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Fair Value of Derivative and Other Financial Instruments - Recurring (Details) (USD $) In Thousands, unless otherwise specified | Mar. 31, 2015 | Dec. 31, 2014
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PNMR and PNM [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | $ 257,464 us-gaap_AvailableForSaleSecurities / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | $ 250,145 us-gaap_AvailableForSaleSecurities / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
PNM Resources [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Long-term debt | 2,322,072 us-gaap_LongTermDebtFairValue / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 2,173,117 us-gaap_LongTermDebtFairValue / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Investment In PVNGS lessor notes | 17,173 pnm_InvestmentInLessorNotesFairValueDisclosure / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 32,836 pnm_InvestmentInLessorNotesFairValueDisclosure / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Other investments | 1,135 pnm_OtherInvestmentsFairValueDisclosure / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 2,375 pnm_OtherInvestmentsFairValueDisclosure / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
PNM Resources [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Long-term debt | 0 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Investment In PVNGS lessor notes | 0 pnm_InvestmentInLessorNotesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 pnm_InvestmentInLessorNotesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Other investments | 509 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 639 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
PNM Resources [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Long-term debt | 2,322,072 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 2,173,117 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Investment In PVNGS lessor notes | 0 pnm_InvestmentInLessorNotesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 pnm_InvestmentInLessorNotesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Other investments | 0 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
PNM Resources [Member] | Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Long-term debt | 0 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 0 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Investment In PVNGS lessor notes | 17,173 pnm_InvestmentInLessorNotesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 32,836 pnm_InvestmentInLessorNotesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Other investments | 626 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 1,736 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Public Service Company of New Mexico [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Long-term debt | 1,627,751 us-gaap_LongTermDebtFairValue / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 1,624,222 us-gaap_LongTermDebtFairValue / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Investment In PVNGS lessor notes | 17,173 pnm_InvestmentInLessorNotesFairValueDisclosure / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 32,836 pnm_InvestmentInLessorNotesFairValueDisclosure / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Other investments | 267 pnm_OtherInvestmentsFairValueDisclosure / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 397 pnm_OtherInvestmentsFairValueDisclosure / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Public Service Company of New Mexico [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Long-term debt | 0 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 0 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Investment In PVNGS lessor notes | 0 pnm_InvestmentInLessorNotesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 0 pnm_InvestmentInLessorNotesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Other investments | 267 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 397 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Public Service Company of New Mexico [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Long-term debt | 1,627,751 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 1,624,222 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Investment In PVNGS lessor notes | 0 pnm_InvestmentInLessorNotesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 0 pnm_InvestmentInLessorNotesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Other investments | 0 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 0 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Public Service Company of New Mexico [Member] | Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Long-term debt | 0 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 0 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Investment In PVNGS lessor notes | 17,173 pnm_InvestmentInLessorNotesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 32,836 pnm_InvestmentInLessorNotesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Other investments | 0 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 0 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Texas-New Mexico Power Company [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Long-term debt | 427,356 us-gaap_LongTermDebtFairValue / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | 427,356 us-gaap_LongTermDebtFairValue / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Other investments | 242 pnm_OtherInvestmentsFairValueDisclosure / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | 242 pnm_OtherInvestmentsFairValueDisclosure / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Texas-New Mexico Power Company [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Long-term debt | 0 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | 0 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Other investments | 242 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | 242 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Texas-New Mexico Power Company [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Long-term debt | 427,356 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | 427,356 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Other investments | 0 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | 0 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Texas-New Mexico Power Company [Member] | Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Long-term debt | 0 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | 0 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Other investments | 0 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | 0 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Reported Value Measurement [Member] | PNM Resources [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Long-term debt | 2,125,007 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 1,975,090 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Investment In PVNGS lessor notes | 16,806 pnm_InvestmentInLessorNotesFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 31,232 pnm_InvestmentInLessorNotesFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Other investments | 509 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 1,762 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Reported Value Measurement [Member] | Public Service Company of New Mexico [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Long-term debt | 1,490,666 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 1,490,657 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Investment In PVNGS lessor notes | 16,806 pnm_InvestmentInLessorNotesFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 31,232 pnm_InvestmentInLessorNotesFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Other investments | 267 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 397 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Reported Value Measurement [Member] | Texas-New Mexico Power Company [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Long-term debt | 365,575 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | 365,667 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Other investments | 242 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | 242 pnm_OtherInvestmentsFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Cash and equivalents [Member] | PNMR and PNM [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 5,142 us-gaap_AvailableForSaleSecurities / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CashAndCashEquivalentsMember | 8,276 us-gaap_AvailableForSaleSecurities / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CashAndCashEquivalentsMember
Domestic value [Member] | PNMR and PNM [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 46,129 us-gaap_AvailableForSaleSecurities / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_DomesticValueMember | 45,340 us-gaap_AvailableForSaleSecurities / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_DomesticValueMember
Domestic growth [Member] | PNMR and PNM [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 78,013 us-gaap_AvailableForSaleSecurities / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_DomesticGrowthMember | 74,053 us-gaap_AvailableForSaleSecurities / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_DomesticGrowthMember
International and other [Member] | PNMR and PNM [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 17,478 us-gaap_AvailableForSaleSecurities / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_MultinationalMember | 16,599 us-gaap_AvailableForSaleSecurities / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_MultinationalMember
U.S. Government [Member] | PNMR and PNM [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 21,912 us-gaap_AvailableForSaleSecurities / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember | 22,563 us-gaap_AvailableForSaleSecurities / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember
Municipals [Member] | PNMR and PNM [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 73,554 us-gaap_AvailableForSaleSecurities / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MunicipalBondsMember | 68,973 us-gaap_AvailableForSaleSecurities / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MunicipalBondsMember
Corporate and other [Member] | PNMR and PNM [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 15,236 us-gaap_AvailableForSaleSecurities / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_OtherDebtSecuritiesMember | 14,341 us-gaap_AvailableForSaleSecurities / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_OtherDebtSecuritiesMember
Fair Value, Measurements, Recurring [Member] | PNMR and PNM [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 257,464 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | 250,145 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Fair Value, Measurements, Recurring [Member] | PNMR and PNM [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 172,266 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | 169,919 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Fair Value, Measurements, Recurring [Member] | PNMR and PNM [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 85,198 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | 80,226 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Fair Value, Measurements, Recurring [Member] | Commodity Contract [Member] | PNMR and PNM [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Commodity derivative instruments, Assets | 9,342 us-gaap_DerivativeAssets / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | 11,232 us-gaap_DerivativeAssets / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Commodity derivative instruments, Liabilities | (1,512)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | (1,686)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Commodity derivative instruments, Net | 7,830 us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | 9,546 us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Fair Value, Measurements, Recurring [Member] | Commodity Contract [Member] | PNMR and PNM [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Commodity derivative instruments, Assets | 0 us-gaap_DerivativeAssets / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | 0 us-gaap_DerivativeAssets / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Commodity derivative instruments, Liabilities | 0 us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | 0 us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Commodity derivative instruments, Net | 0 us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | 0 us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Fair Value, Measurements, Recurring [Member] | Commodity Contract [Member] | PNMR and PNM [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Commodity derivative instruments, Assets | 9,342 us-gaap_DerivativeAssets / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | 11,232 us-gaap_DerivativeAssets / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Commodity derivative instruments, Liabilities | (1,512)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | (1,686)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Commodity derivative instruments, Net | 7,830 us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | 9,546 us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Fair Value, Measurements, Recurring [Member] | Cash and equivalents [Member] | PNMR and PNM [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 5,142 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CashAndCashEquivalentsMember | 8,276 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CashAndCashEquivalentsMember
Fair Value, Measurements, Recurring [Member] | Cash and equivalents [Member] | PNMR and PNM [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 5,142 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CashAndCashEquivalentsMember | 8,276 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CashAndCashEquivalentsMember
Fair Value, Measurements, Recurring [Member] | Cash and equivalents [Member] | PNMR and PNM [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CashAndCashEquivalentsMember | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CashAndCashEquivalentsMember
Fair Value, Measurements, Recurring [Member] | Domestic value [Member] | PNMR and PNM [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 46,129 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_DomesticValueMember | 45,340 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_DomesticValueMember
Fair Value, Measurements, Recurring [Member] | Domestic value [Member] | PNMR and PNM [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 46,129 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_DomesticValueMember | 45,340 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_DomesticValueMember
Fair Value, Measurements, Recurring [Member] | Domestic value [Member] | PNMR and PNM [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_DomesticValueMember | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_DomesticValueMember
Fair Value, Measurements, Recurring [Member] | Domestic growth [Member] | PNMR and PNM [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 78,013 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_DomesticGrowthMember | 74,053 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_DomesticGrowthMember
Fair Value, Measurements, Recurring [Member] | Domestic growth [Member] | PNMR and PNM [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 78,013 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_DomesticGrowthMember | 74,053 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_DomesticGrowthMember
Fair Value, Measurements, Recurring [Member] | Domestic growth [Member] | PNMR and PNM [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_DomesticGrowthMember | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_DomesticGrowthMember
Fair Value, Measurements, Recurring [Member] | International and other [Member] | PNMR and PNM [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 17,478 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_MultinationalMember | 16,599 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_MultinationalMember
Fair Value, Measurements, Recurring [Member] | International and other [Member] | PNMR and PNM [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 17,478 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_MultinationalMember | 16,599 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_MultinationalMember
Fair Value, Measurements, Recurring [Member] | International and other [Member] | PNMR and PNM [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_MultinationalMember | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = pnm_MultinationalMember
Fair Value, Measurements, Recurring [Member] | U.S. Government [Member] | PNMR and PNM [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 21,912 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember | 22,563 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember
Fair Value, Measurements, Recurring [Member] | U.S. Government [Member] | PNMR and PNM [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 20,603 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember | 20,808 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember
Fair Value, Measurements, Recurring [Member] | U.S. Government [Member] | PNMR and PNM [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 1,309 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember | 1,755 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember
Fair Value, Measurements, Recurring [Member] | Municipals [Member] | PNMR and PNM [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 73,554 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MunicipalBondsMember | 68,973 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MunicipalBondsMember
Fair Value, Measurements, Recurring [Member] | Municipals [Member] | PNMR and PNM [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MunicipalBondsMember | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MunicipalBondsMember
Fair Value, Measurements, Recurring [Member] | Municipals [Member] | PNMR and PNM [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 73,554 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MunicipalBondsMember | 68,973 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MunicipalBondsMember
Fair Value, Measurements, Recurring [Member] | Corporate and other [Member] | PNMR and PNM [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 15,236 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_OtherDebtSecuritiesMember | 14,341 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_OtherDebtSecuritiesMember
Fair Value, Measurements, Recurring [Member] | Corporate and other [Member] | PNMR and PNM [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | 4,901 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_OtherDebtSecuritiesMember | 4,843 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_OtherDebtSecuritiesMember
Fair Value, Measurements, Recurring [Member] | Corporate and other [Member] | PNMR and PNM [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments | $ 10,335 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_OtherDebtSecuritiesMember | $ 9,498 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_OtherDebtSecuritiesMember

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