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Commitments and Contingencies - The Clean Air Act (Details) (USD $)
In Millions, unless otherwise specified
 0 Months Ended
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     50pnm_PublicUtilitiesNumberOfStatesToAddressRegionalHaze
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_CleanAirActRelatedToRegionalHazeMember		    
Public Utilities, Potential to emit tons per year of visibility impairing pollution, maximum     250pnm_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   340pnm_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       824pnm_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       85.0pnm_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       105pnm_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       910pnm_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       90.0pnm_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       110pnm_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   177pnm_PublicUtilitiesNewlyIdentifiedReplacementGasfiredGenerationinMegawattsDecember2013
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_CleanAirActSncrMember
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_SanJuanGeneratingStationUnits2And3Member
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember		      
Public Utilities, Newly Identified Replacement Solar Generation, in Megawatts, December2013   40pnm_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     212.5pnm_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 1,650pnm_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     134pnm_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 134pnm_PublicUtilitiesNumberofMegawattsNuclearGeneration
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_CleanAirActSncrMember
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_PaloVerdeNuclearGeneratingStationUnit3Member
/ dei_LegalEntityAxis
= pnm_PnmrAndPnmMember		 134pnm_PublicUtilitiesNumberofMegawattsNuclearGeneration
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_CleanAirActSncrMember
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_PaloVerdeNuclearGeneratingStationUnit3Member
/ dei_LegalEntityAxis
= pnm_PnmrAndPnmMember		      
Public Utilities, Proposed value per Kilowatt effective January 1, 2018   2,500pnm_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 90.6pnm_EstimatedInstallationCapitalCosts
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_CleanAirActSncrMember
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_SanJuanGeneratingStationUnits1And4Member
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ pnm_PublicUtilitiesCommitmentsAndContingenciesByNatureOfExpenseAxis
= pnm_InstallationCostsIncludingConstructionManagementGrossReceiptsTaxesAfudcAndOtherPnmCostsMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		 82.0pnm_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 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		 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
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   78pnm_PublicUtilitiesOwnershipToBeExchangedinMegawatts
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_CleanAirActSncrMember
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_SanJuanGeneratingStationUnit3Member
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember