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Fair Value of Derivative and Other Financial Instruments - Sale of Power (Details) | Mar. 31, 2015 MW | Dec. 31, 2014
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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 | 134 pnm_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 |  | 37 us-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 |

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- Definition Percentage of Electric Power Plant Output Sold for 2014 and 2015 + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Public Utilities, Number of Megawatts Nuclear Generation + References No definition available. + Details
Name: | pnm_PublicUtilitiesNumberofMegawattsNuclearGeneration
Namespace Prefix: | pnm_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | instant

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- Definition The average forward price on the group of price risk forward or futures contracts, such as gas futures contracts. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | us-types:perUnitItemType
Balance Type: | na
Period Type: | instant

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- Details
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- Details
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Namespace Prefix: |
Data Type: | na
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- Details
Name: | us-gaap_JointlyOwnedUtilityPlantAxis=pnm_PaloVerdeNuclearGeneratingStationUnit3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |