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Fair Value of Derivative and Other Financial Instruments - Sale of Power (Details)
Mar. 31, 2015
MW
Dec. 31, 2014
Palo Verde Nuclear Generating Station Unit 3 [Member] | PNMR and PNM [Member]    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [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] | Commodity Contract [Member]    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Derivative, Average Forward Price   37us-gaap_DerivativeAverageForwardPrice
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_PaloVerdeNuclearGeneratingStationUnit3Member
/ dei_LegalEntityAxis
= pnm_PnmrAndPnmMember
Firm Contract [Member] | Palo Verde Nuclear Generating Station [Member] | Public Service Company of New Mexico [Member]    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Percentage of Electric Power Plant Output Sold for 2014 and 2015 100.00%pnm_PercentageofElectricPowerPlantOutputSoldfor2014and2015
/ pnm_ClassificationOfContractAxis
= pnm_FirmContractMember
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_PaloVerdeNuclearGeneratingStationMember
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember