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Commitments and Contingencies - The Clean Air Act (Details) (USD $) In Millions, unless otherwise specified | 0 Months Ended |  |  |
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Oct. 01, 2014 | Dec. 20, 2013 MW | Mar. 31, 2015 state | Oct. 31, 2012 | Jun. 26, 2014 MW
Clean Air Act related to Regional Haze [Member] |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |
Public Utilities, Number of States To Address Regional Haze |  |  | 50 pnm_PublicUtilitiesNumberOfStatesToAddressRegionalHaze / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActRelatedToRegionalHazeMember |  |
Public Utilities, Potential to emit tons per year of visibility impairing pollution, maximum |  |  | 250 pnm_PublicUtilitiesPotentialToEmitTonsPerYearOfVisibilityImpairingPollutionMaximum / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActRelatedToRegionalHazeMember |  |
San Juan Generating Station [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |
Jointly Owned Utility Plant, Proportionate Ownership Share |  |  |  | 46.30%us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |
San Juan Generating Station [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |
Public Utilities, Overall Reduction Of Ownership, in Megawatts |  | 340 pnm_PublicUtilitiesOverallReductionOfOwnershipinMegawatts / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |
San Juan Generating Station [Member] | Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Minimum [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SCR [Member] [Member] |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |
Estimated Total Capital Cost If Requirement Occurred |  |  |  | 824 pnm_EstimatedTotalCapitalCostIfRequirementOccurred / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSCRMemberMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_PublicUtilitiesCommitmentsAndContingenciesByNatureOfExpenseAxis = pnm_InstallationCostsIncludingConstructionManagementGrossReceiptsTaxesAfudcAndOtherPnmCostsMember / us-gaap_RangeAxis = us-gaap_MinimumMember |
San Juan Generating Station [Member] | Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Minimum [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |
Estimated Installation Capital Costs |  |  |  | 85.0 pnm_EstimatedInstallationCapitalCosts / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_PublicUtilitiesCommitmentsAndContingenciesByNatureOfExpenseAxis = pnm_InstallationCostsIncludingConstructionManagementGrossReceiptsTaxesAfudcAndOtherPnmCostsMember / us-gaap_RangeAxis = us-gaap_MinimumMember |
Estimated Portion of Total Capital Costs if Requirement Occured |  |  |  | 105 pnm_EstimatedPortionOfTotalCapitalCostsIfRequirementOccured / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_PublicUtilitiesCommitmentsAndContingenciesByNatureOfExpenseAxis = pnm_InstallationCostsIncludingConstructionManagementGrossReceiptsTaxesAfudcAndOtherPnmCostsMember / us-gaap_RangeAxis = us-gaap_MinimumMember |
San Juan Generating Station [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, SCR [Member] [Member] |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |
Estimated Total Capital Cost If Requirement Occurred |  |  |  | 910 pnm_EstimatedTotalCapitalCostIfRequirementOccurred / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSCRMemberMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_PublicUtilitiesCommitmentsAndContingenciesByNatureOfExpenseAxis = pnm_InstallationCostsIncludingConstructionManagementGrossReceiptsTaxesAfudcAndOtherPnmCostsMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
San Juan Generating Station [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 |  |  |  | 90.0 pnm_EstimatedInstallationCapitalCosts / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_PublicUtilitiesCommitmentsAndContingenciesByNatureOfExpenseAxis = pnm_InstallationCostsIncludingConstructionManagementGrossReceiptsTaxesAfudcAndOtherPnmCostsMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
Estimated Portion of Total Capital Costs if Requirement Occured |  |  |  | 110 pnm_EstimatedPortionOfTotalCapitalCostsIfRequirementOccured / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_PublicUtilitiesCommitmentsAndContingenciesByNatureOfExpenseAxis = pnm_InstallationCostsIncludingConstructionManagementGrossReceiptsTaxesAfudcAndOtherPnmCostsMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
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, Requested Time Period to Recover Retired Units NBV | 20 years | 20 years |  |  |
Public Utilities, Newly Identified Replacement Gas-fired Generation, in Megawatts, December2013 |  | 177 pnm_PublicUtilitiesNewlyIdentifiedReplacementGasfiredGenerationinMegawattsDecember2013 / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnits2And3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |
Public Utilities, Newly Identified Replacement Solar Generation, in Megawatts, December2013 |  | 40 pnm_PublicUtilitiesNewlyIdentifiedReplacementSolarGenerationinMegawattsDecember2013 / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnits2And3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |
San Juan Generating Station Units 2 and 3 [Member] | Pnm Electric [Member] |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |
Estimated cost of replacing gas fired peaking capacity due to retirement of SJGS units |  |  | 212.5 pnm_EstimatedCostOfReplacingGasFiredPeakingCapacityDueToRetirementOfSjgsUnits / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnits2And3Member / dei_LegalEntityAxis = pnm_PnmElectricMember |  |
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, 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 |  |  |
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 |  |  |
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
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, Ownership To Be Exchanged, in Megawatts |  | 78 pnm_PublicUtilitiesOwnershipToBeExchangedinMegawatts / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |

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