<?xml version='1.0' encoding='UTF-8'?>
<FilingSummary>
  <Version>3.8.0.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>633</ContextCount>
  <ElementCount>556</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>211</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>35</UnitCount>
  <MyReports>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0001000 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/DocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>1001000 - Statement - Condensed Consolidated Statements of Earnings</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/CondensedConsolidatedStatementsOfEarnings</Role>
      <ShortName>Condensed Consolidated Statements of Earnings</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>1002000 - Statement - Condensed Consolidated Statements of Comprehensive Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/CondensedConsolidatedStatementsOfComprehensiveIncome</Role>
      <ShortName>Condensed Consolidated Statements of Comprehensive Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>1002001 - Statement - Condensed Consolidated Statements of Comprehensive Income (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/CondensedConsolidatedStatementsOfComprehensiveIncomeParenthetical</Role>
      <ShortName>Condensed Consolidated Statements of Comprehensive Income (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>1003000 - Statement - Condensed Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/CondensedConsolidatedStatementsOfCashFlows</Role>
      <ShortName>Condensed Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>1004000 - Statement - Condensed Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/CondensedConsolidatedBalanceSheets</Role>
      <ShortName>Condensed Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>1004501 - Statement - Condensed Consolidated Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/CondensedConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>Condensed Consolidated Balance Sheets (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>1005000 - Statement - Condensed Consolidated Statement of Changes in Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/CondensedConsolidatedStatementOfChangesInEquity</Role>
      <ShortName>Condensed Consolidated Statement of Changes in Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>2101100 - Disclosure - Significant Accounting Policies and Responsibility for Financial Statements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/SignificantAccountingPoliciesAndResponsibilityForFinancialStatements</Role>
      <ShortName>Significant Accounting Policies and Responsibility for Financial Statements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>2102100 - Disclosure - Earnings Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/EarningsPerShare</Role>
      <ShortName>Earnings Per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>2103100 - Disclosure - Segment Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/SegmentInformation</Role>
      <ShortName>Segment Information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>2104100 - Disclosure - Accumulated Other Comprehensive Income (Loss)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/AccumulatedOtherComprehensiveIncomeLoss</Role>
      <ShortName>Accumulated Other Comprehensive Income (Loss)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>2105100 - Disclosure - Variable Interest Entities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/VariableInterestEntities</Role>
      <ShortName>Variable Interest Entities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>2106100 - Disclosure - Lease Commitments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/LeaseCommitments</Role>
      <ShortName>Lease Commitments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>2107100 - Disclosure - Fair Value of Derivative and Other Financial Instruments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/FairValueOfDerivativeAndOtherFinancialInstruments</Role>
      <ShortName>Fair Value of Derivative and Other Financial Instruments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>2108100 - Disclosure - Stock-Based Compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/StockBasedCompensation</Role>
      <ShortName>Stock-Based Compensation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>2109100 - Disclosure - Financing</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/Financing</Role>
      <ShortName>Financing</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>2110100 - Disclosure - Pension and Other Postretirement Benefit Plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/PensionAndOtherPostretirementBenefitPlans</Role>
      <ShortName>Pension and Other Postretirement Benefit Plans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>2112100 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/CommitmentsAndContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>2118100 - Disclosure - Regulatory and Rate Matters</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/RegulatoryAndRateMatters</Role>
      <ShortName>Regulatory and Rate Matters</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>2119100 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/IncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>2120100 - Disclosure - Related Party Transactions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/RelatedPartyTransactions</Role>
      <ShortName>Related Party Transactions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>2121100 - Disclosure - Goodwill</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/Goodwill</Role>
      <ShortName>Goodwill</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>2201201 - Disclosure - Significant Accounting Policies and Responsibility for Financial Statements (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/SignificantAccountingPoliciesAndResponsibilityForFinancialStatementsPolicies</Role>
      <ShortName>Significant Accounting Policies and Responsibility for Financial Statements (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/SignificantAccountingPoliciesAndResponsibilityForFinancialStatements</ParentRole>
      <Position>24</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>2302301 - Disclosure - Earnings Per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/EarningsPerShareTables</Role>
      <ShortName>Earnings Per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/EarningsPerShare</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>2303301 - Disclosure - Segment Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/SegmentInformationTables</Role>
      <ShortName>Segment Information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/SegmentInformation</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>2304301 - Disclosure - Accumulated Other Comprehensive Income (Loss) (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/AccumulatedOtherComprehensiveIncomeLossTables</Role>
      <ShortName>Accumulated Other Comprehensive Income (Loss) (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/AccumulatedOtherComprehensiveIncomeLoss</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>2305301 - Disclosure - Variable Interest Entities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/VariableInterestEntitiesTables</Role>
      <ShortName>Variable Interest Entities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/VariableInterestEntities</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>2307301 - Disclosure - Fair Value of Derivative and Other Financial Instruments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/FairValueOfDerivativeAndOtherFinancialInstrumentsTables</Role>
      <ShortName>Fair Value of Derivative and Other Financial Instruments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/FairValueOfDerivativeAndOtherFinancialInstruments</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>2308301 - Disclosure - Stock-Based Compensation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/StockBasedCompensationTables</Role>
      <ShortName>Stock-Based Compensation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/StockBasedCompensation</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>2309301 - Disclosure - Financing (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/FinancingTables</Role>
      <ShortName>Financing (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/Financing</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>2310301 - Disclosure - Pension and Other Postretirement Benefit Plans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/PensionAndOtherPostretirementBenefitPlansTables</Role>
      <ShortName>Pension and Other Postretirement Benefit Plans (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/PensionAndOtherPostretirementBenefitPlans</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>2318301 - Disclosure - Regulatory and Rate Matters (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/RegulatoryAndRateMattersTables</Role>
      <ShortName>Regulatory and Rate Matters (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/RegulatoryAndRateMatters</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>2320301 - Disclosure - Related Party Transactions (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/RelatedPartyTransactionsTables</Role>
      <ShortName>Related Party Transactions (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/RelatedPartyTransactions</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>2401402 - Disclosure - Significant Accounting Policies and Responsibility for Financial Statements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/SignificantAccountingPoliciesAndResponsibilityForFinancialStatementsDetails</Role>
      <ShortName>Significant Accounting Policies and Responsibility for Financial Statements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/SignificantAccountingPoliciesAndResponsibilityForFinancialStatementsPolicies</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>2402402 - Disclosure - Earnings Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/EarningsPerShareDetails</Role>
      <ShortName>Earnings Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/EarningsPerShareTables</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>2403402 - Disclosure - Segment Information - Summarized Financial Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/SegmentInformationSummarizedFinancialInformationDetails</Role>
      <ShortName>Segment Information - Summarized Financial Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>2404402 - Disclosure - Accumulated Other Comprehensive Income (Loss) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/AccumulatedOtherComprehensiveIncomeLossDetails</Role>
      <ShortName>Accumulated Other Comprehensive Income (Loss) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/AccumulatedOtherComprehensiveIncomeLossTables</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>2405402 - Disclosure - Variable Interest Entities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/VariableInterestEntitiesDetails</Role>
      <ShortName>Variable Interest Entities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/VariableInterestEntitiesTables</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>2406401 - Disclosure - Lease Commitments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/LeaseCommitmentsDetails</Role>
      <ShortName>Lease Commitments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/LeaseCommitments</ParentRole>
      <Position>40</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>2407402 - Disclosure - Fair Value of Derivative and Other Financial Instruments - Overview and Commodity Derivatives (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/FairValueOfDerivativeAndOtherFinancialInstrumentsOverviewAndCommodityDerivativesDetails</Role>
      <ShortName>Fair Value of Derivative and Other Financial Instruments - Overview and Commodity Derivatives (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>2407403 - Disclosure - Fair Value of Derivative and Other Financial Instruments - Statement of Earnings Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/FairValueOfDerivativeAndOtherFinancialInstrumentsStatementOfEarningsInformationDetails</Role>
      <ShortName>Fair Value of Derivative and Other Financial Instruments - Statement of Earnings Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>2407404 - Disclosure - Fair Value of Derivative and Other Financial Instruments - Margin, Notional Amounts and Credit Rating (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/FairValueOfDerivativeAndOtherFinancialInstrumentsMarginNotionalAmountsAndCreditRatingDetails</Role>
      <ShortName>Fair Value of Derivative and Other Financial Instruments - Margin, Notional Amounts and Credit Rating (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>2407405 - Disclosure - Fair Value of Derivative and Other Financial Instruments - Sale of Power (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/FairValueOfDerivativeAndOtherFinancialInstrumentsSaleOfPowerDetails</Role>
      <ShortName>Fair Value of Derivative and Other Financial Instruments - Sale of Power (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>2407406 - Disclosure - Fair Value of Derivative and Other Financial Instruments - Available for Sale Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/FairValueOfDerivativeAndOtherFinancialInstrumentsAvailableForSaleSecuritiesDetails</Role>
      <ShortName>Fair Value of Derivative and Other Financial Instruments - Available for Sale Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>2407407 - Disclosure - Fair Value of Derivative and Other Financial Instruments - Maturities of Debt Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/FairValueOfDerivativeAndOtherFinancialInstrumentsMaturitiesOfDebtSecuritiesDetails</Role>
      <ShortName>Fair Value of Derivative and Other Financial Instruments - Maturities of Debt Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>2407408 - Disclosure - Fair Value of Derivative and Other Financial Instruments - Items Recorded and Presented by Level of Hierarchy (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/FairValueOfDerivativeAndOtherFinancialInstrumentsItemsRecordedAndPresentedByLevelOfHierarchyDetails</Role>
      <ShortName>Fair Value of Derivative and Other Financial Instruments - Items Recorded and Presented by Level of Hierarchy (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>2408402 - Disclosure - Stock-Based Compensation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/StockBasedCompensationDetails</Role>
      <ShortName>Stock-Based Compensation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/StockBasedCompensationTables</ParentRole>
      <Position>48</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>2409402 - Disclosure - Financing - Financing Activities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/FinancingFinancingActivitiesDetails</Role>
      <ShortName>Financing - Financing Activities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>2409403 - Disclosure - Financing - Short-term Debt and Liquidity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/FinancingShortTermDebtAndLiquidityDetails</Role>
      <ShortName>Financing - Short-term Debt and Liquidity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>2410402 - Disclosure - Pension and Other Postretirement Benefit Plans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/PensionAndOtherPostretirementBenefitPlansDetails</Role>
      <ShortName>Pension and Other Postretirement Benefit Plans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/PensionAndOtherPostretirementBenefitPlansTables</ParentRole>
      <Position>51</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>2412401 - Disclosure - Commitments and Contingencies - Nuclear Spent Fuel and Waste Disposal (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/CommitmentsAndContingenciesNuclearSpentFuelAndWasteDisposalDetails</Role>
      <ShortName>Commitments and Contingencies - Nuclear Spent Fuel and Waste Disposal (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>2412402 - Disclosure - Commitments and Contingencies - The Clean Air Act (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/CommitmentsAndContingenciesCleanAirActDetails</Role>
      <ShortName>Commitments and Contingencies - The Clean Air Act (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>2412403 - Disclosure - Commitments and Contingencies - Coal Supply (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/CommitmentsAndContingenciesCoalSupplyDetails</Role>
      <ShortName>Commitments and Contingencies - Coal Supply (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>2412404 - Disclosure - Commitments and Contingencies - Royalty Rates, Tax Assessment, Insurance and Other Matters (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/CommitmentsAndContingenciesRoyaltyRatesTaxAssessmentInsuranceAndOtherMattersDetails</Role>
      <ShortName>Commitments and Contingencies - Royalty Rates, Tax Assessment, Insurance and Other Matters (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>2418402 - Disclosure - Regulatory and Rate Matters - PNM (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/RegulatoryAndRateMattersPnmDetails</Role>
      <ShortName>Regulatory and Rate Matters - PNM (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/RegulatoryAndRateMattersTables</ParentRole>
      <Position>56</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>2418403 - Disclosure - Regulatory and Rate Matters - TNMP Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/RegulatoryAndRateMattersTnmpNarrativeDetails</Role>
      <ShortName>Regulatory and Rate Matters - TNMP Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>2418404 - Disclosure - Regulatory and Rate Matters - Transmission Cost of Service Rates (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/RegulatoryAndRateMattersTransmissionCostOfServiceRatesDetails</Role>
      <ShortName>Regulatory and Rate Matters - Transmission Cost of Service Rates (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>2419401 - Disclosure - Income Taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/IncomeTaxesDetails</Role>
      <ShortName>Income Taxes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/IncomeTaxes</ParentRole>
      <Position>59</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>2420402 - Disclosure - Related Party Transactions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/RelatedPartyTransactionsDetails</Role>
      <ShortName>Related Party Transactions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/RelatedPartyTransactionsTables</ParentRole>
      <Position>60</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>2421401 - Disclosure - Goodwill (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.pnmresources.com/role/GoodwillDetails</Role>
      <ShortName>Goodwill (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.pnmresources.com/role/Goodwill</ParentRole>
      <Position>61</Position>
    </Report>
    <Report instance="pnm-20170930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9999.htm</HtmlFileName>
      <LongName>Uncategorized Items - pnm-20170930.xml</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/role/uncategorizedFacts</Role>
      <ShortName>Uncategorized Items - pnm-20170930.xml</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>pnm-20170930.xml</File>
    <File>pnm-20170930.xsd</File>
    <File>pnm-20170930_cal.xml</File>
    <File>pnm-20170930_def.xml</File>
    <File>pnm-20170930_lab.xml</File>
    <File>pnm-20170930_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://fasb.org/us-gaap/2017-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2014-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
