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Commitments and Contingencies - Stipulation Filed with the NMPRC (Details) (USD $) In Millions, unless otherwise specified | 0 Months Ended |  |  |
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Apr. 08, 2015 | Oct. 01, 2014 | Dec. 20, 2013 | Mar. 31, 2015 MW | Jan. 15, 2015 MW | Jun. 26, 2014 MW
San Juan Generating Station Unit 4 [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |
Public Utilities, Additional Ownership To Be Obtained, in Megawatts |  | 132 pnm_PublicUtilitiesAdditionalOwnershipToBeObtainedinMegawatts / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 78 pnm_PublicUtilitiesAdditionalOwnershipToBeObtainedinMegawatts / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 132 pnm_PublicUtilitiesAdditionalOwnershipToBeObtainedinMegawatts / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  | 132 pnm_PublicUtilitiesAdditionalOwnershipToBeObtainedinMegawatts / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Public Utilities, Estimated rate base value at 1/1/2018 |  | $ 26.0 pnm_PublicUtilitiesEstimatedratebasevalueat112018 / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |
Public Utilities, Ownership in Megawatts PNM has agreed not to obtain |  |  |  |  | 65 pnm_PublicUtilitiesOwnershipinMegawattsPNMhasagreednottoobtain / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |
San Juan Generating Station Unit 4 [Member] | Subsequent Event [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR Hearing Examiner Recommended Denial [Member] |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |
Public Utilities, Additional Ownership To Be Obtained, in Megawatts | 132 pnm_PublicUtilitiesAdditionalOwnershipToBeObtainedinMegawatts / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSNCRHearingExaminerRecommendedDenialMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |
Period of time to accept or reject modifications in recommendation | 7 days |  |  |  |  |
San Juan Generating Station Unit 3 [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |
Public Utilities, Proposed reduction in carrying value |  | 26 pnm_PublicUtilitiesProposedreductionincarryingvalue / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |
Public Utilities,Estimated unrecoverable increase in operations and maintenance |  | 20 pnm_PublicUtilitiesEstimatedunrecoverableincreaseinoperationsandmaintenance / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |
San Juan Generating Station Unit 3 [Member] | Maximum [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |
Public Utilities,Estimated pre-tax regulatory disallowance |  | 70 pnm_PublicUtilitiesEstimatedpretaxregulatorydisallowance / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |  |
San Juan Generating Station Unit 3 [Member] | Minimum [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |
Public Utilities,Estimated pre-tax regulatory disallowance |  | 60 pnm_PublicUtilitiesEstimatedpretaxregulatorydisallowance / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RangeAxis = us-gaap_MinimumMember |  |  |  |
San Juan Generating Station Unit 3 [Member] | Subsequent Event [Member] | Maximum [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |
Public Utilities,Estimated pre-tax regulatory disallowance | 155 pnm_PublicUtilitiesEstimatedpretaxregulatorydisallowance / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |
San Juan Generating Station Unit 3 [Member] | Subsequent Event [Member] | Minimum [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |
Public Utilities,Estimated pre-tax regulatory disallowance | 145 pnm_PublicUtilitiesEstimatedpretaxregulatorydisallowance / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |
San Juan Generating Station Units 2 and 3 [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |
Net book value |  |  |  | 280 pnm_NetBookValue / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnits2And3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |
San Juan Generating Station Units 2 and 3 [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |
Public Utilities, Recovery Percentage of Estimated undepreciated value at 12/31/17 |  | 50.00%pnm_PublicUtilitiesRecoveryPercentageofEstimatedundepreciatedvalueat123117 / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnits2And3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |
Public Utilities, Estimated undepreciated value at 12/31/17 |  | 231.0 pnm_PublicUtilitiesEstimatedundepreciatedvalueat123117 / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnits2And3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |
Public Utilities, Requested Time Period to Recover Retired Units NBV |  | 20 years | 20 years |  |  |
Public Utilities, Write-off Percentage of Estimated undepreciated value at 12/31/17 |  | 50.00%pnm_PublicUtilitiesWriteoffPercentageofEstimatedundepreciatedvalueat123117 / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnits2And3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |
San Juan Generating Station Units 2 and 3 [Member] | Subsequent Event [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |
Public Utilities, Estimated undepreciated value at 12/31/17 | 128.5 pnm_PublicUtilitiesEstimatedundepreciatedvalueat123117 / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnits2And3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |
Public Utilities, Write-off Percentage of Estimated undepreciated value at 12/31/17 | 50.00%pnm_PublicUtilitiesWriteoffPercentageofEstimatedundepreciatedvalueat123117 / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnits2And3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |
Palo Verde Nuclear Generating Station Unit 3 [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |
Net book value |  |  |  | 145 pnm_NetBookValue / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |
Palo Verde Nuclear Generating Station Unit 3 [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |
Public Utilities, Estimated rate base value at 1/1/2018 |  | 221.1 pnm_PublicUtilitiesEstimatedratebasevalueat112018 / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |
Public Utilities, Proposed value per Kilowatt effective January 1, 2018 |  | 1,650 pnm_PublicUtilitiesProposedvalueperKilowatteffectiveJanuary12018 / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |
Palo Verde Nuclear Generating Station Unit 3 [Member] | PNMR and PNM [Member] |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |
Public Utilities, Number of Megawatts Nuclear Generation |  |  |  | 134 pnm_PublicUtilitiesNumberofMegawattsNuclearGeneration / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PnmrAndPnmMember |  |
Palo Verde Nuclear Generating Station Unit 3 [Member] | PNMR and PNM [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |
Public Utilities, Number of Megawatts Nuclear Generation |  | 134 pnm_PublicUtilitiesNumberofMegawattsNuclearGeneration / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | 134 pnm_PublicUtilitiesNumberofMegawattsNuclearGeneration / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PnmrAndPnmMember |  |  |
Public Utilities, Proposed value per Kilowatt effective January 1, 2018 |  |  | 2,500 pnm_PublicUtilitiesProposedvalueperKilowatteffectiveJanuary12018 / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PnmrAndPnmMember |  |  |
Public Utilities, Percentage capacity factor 7-year performance threshold |  | 75.00%pnm_PublicUtilitiesPercentagecapacityfactor7yearperformancethreshold / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PnmrAndPnmMember |  |  |  |
Public Utilities, Period over which to measure capacity performance |  | 7 years |  |  |  |
Palo Verde Nuclear Generating Station Unit 3 [Member] | Subsequent Event [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR Hearing Examiner Recommended Denial [Member] |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |
Public Utilities, Estimated rate base value at 1/1/2018 | 143.5 pnm_PublicUtilitiesEstimatedratebasevalueat112018 / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSNCRHearingExaminerRecommendedDenialMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |
Public Utilities, Proposed value per Kilowatt effective January 1, 2018 | 1,071 pnm_PublicUtilitiesProposedvalueperKilowatteffectiveJanuary12018 / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSNCRHearingExaminerRecommendedDenialMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |
San Juan Generating Station Units 1 and 4 [Member] | Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Maximum [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |
Estimated Installation Capital Costs |  | $ 90.6 pnm_EstimatedInstallationCapitalCosts / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnits1And4Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_PublicUtilitiesCommitmentsAndContingenciesByNatureOfExpenseAxis = pnm_InstallationCostsIncludingConstructionManagementGrossReceiptsTaxesAfudcAndOtherPnmCostsMember / us-gaap_RangeAxis = us-gaap_MaximumMember | 82.0 pnm_EstimatedInstallationCapitalCosts / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnits1And4Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_PublicUtilitiesCommitmentsAndContingenciesByNatureOfExpenseAxis = pnm_InstallationCostsIncludingConstructionManagementGrossReceiptsTaxesAfudcAndOtherPnmCostsMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |

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