</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>231243018 - Disclosure - PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/PREFERREDSTOCKNOTSUBJECTTOMANDATORYREDEMPTIONTables</Role>
      <ShortName>PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/PREFERREDSTOCKNOTSUBJECTTOMANDATORYREDEMPTION</ParentRole>
      <Position>73</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>231303019 - Disclosure - EARNINGS PER SHARE (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EARNINGSPERSHARETables</Role>
      <ShortName>EARNINGS PER SHARE (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/EARNINGSPERSHARE</ParentRole>
      <Position>74</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>231343020 - Disclosure - REVENUES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/REVENUESTables</Role>
      <ShortName>REVENUES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/REVENUES</ParentRole>
      <Position>75</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>231383021 - Disclosure - SEGMENT INFORMATION (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SEGMENTINFORMATIONTables</Role>
      <ShortName>SEGMENT INFORMATION (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/SEGMENTINFORMATION</ParentRole>
      <Position>76</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>231423022 - Disclosure - ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/ACQUISITIONOFASSETSOFCOLUMBIAGASOFMASSACHUSETTSTables</Role>
      <ShortName>ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/ACQUISITIONOFASSETSOFCOLUMBIAGASOFMASSACHUSETTS</ParentRole>
      <Position>77</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>231473023 - Disclosure - GOODWILL (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/GOODWILLTables</Role>
      <ShortName>GOODWILL (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.eversource.com/role/GOODWILL</ParentRole>
      <Position>78</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>240044001 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESNarrativeDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>79</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>240054002 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Allowance for Uncollectible Accounts (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESAllowanceforUncollectibleAccountsDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Allowance for Uncollectible Accounts (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>80</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>240064003 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES -Transfer of Energy Efficiency Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESTransferofEnergyEfficiencyLoansDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES -Transfer of Energy Efficiency Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>81</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>240074004 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Fuel, Materials, Supplies and Inventory (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESFuelMaterialsSuppliesandInventoryDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Fuel, Materials, Supplies and Inventory (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>82</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>240084005 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Operating Expenses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofOperatingExpensesDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Operating Expenses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>83</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R84.htm</HtmlFileName>
      <LongName>240094006 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of AFUDC and Weighted Average AFUDC (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofAFUDCandWeightedAverageAFUDCDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of AFUDC and Weighted Average AFUDC (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>84</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R85.htm</HtmlFileName>
      <LongName>240104007 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Other Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESOtherIncomeDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Other Income (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>85</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R86.htm</HtmlFileName>
      <LongName>240114008 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Other Taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofOtherTaxesDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Other Taxes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>86</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R87.htm</HtmlFileName>
      <LongName>240124009 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Supplemental Cash Flow Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESSupplementalCashFlowInformationDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Supplemental Cash Flow Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>87</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R88.htm</HtmlFileName>
      <LongName>240134010 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Cash and Cash Equivalents (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofCashandCashEquivalentsDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Cash and Cash Equivalents (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>88</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R89.htm</HtmlFileName>
      <LongName>240164011 - Disclosure - REGULATORY ACCOUNTING - Components of Regulatory Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/REGULATORYACCOUNTINGComponentsofRegulatoryAssetsDetails</Role>
      <ShortName>REGULATORY ACCOUNTING - Components of Regulatory Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>89</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R90.htm</HtmlFileName>
      <LongName>240174012 - Disclosure - REGULATORY ACCOUNTING - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/REGULATORYACCOUNTINGNarrativeDetails</Role>
      <ShortName>REGULATORY ACCOUNTING - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>90</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R91.htm</HtmlFileName>
      <LongName>240184013 - Disclosure - REGULATORY ACCOUNTING - Components of Regulatory Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/REGULATORYACCOUNTINGComponentsofRegulatoryLiabilitiesDetails</Role>
      <ShortName>REGULATORY ACCOUNTING - Components of Regulatory Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>91</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R92.htm</HtmlFileName>
      <LongName>240214014 - Disclosure - PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Investment in Utility Property, Plant and Equipment By Asset (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/PROPERTYPLANTANDEQUIPMENTANDACCUMULATEDDEPRECIATIONInvestmentinUtilityPropertyPlantandEquipmentByAssetDetails</Role>
      <ShortName>PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Investment in Utility Property, Plant and Equipment By Asset (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>92</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R93.htm</HtmlFileName>
      <LongName>240224015 - Disclosure - PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION -Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/PROPERTYPLANTANDEQUIPMENTANDACCUMULATEDDEPRECIATIONNarrativeDetails</Role>
      <ShortName>PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION -Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.eversource.com/role/PROPERTYPLANTANDEQUIPMENTANDACCUMULATEDDEPRECIATIONTables</ParentRole>
      <Position>93</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R94.htm</HtmlFileName>
      <LongName>240234016 - Disclosure - PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Schedule of Aggregate Composite Depreciation Rates (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/PROPERTYPLANTANDEQUIPMENTANDACCUMULATEDDEPRECIATIONScheduleofAggregateCompositeDepreciationRatesDetails</Role>
      <ShortName>PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Schedule of Aggregate Composite Depreciation Rates (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>94</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R95.htm</HtmlFileName>
      <LongName>240244017 - Disclosure - PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Schedule of Average Remaining Useful Lives of Depreciable Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/PROPERTYPLANTANDEQUIPMENTANDACCUMULATEDDEPRECIATIONScheduleofAverageRemainingUsefulLivesofDepreciableAssetsDetails</Role>
      <ShortName>PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Schedule of Average Remaining Useful Lives of Depreciable Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>95</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R96.htm</HtmlFileName>
      <LongName>240274018 - Disclosure - DERIVATIVE INSTRUMENTS - Schedule of Gross Fair Value of Contracts (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/DERIVATIVEINSTRUMENTSScheduleofGrossFairValueofContractsDetails</Role>
      <ShortName>DERIVATIVE INSTRUMENTS - Schedule of Gross Fair Value of Contracts (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>96</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R97.htm</HtmlFileName>
      <LongName>240284019 - Disclosure - DERIVATIVE INSTRUMENTS - Derivative Contracts at Fair Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/DERIVATIVEINSTRUMENTSDerivativeContractsatFairValueDetails</Role>
      <ShortName>DERIVATIVE INSTRUMENTS - Derivative Contracts at Fair Value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>97</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R98.htm</HtmlFileName>
      <LongName>240294020 - Disclosure - DERIVATIVE INSTRUMENTS - Unobservable Inputs Utilized (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/DERIVATIVEINSTRUMENTSUnobservableInputsUtilizedDetails</Role>
      <ShortName>DERIVATIVE INSTRUMENTS - Unobservable Inputs Utilized (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>98</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R99.htm</HtmlFileName>
      <LongName>240304021 - Disclosure - DERIVATIVE INSTRUMENTS - Variations Using Significant unobservable Inputs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/DERIVATIVEINSTRUMENTSVariationsUsingSignificantunobservableInputsDetails</Role>
      <ShortName>DERIVATIVE INSTRUMENTS - Variations Using Significant unobservable Inputs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>99</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R100.htm</HtmlFileName>
      <LongName>240334022 - Disclosure - MARKETABLE SECURITIES - Equity Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/MARKETABLESECURITIESEquitySecuritiesDetails</Role>
      <ShortName>MARKETABLE SECURITIES - Equity Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>100</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R101.htm</HtmlFileName>
      <LongName>240344023 - Disclosure - MARKETABLE SECURITIES - Available-for-Sale Debt Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/MARKETABLESECURITIESAvailableforSaleDebtSecuritiesDetails</Role>
      <ShortName>MARKETABLE SECURITIES - Available-for-Sale Debt Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>101</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R102.htm</HtmlFileName>
      <LongName>240354024 - Disclosure - MARKETABLE SECURITIES - Contractual Maturity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/MARKETABLESECURITIESContractualMaturityDetails</Role>
      <ShortName>MARKETABLE SECURITIES - Contractual Maturity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>102</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R103.htm</HtmlFileName>
      <LongName>240364025 - Disclosure - MARKETABLE SECURITIES - Fair Value Measurement (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/MARKETABLESECURITIESFairValueMeasurementDetails</Role>
      <ShortName>MARKETABLE SECURITIES - Fair Value Measurement (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>103</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R104.htm</HtmlFileName>
      <LongName>240394026 - Disclosure - INVESTMENTS IN UNCONSOLIDATED AFFILIATES - Summary of Investments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/INVESTMENTSINUNCONSOLIDATEDAFFILIATESSummaryofInvestmentsDetails</Role>
      <ShortName>INVESTMENTS IN UNCONSOLIDATED AFFILIATES - Summary of Investments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>104</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R105.htm</HtmlFileName>
      <LongName>240404027 - Disclosure - INVESTMENTS IN UNCONSOLIDATED AFFILIATES - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/INVESTMENTSINUNCONSOLIDATEDAFFILIATESNarrativeDetails</Role>
      <ShortName>INVESTMENTS IN UNCONSOLIDATED AFFILIATES - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>105</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R106.htm</HtmlFileName>
      <LongName>240434028 - Disclosure - ASSET RETIREMENT OBLIGATIONS - Schedule of Reconciliation of Beginning and Ending Balance (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/ASSETRETIREMENTOBLIGATIONSScheduleofReconciliationofBeginningandEndingBalanceDetails</Role>
      <ShortName>ASSET RETIREMENT OBLIGATIONS - Schedule of Reconciliation of Beginning and Ending Balance (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>106</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R107.htm</HtmlFileName>
      <LongName>240444029 - Disclosure - ASSET RETIREMENT OBLIGATIONS - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/ASSETRETIREMENTOBLIGATIONSNarrativeDetails</Role>
      <ShortName>ASSET RETIREMENT OBLIGATIONS - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>107</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R108.htm</HtmlFileName>
      <LongName>240474030 - Disclosure - SHORT-TERM DEBT - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SHORTTERMDEBTNarrativeDetails</Role>
      <ShortName>SHORT-TERM DEBT - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>108</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R109.htm</HtmlFileName>
      <LongName>240484031 - Disclosure - SHORT-TERM DEBT - Schedule of Debt (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SHORTTERMDEBTScheduleofDebtDetails</Role>
      <ShortName>SHORT-TERM DEBT - Schedule of Debt (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>109</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R110.htm</HtmlFileName>
      <LongName>240514032 - Disclosure - LONG-TERM DEBT - Schedule of Long-Term Debt Outstanding (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/LONGTERMDEBTScheduleofLongTermDebtOutstandingDetails</Role>
      <ShortName>LONG-TERM DEBT - Schedule of Long-Term Debt Outstanding (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>110</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R111.htm</HtmlFileName>
      <LongName>240524033 - Disclosure - LONG-TERM DEBT - Schedule of Issuances and Repayments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/LONGTERMDEBTScheduleofIssuancesandRepaymentsDetails</Role>
      <ShortName>LONG-TERM DEBT - Schedule of Issuances and Repayments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>111</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R112.htm</HtmlFileName>
      <LongName>240534034 - Disclosure - LONG-TERM DEBT - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/LONGTERMDEBTNarrativeDetails</Role>
      <ShortName>LONG-TERM DEBT - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>112</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R113.htm</HtmlFileName>
      <LongName>240544035 - Disclosure - LONG-TERM DEBT - Schedule of Long-term Debt Maturities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/LONGTERMDEBTScheduleofLongtermDebtMaturitiesDetails</Role>
      <ShortName>LONG-TERM DEBT - Schedule of Long-term Debt Maturities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>113</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R114.htm</HtmlFileName>
      <LongName>240574036 - Disclosure - RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/RATEREDUCTIONBONDSANDVARIABLEINTERESTENTITIESNarrativeDetails</Role>
      <ShortName>RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.eversource.com/role/RATEREDUCTIONBONDSANDVARIABLEINTERESTENTITIESTables</ParentRole>
      <Position>114</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R115.htm</HtmlFileName>
      <LongName>240584037 - Disclosure - RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Balance Sheet (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/RATEREDUCTIONBONDSANDVARIABLEINTERESTENTITIESBalanceSheetDetails</Role>
      <ShortName>RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Balance Sheet (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>115</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R116.htm</HtmlFileName>
      <LongName>240594038 - Disclosure - RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Income Statement (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/RATEREDUCTIONBONDSANDVARIABLEINTERESTENTITIESIncomeStatementDetails</Role>
      <ShortName>RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Income Statement (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>116</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R117.htm</HtmlFileName>
      <LongName>240604039 - Disclosure - RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES- Rate Reduction Bonds, Principal and Interest Payments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/RATEREDUCTIONBONDSANDVARIABLEINTERESTENTITIESRateReductionBondsPrincipalandInterestPaymentsDetails</Role>
      <ShortName>RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES- Rate Reduction Bonds, Principal and Interest Payments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>117</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R118.htm</HtmlFileName>
      <LongName>240634040 - Disclosure - EMPLOYEE BENEFITS - Schedule of Pension Benefit Obligations (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EMPLOYEEBENEFITSScheduleofPensionBenefitObligationsDetails</Role>
      <ShortName>EMPLOYEE BENEFITS - Schedule of Pension Benefit Obligations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>118</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R119.htm</HtmlFileName>
      <LongName>240644041 - Disclosure - EMPLOYEE BENEFITS - Pension Plan Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EMPLOYEEBENEFITSPensionPlanNarrativeDetails</Role>
      <ShortName>EMPLOYEE BENEFITS - Pension Plan Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>119</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R120.htm</HtmlFileName>
      <LongName>240654042 - Disclosure - EMPLOYEE BENEFITS - Schedule of Funded Status (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EMPLOYEEBENEFITSScheduleofFundedStatusDetails</Role>
      <ShortName>EMPLOYEE BENEFITS - Schedule of Funded Status (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>120</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R121.htm</HtmlFileName>
      <LongName>240664043 - Disclosure - EMPLOYEE BENEFITS - Schedule of Actuarial Assumptions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EMPLOYEEBENEFITSScheduleofActuarialAssumptionsDetails</Role>
      <ShortName>EMPLOYEE BENEFITS - Schedule of Actuarial Assumptions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>121</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R122.htm</HtmlFileName>
      <LongName>240674044 - Disclosure - EMPLOYEE BENEFITS - Schedule of Components of Net Periodic Benefit Costs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EMPLOYEEBENEFITSScheduleofComponentsofNetPeriodicBenefitCostsDetails</Role>
      <ShortName>EMPLOYEE BENEFITS - Schedule of Components of Net Periodic Benefit Costs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>122</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R123.htm</HtmlFileName>
      <LongName>240684045 - Disclosure - EMPLOYEE BENEFITS - Schedule of Assumptions used To Calculate Pension and SERP and PBOP (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EMPLOYEEBENEFITSScheduleofAssumptionsusedToCalculatePensionandSERPandPBOPDetails</Role>
      <ShortName>EMPLOYEE BENEFITS - Schedule of Assumptions used To Calculate Pension and SERP and PBOP (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>123</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R124.htm</HtmlFileName>
      <LongName>240694046 - Disclosure - EMPLOYEE BENEFITS - Summary of Changes in Plan Assets and Benefit Obligations (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EMPLOYEEBENEFITSSummaryofChangesinPlanAssetsandBenefitObligationsDetails</Role>
      <ShortName>EMPLOYEE BENEFITS - Summary of Changes in Plan Assets and Benefit Obligations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>124</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R125.htm</HtmlFileName>
      <LongName>240704047 - Disclosure - EMPLOYEE BENEFITS - Schedule of Estimated Future Benefit Payments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EMPLOYEEBENEFITSScheduleofEstimatedFutureBenefitPaymentsDetails</Role>
      <ShortName>EMPLOYEE BENEFITS - Schedule of Estimated Future Benefit Payments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>125</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R126.htm</HtmlFileName>
      <LongName>240714048 - Disclosure - EMPLOYEE BENEFITS - Schedule of Long-term Rates of Return on Pension and PBOP (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EMPLOYEEBENEFITSScheduleofLongtermRatesofReturnonPensionandPBOPDetails</Role>
      <ShortName>EMPLOYEE BENEFITS - Schedule of Long-term Rates of Return on Pension and PBOP (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>126</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R127.htm</HtmlFileName>
      <LongName>240724049 - Disclosure - EMPLOYEE BENEFITS - Schedule of Asset Category (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EMPLOYEEBENEFITSScheduleofAssetCategoryDetails</Role>
      <ShortName>EMPLOYEE BENEFITS - Schedule of Asset Category (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>127</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R128.htm</HtmlFileName>
      <LongName>240734050 - Disclosure - EMPLOYEE BENEFITS - Defined Contribution Plan Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EMPLOYEEBENEFITSDefinedContributionPlanNarrativeDetails</Role>
      <ShortName>EMPLOYEE BENEFITS - Defined Contribution Plan Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>128</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R129.htm</HtmlFileName>
      <LongName>240744051 - Disclosure - EMPLOYEE BENEFITS - Schedule of Defined Contribution Plans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EMPLOYEEBENEFITSScheduleofDefinedContributionPlansDetails</Role>
      <ShortName>EMPLOYEE BENEFITS - Schedule of Defined Contribution Plans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>129</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R130.htm</HtmlFileName>
      <LongName>240754052 - Disclosure - EMPLOYEE BENEFITS - Share-Based Payments Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EMPLOYEEBENEFITSShareBasedPaymentsNarrativeDetails</Role>
      <ShortName>EMPLOYEE BENEFITS - Share-Based Payments Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>130</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R131.htm</HtmlFileName>
      <LongName>240764053 - Disclosure - EMPLOYEE BENEFITS - Summary of RSU and Share Transactions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EMPLOYEEBENEFITSSummaryofRSUandShareTransactionsDetails</Role>
      <ShortName>EMPLOYEE BENEFITS - Summary of RSU and Share Transactions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>131</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R132.htm</HtmlFileName>
      <LongName>240774054 - Disclosure - EMPLOYEE BENEFITS - Schedule of Compensation Expense and Income Tax Benefit (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EMPLOYEEBENEFITSScheduleofCompensationExpenseandIncomeTaxBenefitDetails</Role>
      <ShortName>EMPLOYEE BENEFITS - Schedule of Compensation Expense and Income Tax Benefit (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>132</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R133.htm</HtmlFileName>
      <LongName>240784055 - Disclosure - EMPLOYEE BENEFITS - Schedule of Other Retirement Benefits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EMPLOYEEBENEFITSScheduleofOtherRetirementBenefitsDetails</Role>
      <ShortName>EMPLOYEE BENEFITS - Schedule of Other Retirement Benefits (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>133</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R134.htm</HtmlFileName>
      <LongName>240814056 - Disclosure - INCOME TAXES - Components of Income Tax Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/INCOMETAXESComponentsofIncomeTaxExpenseDetails</Role>
      <ShortName>INCOME TAXES - Components of Income Tax Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>134</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R135.htm</HtmlFileName>
      <LongName>240824057 - Disclosure - INCOME TAXES - Reconciliation Between Income Tax Expense and Expected Tax Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/INCOMETAXESReconciliationBetweenIncomeTaxExpenseandExpectedTaxExpenseDetails</Role>
      <ShortName>INCOME TAXES - Reconciliation Between Income Tax Expense and Expected Tax Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>135</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R136.htm</HtmlFileName>
      <LongName>240834058 - Disclosure - INCOME TAXES - Temporary Differences That Give Rise To Accumulated Deferred Income Tax Obligations (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/INCOMETAXESTemporaryDifferencesThatGiveRiseToAccumulatedDeferredIncomeTaxObligationsDetails</Role>
      <ShortName>INCOME TAXES - Temporary Differences That Give Rise To Accumulated Deferred Income Tax Obligations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>136</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R137.htm</HtmlFileName>
      <LongName>240844059 - Disclosure - INCOME TAXES - Tax Credits and Loss Carryforwards (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/INCOMETAXESTaxCreditsandLossCarryforwardsDetails</Role>
      <ShortName>INCOME TAXES - Tax Credits and Loss Carryforwards (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>137</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R138.htm</HtmlFileName>
      <LongName>240854060 - Disclosure - INCOME TAXES - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/INCOMETAXESNarrativeDetails</Role>
      <ShortName>INCOME TAXES - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>138</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R139.htm</HtmlFileName>
      <LongName>240864061 - Disclosure - INCOME TAXES - Reconciliation of Unrecognized Tax Benefit (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/INCOMETAXESReconciliationofUnrecognizedTaxBenefitDetails</Role>
      <ShortName>INCOME TAXES - Reconciliation of Unrecognized Tax Benefit (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>139</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R140.htm</HtmlFileName>
      <LongName>240894062 - Disclosure - COMMITMENTS AND CONTINGENCIES - Schedule of Reconciliation of Activity in Environmental Reserve (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COMMITMENTSANDCONTINGENCIESScheduleofReconciliationofActivityinEnvironmentalReserveDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - Schedule of Reconciliation of Activity in Environmental Reserve (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>140</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R141.htm</HtmlFileName>
      <LongName>240904063 - Disclosure - COMMITMENTS AND CONTINGENCIES - Schedule of Number of Sites and Reserves (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COMMITMENTSANDCONTINGENCIESScheduleofNumberofSitesandReservesDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - Schedule of Number of Sites and Reserves (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>141</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R142.htm</HtmlFileName>
      <LongName>240914064 - Disclosure - COMMITMENTS AND CONTINGENCIES - Environmental Matters Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COMMITMENTSANDCONTINGENCIESEnvironmentalMattersNarrativeDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - Environmental Matters Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>142</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R143.htm</HtmlFileName>
      <LongName>240924065 - Disclosure - COMMITMENTS AND CONTINGENCIES - Schedule of Estimated Future Annual Costs of Long term Contractual Agreement (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COMMITMENTSANDCONTINGENCIESScheduleofEstimatedFutureAnnualCostsofLongtermContractualAgreementDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - Schedule of Estimated Future Annual Costs of Long term Contractual Agreement (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>143</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R144.htm</HtmlFileName>
      <LongName>240934066 - Disclosure - COMMITMENTS AND CONTINGENCIES - Long-Term Contractual Arrangement Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COMMITMENTSANDCONTINGENCIESLongTermContractualArrangementNarrativeDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - Long-Term Contractual Arrangement Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>144</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R145.htm</HtmlFileName>
      <LongName>240944067 - Disclosure - COMMITMENTS AND CONTINGENCIES - Schedule of Total Costs Incurred (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COMMITMENTSANDCONTINGENCIESScheduleofTotalCostsIncurredDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - Schedule of Total Costs Incurred (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>145</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R146.htm</HtmlFileName>
      <LongName>240954068 - Disclosure - COMMITMENTS AND CONTINGENCIES - Spent Nuclear Fuel Obligations Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COMMITMENTSANDCONTINGENCIESSpentNuclearFuelObligationsNarrativeDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - Spent Nuclear Fuel Obligations Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>146</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R147.htm</HtmlFileName>
      <LongName>240964069 - Disclosure - COMMITMENTS AND CONTINGENCIES - Schedule of Guarantees and Indemnifications (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COMMITMENTSANDCONTINGENCIESScheduleofGuaranteesandIndemnificationsDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - Schedule of Guarantees and Indemnifications (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>147</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R148.htm</HtmlFileName>
      <LongName>240974070 - Disclosure - COMMITMENTS AND CONTINGENCIES - Guarantees and Obligations Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COMMITMENTSANDCONTINGENCIESGuaranteesandObligationsNarrativeDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - Guarantees and Obligations Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>148</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R149.htm</HtmlFileName>
      <LongName>240984071 - Disclosure - COMMITMENTS AND CONTINGENCIES - FERC ROE Complaints (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COMMITMENTSANDCONTINGENCIESFERCROEComplaintsDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - FERC ROE Complaints (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>149</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R150.htm</HtmlFileName>
      <LongName>240994072 - Disclosure - COMMITMENTS AND CONTINGENCIES - Eversource and NSTAR Electric Boston Harbor Civil Action (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COMMITMENTSANDCONTINGENCIESEversourceandNSTARElectricBostonHarborCivilActionDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - Eversource and NSTAR Electric Boston Harbor Civil Action (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>150</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R151.htm</HtmlFileName>
      <LongName>241004073 - Disclosure - COMMITMENTS AND CONTINGENCIES - CL&amp;P Tropical Storm Isaias Response Investigation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COMMITMENTSANDCONTINGENCIESCLPTropicalStormIsaiasResponseInvestigationDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - CL&amp;P Tropical Storm Isaias Response Investigation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>151</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R152.htm</HtmlFileName>
      <LongName>241014074 - Disclosure - COMMITMENTS AND CONTINGENCIES - CL&amp;P Comprehensive Settlement Agreement (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COMMITMENTSANDCONTINGENCIESCLPComprehensiveSettlementAgreementDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - CL&amp;P Comprehensive Settlement Agreement (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>152</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R153.htm</HtmlFileName>
      <LongName>241044075 - Disclosure - LEASES - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/LEASESNarrativeDetails</Role>
      <ShortName>LEASES - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>153</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R154.htm</HtmlFileName>
      <LongName>241054076 - Disclosure - LEASES - Components of Lease Cost (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/LEASESComponentsofLeaseCostDetails</Role>
      <ShortName>LEASES - Components of Lease Cost (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>154</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R155.htm</HtmlFileName>
      <LongName>241064077 - Disclosure - LEASES - Supplemental Balance Sheet Information Related to Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/LEASESSupplementalBalanceSheetInformationRelatedtoLeasesDetails</Role>
      <ShortName>LEASES - Supplemental Balance Sheet Information Related to Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>155</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R156.htm</HtmlFileName>
      <LongName>241074078 - Disclosure - LEASES - Other Information Related to Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/LEASESOtherInformationRelatedtoLeasesDetails</Role>
      <ShortName>LEASES - Other Information Related to Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>156</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R157.htm</HtmlFileName>
      <LongName>241084079 - Disclosure - LEASES - Future Minimum Lease Payments under Long-Term Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/LEASESFutureMinimumLeasePaymentsunderLongTermLeasesDetails</Role>
      <ShortName>LEASES - Future Minimum Lease Payments under Long-Term Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>157</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R158.htm</HtmlFileName>
      <LongName>241114080 - Disclosure - FAIR VALUE OF FINANCIAL INSTRUMENTS - Fair Value Hierarchy (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/FAIRVALUEOFFINANCIALINSTRUMENTSFairValueHierarchyDetails</Role>
      <ShortName>FAIR VALUE OF FINANCIAL INSTRUMENTS - Fair Value Hierarchy (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>158</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R159.htm</HtmlFileName>
      <LongName>241144081 - Disclosure - ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) - Schedule of Changes in AOCI By Component (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/ACCUMULATEDOTHERCOMPREHENSIVEINCOMELOSSScheduleofChangesinAOCIByComponentDetails</Role>
      <ShortName>ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) - Schedule of Changes in AOCI By Component (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>159</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R160.htm</HtmlFileName>
      <LongName>241154082 - Disclosure - ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/ACCUMULATEDOTHERCOMPREHENSIVEINCOMELOSSNarrativeDetails</Role>
      <ShortName>ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>160</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R161.htm</HtmlFileName>
      <LongName>241164083 - Disclosure - ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) - Schedule of Amounts Reclassified From AOCI By Component (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/ACCUMULATEDOTHERCOMPREHENSIVEINCOMELOSSScheduleofAmountsReclassifiedFromAOCIByComponentDetails</Role>
      <ShortName>ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) - Schedule of Amounts Reclassified From AOCI By Component (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>161</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R162.htm</HtmlFileName>
      <LongName>241184084 - Disclosure - DIVIDEND RESTRICTIONS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/DIVIDENDRESTRICTIONSDetails</Role>
      <ShortName>DIVIDEND RESTRICTIONS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.eversource.com/role/DIVIDENDRESTRICTIONS</ParentRole>
      <Position>162</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R163.htm</HtmlFileName>
      <LongName>241214085 - Disclosure - COMMON SHARES - Common Shares Authorized and Issued (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COMMONSHARESCommonSharesAuthorizedandIssuedDetails</Role>
      <ShortName>COMMON SHARES - Common Shares Authorized and Issued (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>163</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R164.htm</HtmlFileName>
      <LongName>241224086 - Disclosure - COMMON SHARES - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COMMONSHARESNarrativeDetails</Role>
      <ShortName>COMMON SHARES - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>164</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R165.htm</HtmlFileName>
      <LongName>241254087 - Disclosure - PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/PREFERREDSTOCKNOTSUBJECTTOMANDATORYREDEMPTIONNarrativeDetails</Role>
      <ShortName>PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.eversource.com/role/PREFERREDSTOCKNOTSUBJECTTOMANDATORYREDEMPTIONTables</ParentRole>
      <Position>165</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R166.htm</HtmlFileName>
      <LongName>241264088 - Disclosure - PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION - Schedule of Preferred Stock by Class (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/PREFERREDSTOCKNOTSUBJECTTOMANDATORYREDEMPTIONScheduleofPreferredStockbyClassDetails</Role>
      <ShortName>PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION - Schedule of Preferred Stock by Class (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>166</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R167.htm</HtmlFileName>
      <LongName>241284089 - Disclosure - COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/COMMONSHAREHOLDERSEQUITYANDNONCONTROLLINGINTERESTSDetails</Role>
      <ShortName>COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.eversource.com/role/COMMONSHAREHOLDERSEQUITYANDNONCONTROLLINGINTERESTS</ParentRole>
      <Position>167</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R168.htm</HtmlFileName>
      <LongName>241314090 - Disclosure - EARNINGS PER SHARE - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EARNINGSPERSHARENarrativeDetails</Role>
      <ShortName>EARNINGS PER SHARE - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>168</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R169.htm</HtmlFileName>
      <LongName>241324091 - Disclosure - EARNINGS PER SHARE - Components of Basic and Diluted EPS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/EARNINGSPERSHAREComponentsofBasicandDilutedEPSDetails</Role>
      <ShortName>EARNINGS PER SHARE - Components of Basic and Diluted EPS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>169</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R170.htm</HtmlFileName>
      <LongName>241354092 - Disclosure - REVENUES - Operating Revenues Disaggregated by Revenue Source (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/REVENUESOperatingRevenuesDisaggregatedbyRevenueSourceDetails</Role>
      <ShortName>REVENUES - Operating Revenues Disaggregated by Revenue Source (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>170</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R171.htm</HtmlFileName>
      <LongName>241364093 - Disclosure - REVENUES - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/REVENUESNarrativeDetails</Role>
      <ShortName>REVENUES - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>171</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R172.htm</HtmlFileName>
      <LongName>241394094 - Disclosure - SEGMENT INFORMATION - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SEGMENTINFORMATIONNarrativeDetails</Role>
      <ShortName>SEGMENT INFORMATION - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>172</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R173.htm</HtmlFileName>
      <LongName>241404095 - Disclosure - SEGMENT INFORMATION - Schedule of Segment Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SEGMENTINFORMATIONScheduleofSegmentInformationDetails</Role>
      <ShortName>SEGMENT INFORMATION - Schedule of Segment Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>173</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R174.htm</HtmlFileName>
      <LongName>241434096 - Disclosure - ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/ACQUISITIONOFASSETSOFCOLUMBIAGASOFMASSACHUSETTSNarrativeDetails</Role>
      <ShortName>ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.eversource.com/role/ACQUISITIONOFASSETSOFCOLUMBIAGASOFMASSACHUSETTSTables</ParentRole>
      <Position>174</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R175.htm</HtmlFileName>
      <LongName>241444097 - Disclosure - ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS - Preliminary Allocation of the Cash Purchase Price (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/ACQUISITIONOFASSETSOFCOLUMBIAGASOFMASSACHUSETTSPreliminaryAllocationoftheCashPurchasePriceDetails</Role>
      <ShortName>ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS - Preliminary Allocation of the Cash Purchase Price (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>175</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R176.htm</HtmlFileName>
      <LongName>241454098 - Disclosure - ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS - Schedule of Pro Forma Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/ACQUISITIONOFASSETSOFCOLUMBIAGASOFMASSACHUSETTSScheduleofProFormaInformationDetails</Role>
      <ShortName>ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS - Schedule of Pro Forma Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>176</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R177.htm</HtmlFileName>
      <LongName>241484099 - Disclosure - GOODWILL - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/GOODWILLNarrativeDetails</Role>
      <ShortName>GOODWILL - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>177</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R178.htm</HtmlFileName>
      <LongName>241494100 - Disclosure - GOODWILL - Summary of Goodwill by Reportable Segment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/GOODWILLSummaryofGoodwillbyReportableSegmentDetails</Role>
      <ShortName>GOODWILL - Summary of Goodwill by Reportable Segment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>178</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R179.htm</HtmlFileName>
      <LongName>241514101 - Disclosure - SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - BALANCE SHEET (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SCHEDULEIFINANCIALINFORMATIONOFREGISTRANTBALANCESHEETDetails</Role>
      <ShortName>SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - BALANCE SHEET (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>179</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R180.htm</HtmlFileName>
      <LongName>241524102 - Disclosure - SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - STATEMENTS OF INCOME (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SCHEDULEIFINANCIALINFORMATIONOFREGISTRANTSTATEMENTSOFINCOMEDetails</Role>
      <ShortName>SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - STATEMENTS OF INCOME (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>180</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R181.htm</HtmlFileName>
      <LongName>241534103 - Disclosure - SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - STATEMENTS OF COMPREHENSIVE INCOME (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SCHEDULEIFINANCIALINFORMATIONOFREGISTRANTSTATEMENTSOFCOMPREHENSIVEINCOMEDetails</Role>
      <ShortName>SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - STATEMENTS OF COMPREHENSIVE INCOME (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>181</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R182.htm</HtmlFileName>
      <LongName>241544104 - Disclosure - SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - STATEMENT OF CASH FLOW (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SCHEDULEIFINANCIALINFORMATIONOFREGISTRANTSTATEMENTOFCASHFLOWDetails</Role>
      <ShortName>SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - STATEMENT OF CASH FLOW (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>182</Position>
    </Report>
    <Report instance="es-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R183.htm</HtmlFileName>
      <LongName>241564105 - Disclosure - SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.eversource.com/role/SCHEDULEIIVALUATIONANDQUALIFYINGACCOUNTSANDRESERVESDetails</Role>
      <ShortName>SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.eversource.com/role/SCHEDULEIIVALUATIONANDQUALIFYINGACCOUNTSANDRESERVES</ParentRole>
      <Position>183</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File doctype="10-K" original="es-20211231.htm">es-20211231.htm</File>
    <File>a2021-ex21subsidiariesofth.htm</File>
    <File>a202110k-ex102xtrusteecomp.htm</File>
    <File>a202110k-ex311eversource.htm</File>
    <File>a202110k-ex31eversource.htm</File>
    <File>a202110k-ex32eversource.htm</File>
    <File>a202110k-exhibit23consents.htm</File>
    <File>a202110k-exhibit311clp.htm</File>
    <File>a202110k-exhibit311nste.htm</File>
    <File>a202110k-exhibit311psnh.htm</File>
    <File>a202110k-exhibit31clp.htm</File>
    <File>a202110k-exhibit31nste.htm</File>
    <File>a202110k-exhibit31psnh.htm</File>
    <File>a202110k-exhibit32clp.htm</File>
    <File>a202110k-exhibit32nste.htm</File>
    <File>a202110k-exhibit32psnh.htm</File>
    <File>es-20211231.xsd</File>
    <File>es-20211231_cal.xml</File>
    <File>es-20211231_def.xml</File>
    <File>es-20211231_lab.xml</File>
    <File>es-20211231_pre.xml</File>
    <File>exhibit1012eversourcecredi.htm</File>
    <File>exhibit1013nstarcreditagre.htm</File>
  </InputFiles>
  <SupplementalFiles>
    <File>es-20211231_g1.jpg</File>
    <File>es-20211231_g10.jpg</File>
    <File>es-20211231_g2.jpg</File>
    <File>es-20211231_g3.jpg</File>
    <File>es-20211231_g4.jpg</File>
    <File>es-20211231_g5.jpg</File>
    <File>es-20211231_g6.jpg</File>
    <File>es-20211231_g7.jpg</File>
    <File>es-20211231_g8.jpg</File>
    <File>es-20211231_g9.jpg</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy items="1">http://fasb.org/srt/2021-01-31</BaseTaxonomy>
    <BaseTaxonomy items="5171">http://fasb.org/us-gaap/2021-01-31</BaseTaxonomy>
    <BaseTaxonomy items="104">http://xbrl.sec.gov/dei/2021q4</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
