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Commitments and Contingencies - Nuclear Spent Fuel and Waste Disposal (Details) (Palo Verde Nuclear Generating Station [Member], Public Service Company of New Mexico [Member], USD $) | 3 Months Ended |
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Mar. 31, 2015 | Dec. 31, 2014
Nuclear Spent Fuel And Waste Disposal [Member] |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |
Loss Contingency, Estimate of Possible Loss | $ 58,000,000 us-gaap_LossContingencyEstimateOfPossibleLoss / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = pnm_NuclearSpentFuelAndWasteDisposalMember |
Revised Annual Fee, Nuclear Waste Disposal | 0 pnm_RevisedAnnualFeeNuclearWasteDisposal / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = pnm_NuclearSpentFuelAndWasteDisposalMember |
Nuclear Spent Fuel And Waste Disposal [Member] | Other Deferred Credits [Member] |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |
Loss Contingency Accrual | 12,400,000 us-gaap_LossContingencyAccrualAtCarryingValue / pnm_FinancialStatementLocationAxis = pnm_OtherDeferredCreditsMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = pnm_NuclearSpentFuelAndWasteDisposalMember | 12,300,000 us-gaap_LossContingencyAccrualAtCarryingValue / pnm_FinancialStatementLocationAxis = pnm_OtherDeferredCreditsMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = pnm_NuclearSpentFuelAndWasteDisposalMember
Nuclear Spent Fuel And Waste Disposal [Member] | Settled Litigation [Member] |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |
Lawsuit settlement, third party receipt | 57,400,000 pnm_Lawsuitsettlementthirdpartyreceipt / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LitigationStatusAxis = us-gaap_SettledLitigationMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = pnm_NuclearSpentFuelAndWasteDisposalMember |
PNMs share of lawsuit settlement, third party receipt | 5,900,000 pnm_PNMsshareoflawsuitsettlementthirdpartyreceipt / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LitigationStatusAxis = us-gaap_SettledLitigationMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = pnm_NuclearSpentFuelAndWasteDisposalMember |
Department of energy, spent nuclear fuel removal July 2011 - June 2014 [Member] |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |
Lawsuit settlement, third party receipt | 42,000,000 pnm_Lawsuitsettlementthirdpartyreceipt / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = pnm_DepartmentofenergyspentnuclearfuelremovalJuly2011June2014Member |
PNMs share of third party settlement claim | 4,300,000 pnm_PNMsshareofthirdpartysettlementclaim / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = pnm_DepartmentofenergyspentnuclearfuelremovalJuly2011June2014Member |
Litigation Settlement, Portion credited to customers | $ 3,100,000 pnm_LitigationSettlementPortioncreditedtocustomers / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = pnm_DepartmentofenergyspentnuclearfuelremovalJuly2011June2014Member |

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