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Commitments and Contingencies - SJGS Matters (Details) (USD $) | Jan. 07, 2015 MW | Jun. 26, 2014 | Mar. 31, 2015 | Oct. 01, 2014 MW | Dec. 20, 2013 MW | Jan. 22, 2015 | Jun. 27, 2014 | Mar. 11, 2014
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Clean Air Act, SNCR [Member] | San Juan Generating Station Unit 4 [Member] |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |
Public Utilities, Unsubscribed Ownership in Megawatts | 65 pnm_PublicUtilitiesUnsubscribedOwnershipinMegawatts / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station Unit 4 [Member] |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |
Jointly Owned Utility Plan, Proposed Proportionate Ownership Share |  | 64.50%pnm_JointlyOwnedUtilityPlanProposedProportionateOwnershipShare / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station Units 1 and 4 [Member] |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |
Jointly Owned Utility Plan, Proposed Proportionate Ownership Share |  | 58.70%pnm_JointlyOwnedUtilityPlanProposedProportionateOwnershipShare / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnits1And4Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member] | San Juan Generating Station Unit 3 [Member] |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |
Percentage of ownership held by exiting owners |  |  | 50.00%pnm_Percentageofownershipheldbyexitingowners / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |
Public Utilities, Ownership Percentage |  |  | 50.00%pnm_PublicUtilitiesOwnershipPercentage / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |
Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member] | San Juan Generating Station Unit 4 [Member] |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |
Percentage of ownership held by exiting owners |  |  | 38.80%pnm_Percentageofownershipheldbyexitingowners / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |
Public Utilities, Ownership Percentage |  |  | 38.50%pnm_PublicUtilitiesOwnershipPercentage / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |
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 | 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 | 78 pnm_PublicUtilitiesAdditionalOwnershipToBeObtainedinMegawatts / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |
Public Utilities, Costs to obtain additional ownership |  | 0 pnm_PublicUtilitiesCoststoobtainadditionalownership / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member] | Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | San Juan Generating Station Unit 4 [Member] |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |
Requested Expenditure, Installation Capital Costs |  |  |  |  |  | 76,600,000 pnm_RequestedExpenditureInstallationCapitalCosts / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_PublicUtilitiesCommitmentsAndContingenciesByNatureOfExpenseAxis = pnm_InstallationCostsIncludingConstructionManagementGrossReceiptsTaxesAfudcAndOtherPnmCostsMember |  | 1,900,000 pnm_RequestedExpenditureInstallationCapitalCosts / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_PublicUtilitiesCommitmentsAndContingenciesByNatureOfExpenseAxis = pnm_InstallationCostsIncludingConstructionManagementGrossReceiptsTaxesAfudcAndOtherPnmCostsMember
Requested Additional Expenditure, Installation Capital Costs |  |  |  |  |  |  | $ 6,400,000 pnm_RequestedAdditionalExpenditureInstallationCapitalCosts / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_PublicUtilitiesCommitmentsAndContingenciesByNatureOfExpenseAxis = pnm_InstallationCostsIncludingConstructionManagementGrossReceiptsTaxesAfudcAndOtherPnmCostsMember |
PNMR Development [Member] | Clean Air Act, SNCR [Member] | San Juan Generating Station Unit 4 [Member] |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |
Public Utilities, Potential Acquisition of Ownership in Megawatts | 65 pnm_PublicUtilitiesPotentialAcquisitionofOwnershipinMegawatts / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member / dei_LegalEntityAxis = pnm_PNMRDevelopmentMember |  | 65 pnm_PublicUtilitiesPotentialAcquisitionofOwnershipinMegawatts / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member / dei_LegalEntityAxis = pnm_PNMRDevelopmentMember |  |  |  |  |

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