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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
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 65pnm_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   132pnm_PublicUtilitiesAdditionalOwnershipToBeObtainedinMegawatts
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_CleanAirActSncrMember
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_SanJuanGeneratingStationUnit4Member
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember		 132pnm_PublicUtilitiesAdditionalOwnershipToBeObtainedinMegawatts
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_CleanAirActSncrMember
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_SanJuanGeneratingStationUnit4Member
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember		 132pnm_PublicUtilitiesAdditionalOwnershipToBeObtainedinMegawatts
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_CleanAirActSncrMember
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_SanJuanGeneratingStationUnit4Member
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember		 78pnm_PublicUtilitiesAdditionalOwnershipToBeObtainedinMegawatts
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_CleanAirActSncrMember
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_SanJuanGeneratingStationUnit4Member
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember		      
Public Utilities, Costs to obtain additional ownership   0pnm_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           76,600,000pnm_RequestedExpenditureInstallationCapitalCosts
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_CleanAirActSncrMember
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_SanJuanGeneratingStationUnit4Member
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ pnm_PublicUtilitiesCommitmentsAndContingenciesByNatureOfExpenseAxis
= pnm_InstallationCostsIncludingConstructionManagementGrossReceiptsTaxesAfudcAndOtherPnmCostsMember		   1,900,000pnm_RequestedExpenditureInstallationCapitalCosts
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_CleanAirActSncrMember
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_SanJuanGeneratingStationUnit4Member
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ pnm_PublicUtilitiesCommitmentsAndContingenciesByNatureOfExpenseAxis
= pnm_InstallationCostsIncludingConstructionManagementGrossReceiptsTaxesAfudcAndOtherPnmCostsMember
Requested Additional Expenditure, Installation Capital Costs             $ 6,400,000pnm_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 65pnm_PublicUtilitiesPotentialAcquisitionofOwnershipinMegawatts
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_CleanAirActSncrMember
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_SanJuanGeneratingStationUnit4Member
/ dei_LegalEntityAxis
= pnm_PNMRDevelopmentMember		   65pnm_PublicUtilitiesPotentialAcquisitionofOwnershipinMegawatts
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_CleanAirActSncrMember
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_SanJuanGeneratingStationUnit4Member
/ dei_LegalEntityAxis
= pnm_PNMRDevelopmentMember