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Commitments and Contingencies (Details) (USD $) | 12 Months Ended | 0 Months Ended |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Oct. 01, 2014 | Dec. 20, 2013 MW | Dec. 21, 2011 mw | Jun. 26, 2014 | Oct. 31, 2014 | Oct. 31, 2012 | Sep. 30, 2014 | Nov. 25, 2014 opp | Jan. 31, 2010 opp | Apr. 12, 2012 | Jun. 27, 2014 | Mar. 11, 2014 | May 23, 2013 | Jan. 06, 2014 Allotment_Parcel | Sep. 01, 2012 Allotment_Parcel | Nov. 08, 2013 | Jan. 07, 2015 MW | Jan. 15, 2015 MW | Jan. 22, 2015
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum Megawatt Capacity from Coal and Oil-Fired Electric Generating Units under Jurisdiction of the Merucy and Air Toxics Standards |  |  |  |  |  |  | 25pnm_MinimumMegawattCapacityFromCoalAndOilFiredElectricGeneratingUnitsUnderJurisdictionOfMerucyAndAirToxicsStandards |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other current assets | $ 58,471,000us-gaap_OtherAssetsCurrent |  | $ 34,590,000us-gaap_OtherAssetsCurrent |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Mercury Removal Rate, Percentage |  |  |  |  |  |  | 99.00%pnm_MercuryRemovalRatePercentage / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Four Corners [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Jointly Owned Utility Plant, Sale of Ownership Percentage |  |  | 48.00%pnm_PublicUtilitiesJointlyOwnedUtilityPlantSaleofOwnershipPercentage / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_FourCornersMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets | 401,025,000us-gaap_RegulatoryAssets / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  | 403,611,000us-gaap_RegulatoryAssets / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station Unit 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss 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] | Palo Verde Nuclear Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to Acquire Investments to be Held in Decommissioning Trust Fund | 4,900,000us-gaap_PaymentsToInvestInDecommissioningFund / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  | 4,900,000us-gaap_PaymentsToInvestInDecommissioningFund / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 2,600,000us-gaap_PaymentsToInvestInDecommissioningFund / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Decommissioning Fund Investments, Fair Value | 244,600,000us-gaap_DecommissioningTrustAssetsAmount / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  | 222,500,000us-gaap_DecommissioningTrustAssetsAmount / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Jointly Owned Utility Plant, Proportionate Ownership Share | 10.20%us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station [Member] | Nuclear Spent Fuel And Waste Disposal [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingency, Estimate of Possible Loss | 58,000,000us-gaap_LossContingencyEstimateOfPossibleLoss / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = pnm_NuclearSpentFuelAndWasteDisposalMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual Fee, Nuclear Waste Disposal | 0pnm_AnnualFeeNuclearWasteDisposal / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = pnm_NuclearSpentFuelAndWasteDisposalMember |  | 3,000,000pnm_AnnualFeeNuclearWasteDisposal / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = pnm_NuclearSpentFuelAndWasteDisposalMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station [Member] | Department of energy, spent nuclear fuel removal July 2011 - June 2014 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Lawsuit settlement, Third party settlement claim |  |  |  |  |  |  |  |  | 42,500,000pnm_LawsuitsettlementThirdpartysettlementclaim / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = pnm_DepartmentofenergyspentnuclearfuelremovalJuly2011June2014Member |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNMs share of third party settlement claim |  |  |  |  |  |  |  |  | 4,300,000pnm_PNMsshareofthirdpartysettlementclaim / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = pnm_DepartmentofenergyspentnuclearfuelremovalJuly2011June2014Member |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Jointly Owned Utility Plant, Proportionate Ownership Share |  |  |  |  |  |  |  |  |  | 46.30%us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station Units 2 and 3 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net book value | 282,000,000pnm_NetBookValue / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnits2And3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Four Corners Units 4 and 5 (Coal) [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Jointly Owned Utility Plant, Proportionate Ownership Share | 13.00%us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_FourCornersUnits4And5CoalMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station Unit 3 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net book value |  |  |  |  |  |  |  |  |  |  | 144,000,000pnm_NetBookValue / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station Units 1 and 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss 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] | Other Deferred Credits [Member] | Palo Verde Nuclear Generating Station [Member] | Nuclear Spent Fuel And Waste Disposal [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Mine Reclamation and Closing Liability, Noncurrent | 12,300,000us-gaap_LossContingencyAccrualAtCarryingValue / pnm_FinancialStatementLocationAxis = pnm_OtherDeferredCreditsMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = pnm_NuclearSpentFuelAndWasteDisposalMember |  | 11,900,000us-gaap_LossContingencyAccrualAtCarryingValue / pnm_FinancialStatementLocationAxis = pnm_OtherDeferredCreditsMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = pnm_NuclearSpentFuelAndWasteDisposalMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Minimum [Member] | San Juan Generating Station And Four Corners [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Proposed Government Standard Emission Limit |  |  |  |  |  |  |  |  |  |  |  | 65pnm_PublicUtilitiesProposedGovernmentStandardEmissionLimit / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationAndFourCornersMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RangeAxis = us-gaap_MinimumMember | 60pnm_PublicUtilitiesProposedGovernmentStandardEmissionLimit / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationAndFourCornersMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RangeAxis = us-gaap_MinimumMember |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Maximum [Member] | San Juan Generating Station And Four Corners [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Government Standard Emission Limit (pounds per MMBTU, parts per million) | 75pnm_PublicUtilitiesGovernmentStandardEmissionLimit / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationAndFourCornersMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Proposed Government Standard Emission Limit |  |  |  |  |  |  |  |  |  |  |  | 70pnm_PublicUtilitiesProposedGovernmentStandardEmissionLimit / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationAndFourCornersMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RangeAxis = us-gaap_MaximumMember | 70pnm_PublicUtilitiesProposedGovernmentStandardEmissionLimit / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationAndFourCornersMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Coal Supply [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other current assets | 37,300,000us-gaap_OtherAssetsCurrent / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PurchaseCommitmentExcludingLongtermCommitmentAxis = pnm_CoalSupplyMember |  | 12,300,000us-gaap_OtherAssetsCurrent / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PurchaseCommitmentExcludingLongtermCommitmentAxis = pnm_CoalSupplyMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Estimated Increase in Coal Cost, Percentage | 30.00%pnm_PublicUtilitiesEstimatedIncreaseinCoalCostPercentage / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PurchaseCommitmentExcludingLongtermCommitmentAxis = pnm_CoalSupplyMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Surface [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets | 100,000,000us-gaap_RegulatoryAssets / pnm_ClassificationOfMineAxis = pnm_SurfaceMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Surface [Member] | Loss on Long-term Purchase Commitment [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Mine Reclamation and Closing Liability, Noncurrent | 25,700,000us-gaap_LossContingencyAccrualAtCarryingValue / pnm_ClassificationOfMineAxis = pnm_SurfaceMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = us-gaap_LossOnLongTermPurchaseCommitmentMember |  | 23,800,000us-gaap_LossContingencyAccrualAtCarryingValue / pnm_ClassificationOfMineAxis = pnm_SurfaceMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = us-gaap_LossOnLongTermPurchaseCommitmentMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Final Reclamation, capped amount to be collected | 100,000,000pnm_FinalReclamationCappedAmountToBeCollected / pnm_ClassificationOfMineAxis = pnm_SurfaceMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = us-gaap_LossOnLongTermPurchaseCommitmentMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Surface [Member] | San Juan Generating Station [Member] | Loss on Long-term Purchase Commitment [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingency, Estimate of Possible Loss | 57,300,000us-gaap_LossContingencyEstimateOfPossibleLoss / pnm_ClassificationOfMineAxis = pnm_SurfaceMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = us-gaap_LossOnLongTermPurchaseCommitmentMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Underground [Member] | Loss on Long-term Purchase Commitment [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Mine Reclamation and Closing Liability, Noncurrent | 8,600,000us-gaap_LossContingencyAccrualAtCarryingValue / pnm_ClassificationOfMineAxis = pnm_UndergroundMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = us-gaap_LossOnLongTermPurchaseCommitmentMember |  | 7,800,000us-gaap_LossContingencyAccrualAtCarryingValue / pnm_ClassificationOfMineAxis = pnm_UndergroundMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = us-gaap_LossOnLongTermPurchaseCommitmentMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Underground [Member] | San Juan Generating Station [Member] | Loss on Long-term Purchase Commitment [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingency, Estimate of Possible Loss | 93,300,000us-gaap_LossContingencyEstimateOfPossibleLoss / pnm_ClassificationOfMineAxis = pnm_UndergroundMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = us-gaap_LossOnLongTermPurchaseCommitmentMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Nuclear Plant [Member] | Palo Verde Nuclear Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Ownership Percentage in Nuclear Reactor | 10.20%pnm_PublicUtilitiesOwnershipPercentageInNuclearReactor / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PublicUtilityAxis = us-gaap_NuclearPlantMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Maximum Potential Assessment Per Incident | 38,900,000pnm_PublicUtilitiesMaximumPotentialAssessmentPerIncident / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PublicUtilityAxis = us-gaap_NuclearPlantMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Annual Payment Limitation Related to Incident | 5,700,000pnm_PublicUtilitiesAnnualPaymentLimitationRelatedToIncident / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PublicUtilityAxis = us-gaap_NuclearPlantMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Aggregate Amount of All Risk Insurance | 2,750,000,000pnm_PublicUtilitiesAggregateAmountOfAllRiskInsurance / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PublicUtilityAxis = us-gaap_NuclearPlantMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Sublimit Amount under Nuclear Electric Insurance Limited | 2,250,000,000pnm_PublicUtilitiesSublimitAmountUnderNuclearElectricInsuranceLimited / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PublicUtilityAxis = us-gaap_NuclearPlantMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Maximum Amount under Nuclear Electic Insurance Limited | 4,800,000pnm_PublicUtilitiesMaximumAmountUnderNuclearElecticInsuranceLimited / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PublicUtilityAxis = us-gaap_NuclearPlantMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Nuclear Plant [Member] | Maximum [Member] | Palo Verde Nuclear Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Liability Insurance Coverage | 13,600,000,000pnm_PublicUtilitiesLiabilityInsuranceCoverage / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PublicUtilityAxis = us-gaap_NuclearPlantMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Commercial Providers [Member] | Nuclear Plant [Member] | Palo Verde Nuclear Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Liability Insurance Coverage | 375,000,000pnm_PublicUtilitiesLiabilityInsuranceCoverage / pnm_InsuranceCarrierAxis = pnm_CommercialProvidersMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PublicUtilityAxis = us-gaap_NuclearPlantMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Industry Wide Retrospective Assessment Program [Member] | Nuclear Plant [Member] | Palo Verde Nuclear Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Liability Insurance Coverage | 13,200,000,000pnm_PublicUtilitiesLiabilityInsuranceCoverage / pnm_InsuranceCarrierAxis = pnm_IndustryWideRetrospectiveAssessmentProgramMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PublicUtilityAxis = us-gaap_NuclearPlantMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pnm Electric [Member] | San Juan Generating Station Units 2 and 3 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated cost of replacing gas fired peaking capacity due to retirement of SJGS units | 268,400,000pnm_EstimatedCostOfReplacingGasFiredPeakingCapacityDueToRetirementOfSjgsUnits / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnits2And3Member / dei_LegalEntityAxis = pnm_PnmElectricMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNMR and PNM [Member] | Palo Verde Nuclear Generating Station Unit 3 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Number of Megawatts Nuclear Generation | 134pnm_PublicUtilitiesNumberofMegawattsNuclearGeneration / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PnmrAndPnmMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fuel and purchased power adjustment clause [Member] | Public Service Company of New Mexico [Member] | Minimum [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preliminary estimate increased deferral related to mine fire incident | 17,400,000pnm_PreliminaryEstimateIncreasedDeferralRelatedToMineFireIncident / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_RegulatoryAssetAxis = pnm_FuelAndPurchasedPowerAdjustmentClauseMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fuel and purchased power adjustment clause [Member] | Public Service Company of New Mexico [Member] | Maximum [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preliminary estimate increased deferral related to mine fire incident | 21,600,000pnm_PreliminaryEstimateIncreasedDeferralRelatedToMineFireIncident / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_RegulatoryAssetAxis = pnm_FuelAndPurchasedPowerAdjustmentClauseMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Clean Air Act related to Regional Haze [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss 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 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | San Juan Generating Station Unit 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Estimated rate base value at 1/1/2018 |  |  |  |  | 26,000,000pnm_PublicUtilitiesEstimatedratebasevalueat112018 / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station Unit 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss 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 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
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, Costs to obtain additional ownership |  |  |  |  |  |  |  | 0pnm_PublicUtilitiesCoststoobtainadditionalownership / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss 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 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station Units 2 and 3 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Time Period to Recover Retired Units NBV |  |  |  |  | 20 years | 20 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Number of Mega Watts of Gas-fired Generation |  |  |  |  |  | 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 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Recovery Percentage of Estimated undepreciated value at 12/31/17 |  |  |  |  | 50.00%pnm_PublicUtilitiesRecoveryPercentageofEstimatedundepreciatedvalueat123117 / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnits2And3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Estimated undepreciated value at 12/31/17 |  |  |  |  | 231,000,000pnm_PublicUtilitiesEstimatedundepreciatedvalueat123117 / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnits2And3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Write-off Percentage of Estimated undepreciated value at 12/31/17 |  |  |  |  | 50.00%pnm_PublicUtilitiesWriteoffPercentageofEstimatedundepreciatedvalueat123117 / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnits2And3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station Unit 3 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss 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 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Estimated rate base value at 1/1/2018 |  |  |  |  | 221,100,000pnm_PublicUtilitiesEstimatedratebasevalueat112018 / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station Unit 3 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss 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 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Proposed reduction in carrying value |  |  |  |  | 26,000,000pnm_PublicUtilitiesProposedreductionincarryingvalue / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities,Estimated unrecoverable increase in operations and maintenance |  |  |  |  | 20,000,000pnm_PublicUtilitiesEstimatedunrecoverableincreaseinoperationsandmaintenance / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | Minimum [Member] | San Juan Generating Station Unit 3 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities,Estimated pre-tax regulatory disallowance |  |  |  |  | 60,000,000pnm_PublicUtilitiesEstimatedpretaxregulatorydisallowance / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RangeAxis = us-gaap_MinimumMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | Maximum [Member] | San Juan Generating Station Unit 3 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities,Estimated pre-tax regulatory disallowance |  |  |  |  | 70,000,000pnm_PublicUtilitiesEstimatedpretaxregulatorydisallowance / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | PNMR and PNM [Member] | Palo Verde Nuclear Generating Station Unit 3 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss 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 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Percentage capacity factor 7-year performance threshold |  |  |  |  | 75.00%pnm_PublicUtilitiesPercentagecapacityfactor7yearperformancethreshold / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationUnit3Member / dei_LegalEntityAxis = pnm_PnmrAndPnmMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Period over which to measure capacity performance |  |  |  |  | 7 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Clean Air Act related to Post-Combustion Controls [Member] | Public Service Company of New Mexico [Member] | Four Corners [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingency, Estimate of Possible Loss | 80,000,000us-gaap_LossContingencyEstimateOfPossibleLoss / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActRelatedToPostCombustionControlsMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_FourCornersMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Number of Compliance alternatives | 2pnm_PublicUtilitiesNumberOfComplianceAlternatives / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActRelatedToPostCombustionControlsMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_FourCornersMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Government Standard Emission Limit (pounds per MMBTU, parts per million) | 0.015pnm_PublicUtilitiesGovernmentStandardEmissionLimit / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActRelatedToPostCombustionControlsMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_FourCornersMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilitites, Plant Requirment to Meet Opacity Limit, Percentage | 20.00%pnm_PublicUtilititesPlantRequirmentToMeetOpacityLimitPercentage / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActRelatedToPostCombustionControlsMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_FourCornersMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Rule Imposes Opacity Limitation on Certain Fugitive Dust Emissions From Coal and Material Handling Operations | 20.00%pnm_PublicUtilitiesRuleImposesOpacityLimitationOnCertainFugitiveDustEmissionsFromCoalAndMaterialHandlingOperations / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActRelatedToPostCombustionControlsMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_FourCornersMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Clean Air Act related to Post-Combustion Controls [Member] | Public Service Company of New Mexico [Member] | Four Corners Units 4 and 5 (Coal) [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Ownership Percentage | 13.00%pnm_PublicUtilitiesOwnershipPercentage / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActRelatedToPostCombustionControlsMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_FourCornersUnits4And5CoalMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Mercury Control [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Current Annual Mercury Control Costs | 700,000pnm_CurrentAnnualMercuryControlCosts / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_MercuryControlMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Mercury Control [Member] | Public Service Company of New Mexico [Member] | Maximum [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contingent Estimated Annual Mercury Control Cost | 6,600,000pnm_ContingentEstimatedAnnualMercuryControlCost / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_MercuryControlMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sierra Club Allegations [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated Total Litigation Settlement Cost |  |  |  |  |  |  |  |  |  |  |  |  |  | 10,200,000pnm_EstimatedTotalLitigationSettlementCost / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_SierraClubAllegationsMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember |  |  |  |  |  |  |  |  |
Sierra Club Allegations [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated Company Share Litigation Settlement Cost |  |  |  |  |  |  |  |  |  |  |  |  |  | 4,500,000pnm_EstimatedCompanyShareLitigationSettlementCost / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_SierraClubAllegationsMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |
Loss on Long-term Purchase Commitment [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Annual Funding | 1,000,000pnm_PublicUtilitiesAnnualFunding / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = us-gaap_LossOnLongTermPurchaseCommitmentMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  | 300,000pnm_PublicUtilitiesAnnualFunding / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = us-gaap_LossOnLongTermPurchaseCommitmentMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 3,500,000pnm_PublicUtilitiesAnnualFunding / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = us-gaap_LossOnLongTermPurchaseCommitmentMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Expected Funding Annual Requirements | 600,000pnm_PublicUtilitiesExpectedFundingAnnualRequirements / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = us-gaap_LossOnLongTermPurchaseCommitmentMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Clean Air Act, SCR [Member] | Public Service Company of New Mexico [Member] | Minimum [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated Total Capital Cost If Requirement Occurred |  |  |  |  |  |  |  |  |  | 824,000,000pnm_EstimatedTotalCapitalCostIfRequirementOccurred / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSCRMemberMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_PublicUtilitiesCommitmentsAndContingenciesByNatureOfExpenseAxis = pnm_InstallationCostsIncludingConstructionManagementGrossReceiptsTaxesAfudcAndOtherPnmCostsMember / us-gaap_RangeAxis = us-gaap_MinimumMember |  |  |  |  |  |  |  |  |  |  |  |  |
Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Clean Air Act, SCR [Member] | Public Service Company of New Mexico [Member] | Maximum [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated Total Capital Cost If Requirement Occurred |  |  |  |  |  |  |  |  |  | 910,000,000pnm_EstimatedTotalCapitalCostIfRequirementOccurred / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSCRMemberMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_PublicUtilitiesCommitmentsAndContingenciesByNatureOfExpenseAxis = pnm_InstallationCostsIncludingConstructionManagementGrossReceiptsTaxesAfudcAndOtherPnmCostsMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |  |  |  |  |  |  |  |  |  |  |
Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station Unit 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested Expenditure, Installation Capital Costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 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 |  |  |  |  |  |  |  |
Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | Minimum [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated Installation Capital Costs |  |  |  |  |  |  |  |  |  | 85,000,000pnm_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 |  |  |  |  |  |  |  |  |  | 105,000,000pnm_EstimatedPortionOfTotalCapitalCostsIfRequirementOccured / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_PublicUtilitiesCommitmentsAndContingenciesByNatureOfExpenseAxis = pnm_InstallationCostsIncludingConstructionManagementGrossReceiptsTaxesAfudcAndOtherPnmCostsMember / us-gaap_RangeAxis = us-gaap_MinimumMember |  |  |  |  |  |  |  |  |  |  |  |  |
Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | Maximum [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated Installation Capital Costs |  |  |  |  |  |  |  |  |  | 90,000,000pnm_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 |  |  |  |  |  |  |  |  |  | 110,000,000pnm_EstimatedPortionOfTotalCapitalCostsIfRequirementOccured / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_PublicUtilitiesCommitmentsAndContingenciesByNatureOfExpenseAxis = pnm_InstallationCostsIncludingConstructionManagementGrossReceiptsTaxesAfudcAndOtherPnmCostsMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |  |  |  |  |  |  |  |  |  |  |
Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | Maximum [Member] | San Juan Generating Station Units 1 and 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated Installation Capital Costs |  |  |  |  | 90,600,000pnm_EstimatedInstallationCapitalCosts / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnits1And4Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_PublicUtilitiesCommitmentsAndContingenciesByNatureOfExpenseAxis = pnm_InstallationCostsIncludingConstructionManagementGrossReceiptsTaxesAfudcAndOtherPnmCostsMember / us-gaap_RangeAxis = us-gaap_MaximumMember | 82,000,000pnm_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 Underground Mine Fire [Member] | Fuel and purchased power adjustment clause [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Insurance Recovery | 18,700,000pnm_PublicUtilitiesInsuranceRecovery / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_OtherCommitmentsAxis = pnm_SanJuanUndergroundMineFireMember / us-gaap_RegulatoryAssetAxis = pnm_FuelAndPurchasedPowerAdjustmentClauseMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NMTRD Coal Severance Tax [Member] | Four Corners [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Assessed Coal Severance Surtax Penalty and Interest |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 30,000,000pnm_PublicUtilitiesAssessedCoalSeveranceSurtaxPenaltyandInterest / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_FourCornersMember / us-gaap_OtherCommitmentsAxis = pnm_NMTRDCoalSeveranceTaxMember |  |  |  |  |  |
NMTRD Coal Severance Tax [Member] | Public Service Company of New Mexico [Member] | Four Corners [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, PNM Share Assessed Coal Severance Surtax Penalty and Interest to pass through FFPAC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9.40%pnm_PublicUtilitiesPNMShareAssessedCoalSeveranceSurtaxPenaltyandInteresttopassthroughFFPAC / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_FourCornersMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_OtherCommitmentsAxis = pnm_NMTRDCoalSeveranceTaxMember |  |  |  |  |  |
Navajo Nation Allottee Matters [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of landowners claiming to be Navajo allottees |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 43pnm_NumberoflandownersclaimingtobeNavajoallottees / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_OtherCommitmentsAxis = pnm_NavajoNationAllotteeMattersMember |  |  |  |
Number of allotment parcels' appraisal requested for review |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 58pnm_Numberofallotmentparcelsappraisalrequestedforreview / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_OtherCommitmentsAxis = pnm_NavajoNationAllotteeMattersMember |  |  |  |  |
San Juan Generating Station [Member] | National Ambient Air Quality Standards [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Revised SO2 Emissions Agreed Upon |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.10pnm_PublicUtilitiesRevisedSO2EmissionsAgreedUpon / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_NationalAmbientAirQualityStandardsMember / pnm_JointlyOwnedGeneratingFacilitiesAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |
San Juan Generating Station [Member] | Continuous Highwall Mining [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Proposed Retroactive Surface Mining Royalty Rate | 12.50%pnm_PublicUtilitiesProposedRetroactiveSurfaceMiningRoyaltyRate / pnm_JointlyOwnedGeneratingFacilitiesAxis = pnm_SanJuanGeneratingStationMember / us-gaap_OtherCommitmentsAxis = pnm_ContinuousHighwallMiningMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Current Surface Mining Royalty Rate applied between 2000 and 2003 | 8.00%pnm_PublicUtilitiesCurrentSurfaceMiningRoyaltyRateappliedbetween2000and2003 / pnm_JointlyOwnedGeneratingFacilitiesAxis = pnm_SanJuanGeneratingStationMember / us-gaap_OtherCommitmentsAxis = pnm_ContinuousHighwallMiningMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Estimated Underpaid Surface Mining Royalties under proposed rate change | 5,000,000pnm_PublicUtilitiesEstimatedUnderpaidSurfaceMiningRoyaltiesunderproposedratechange / pnm_JointlyOwnedGeneratingFacilitiesAxis = pnm_SanJuanGeneratingStationMember / us-gaap_OtherCommitmentsAxis = pnm_ContinuousHighwallMiningMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, PNM Share Estimated Underpaid Surface Mining Royalties under proposed rate change | 46.30%pnm_PublicUtilitiesPNMShareEstimatedUnderpaidSurfaceMiningRoyaltiesunderproposedratechange / pnm_JointlyOwnedGeneratingFacilitiesAxis = pnm_SanJuanGeneratingStationMember / us-gaap_OtherCommitmentsAxis = pnm_ContinuousHighwallMiningMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
San Juan Generating Station [Member] | SJCC Arbitration [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Potential Unbilled Mining Costs Owed to SJCC | 5,200,000.0pnm_PublicUtilitiesPotentialUnbilledMiningCostsOwedtoSJCC / pnm_JointlyOwnedGeneratingFacilitiesAxis = pnm_SanJuanGeneratingStationMember / us-gaap_OtherCommitmentsAxis = pnm_SJCCArbitrationMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Potential Overbilled Mining Costs SJCC Owes to SJGS Owners | 1,100,000.0pnm_PublicUtilitiesPotentialOverbilledMiningCostsSJCCOwestoSJGSOwners / pnm_JointlyOwnedGeneratingFacilitiesAxis = pnm_SanJuanGeneratingStationMember / us-gaap_OtherCommitmentsAxis = pnm_SJCCArbitrationMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Potential Capital Improvements billed as Mining Costs to SJGS Owners | 13,900,000.0pnm_PublicUtilitiesPotentialCapitalImprovementsbilledasMiningCoststoSJGSOwners / pnm_JointlyOwnedGeneratingFacilitiesAxis = pnm_SanJuanGeneratingStationMember / us-gaap_OtherCommitmentsAxis = pnm_SJCCArbitrationMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
San Juan Generating Station [Member] | SJCC Arbitration [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, PNM Share of arbitration ruling | 46.30%pnm_PublicUtilitiesPNMShareofarbitrationruling / pnm_JointlyOwnedGeneratingFacilitiesAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_OtherCommitmentsAxis = pnm_SJCCArbitrationMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, FFPAC Percentage of mining costs overbilled or unbilled ruled by arbitration | 33.00%pnm_PublicUtilitiesFFPACPercentageofminingcostsoverbilledorunbilledruledbyarbitration / pnm_JointlyOwnedGeneratingFacilitiesAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_OtherCommitmentsAxis = pnm_SJCCArbitrationMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settled Litigation [Member] | Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station [Member] | Department of energy, spent nuclear fuel removal January 2007 - June 2011 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Lawsuit settlement, third party receipt | 57,400,000pnm_Lawsuitsettlementthirdpartyreceipt / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LitigationStatusAxis = us-gaap_SettledLitigationMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = pnm_DepartmentofenergyspentnuclearfuelremovalJanuary2007June2011Member |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settled Litigation [Member] | Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station [Member] | Nuclear Spent Fuel And Waste Disposal [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNMs share of lawsuit settlement, third party receipt | 5,900,000pnm_PNMsshareoflawsuitsettlementthirdpartyreceipt / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LitigationStatusAxis = us-gaap_SettledLitigationMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = pnm_NuclearSpentFuelAndWasteDisposalMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Member] | Clean Air Act, SNCR [Member] | San Juan Generating Station Unit 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Unsubscribed Ownership in Megawatts |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 65pnm_PublicUtilitiesUnsubscribedOwnershipinMegawatts / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |
Subsequent Event [Member] | Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station Unit 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Ownership in Megawatts PNM has agreed not to obtain |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 65pnm_PublicUtilitiesOwnershipinMegawattsPNMhasagreednottoobtain / pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis = pnm_CleanAirActSncrMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SanJuanGeneratingStationUnit4Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |
Subsequent Event [Member] | Clean Air Act, SNCR [Member] | PNMR [Member] | San Juan Generating Station Unit 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss 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_PnmrMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |
Subsequent Event [Member] | Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station Unit 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss 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 / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
[1] | Includes interest in PVNGS Unit 3, interest in common facilities for all PVNGS units, and owned interests in PVNGS Units 1 and 2.

X
- Definition Annual Fee, Nuclear Waste Disposal + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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- Definition Contingent Estimated Annual Mercury Control Cost + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Current Annual Mercury Control Costs + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Estimated Company Share Litigation Settlement Cost + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition estimated cost of replacing gas fired peaking capacity due to retirement of SJGS units + References No definition available. + Details
Name: | pnm_EstimatedCostOfReplacingGasFiredPeakingCapacityDueToRetirementOfSjgsUnits
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Estimated Installation Capital Costs + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Estimated Portion of Total Capital Costs if Requirement Occured + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Estimated Total Capital Cost If Requirement Occurred + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Estimated Total Litigation Settlement Cost + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Final Reclamation, capped amount to be collected + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Jointly Owned Utility Plan, Proposed Proportionate Ownership Share + References No definition available. + Details
Name: | pnm_JointlyOwnedUtilityPlanProposedProportionateOwnershipShare
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Lawsuit settlement, third party receipt + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Lawsuit settlement, Third party settlement claim + References No definition available. + Details
Name: | pnm_LawsuitsettlementThirdpartysettlementclaim
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Mercury Removal Rate, Percentage + References No definition available. + Details
Name: | pnm_MercuryRemovalRatePercentage
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Minimum Megawatt Capacity from Coal and Oil-Fired Electric Generating Units under Jurisdiction of the Merucy and Air Toxics Standards + References No definition available. + Details
Name: | pnm_MinimumMegawattCapacityFromCoalAndOilFiredElectricGeneratingUnitsUnderJurisdictionOfMerucyAndAirToxicsStandards
Namespace Prefix: | pnm_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

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- Definition Net book value + References No definition available. + Details
Name: | pnm_NetBookValue
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Number of allotment parcels' appraisal requested for review + References No definition available. + Details
Name: | pnm_Numberofallotmentparcelsappraisalrequestedforreview
Namespace Prefix: | pnm_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Definition Number of landowners claiming to be Navajo allottees + References No definition available. + Details
Name: | pnm_NumberoflandownersclaimingtobeNavajoallottees
Namespace Prefix: | pnm_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Definition Percentage of ownership held by exiting owners + References No definition available. + Details
Name: | pnm_Percentageofownershipheldbyexitingowners
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition PNMs share of lawsuit settlement, third party receipt + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition PNMs share of third party settlement claim + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Preliminary estimate increased deferral related to mine fire incident + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Public Utilities, Additional Ownership To Be Obtained, in Megawatts + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Aggregate Amount of All Risk Insurance + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Public Utilities, Annual Funding + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Public Utilities, Annual Payment Limitation Related to Incident + References No definition available. + Details
Name: | pnm_PublicUtilitiesAnnualPaymentLimitationRelatedToIncident
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Public Utilities, Assessed Coal Severance Surtax Penalty and Interest + References No definition available. + Details
Name: | pnm_PublicUtilitiesAssessedCoalSeveranceSurtaxPenaltyandInterest
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Public Utilities, Costs to obtain additional ownership + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Public Utilities, Current Surface Mining Royalty Rate applied between 2000 and 2003 + References No definition available. + Details
Name: | pnm_PublicUtilitiesCurrentSurfaceMiningRoyaltyRateappliedbetween2000and2003
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Estimated Increase in Coal Cost, Percentage + References No definition available. + Details
Name: | pnm_PublicUtilitiesEstimatedIncreaseinCoalCostPercentage
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities,Estimated pre-tax regulatory disallowance + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Public Utilities, Estimated rate base value at 1/1/2018 + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Public Utilities, Estimated undepreciated value at 12/31/17 + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Public Utilities, Estimated Underpaid Surface Mining Royalties under proposed rate change + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Public Utilities,Estimated unrecoverable increase in operations and maintenance + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Public Utilities, Expected Funding Annual Requirements + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Public Utilities, Percentage of PNM Share of mining costs overbilled or unbilled, as ruled by arbitration, that will pass through FFPAC + References No definition available. + Details
Name: | pnm_PublicUtilitiesFFPACPercentageofminingcostsoverbilledorunbilledruledbyarbitration
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Government Standard Emission Limit + References No definition available. + Details
Name: | pnm_PublicUtilitiesGovernmentStandardEmissionLimit
Namespace Prefix: | pnm_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Insurance Recovery + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Public Utilities, Jointly Owned Utility Plant, Sale of Ownership Percentage + 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, Liability Insurance Coverage + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Public Utilities, Maximum Amount under Nuclear Electic Insurance Limited + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Public Utilities, Maximum Potential Assessment Per Incident + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Public Utilities, Newly Identified Replacement Gas-fired Generation, in Megawatts, December2013 + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Newly Identified Replacement Solar Generation, in Megawatts, December2013 + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | instant

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- Definition Public Utilities, Number of Compliance alternatives + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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

X
- Definition Public Utilities, Number of States To Address Regional Haze + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Overall Reduction Of Ownership, in Megawatts + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Ownership in Megawatts PNM has agreed not to obtain + References No definition available. + Details
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Data Type: | num:powerItemType
Balance Type: | na
Period Type: | instant

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- Definition Public Utilities, Ownership Percentage + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Ownership Percentage in Nuclear Reactor + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Ownership To Be Exchanged, in Megawatts + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Percentage capacity factor 7-year performance threshold + 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, Period over which to measure capacity performance + References No definition available. + Details
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- Definition Public Utilities, PNM Share Assessed Coal Severance Surtax Penalty and Interest to pass through FFPAC + References No definition available. + Details
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- Definition Public Utilities, PNM Share Estimated Underpaid Surface Mining Royalties under proposed rate change + References No definition available. + Details
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- Definition Public Utilities, PNM Share of arbitration ruling + References No definition available. + Details
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- Definition Public Utilities, Potential Acquisition of Ownership in Megawatts + References No definition available. + Details
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- Definition Public Utilities, Potential Capital Improvements billed as Mining Costs to SJGS Owners + References No definition available. + Details
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- Definition Public Utilities, Potential Overbilled Mining Costs SJCC Owes to SJGS Owners + References No definition available. + Details
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- Definition Public Utilities, Potential to emit tons per year of visibility impairing pollution, maximum + References No definition available. + Details
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- Definition Public Utilities, Potential Unbilled Mining Costs Owed to SJCC + References No definition available. + Details
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- Definition Public Utilities, Proposed Government Standard Emission Limit + References No definition available. + Details
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- Definition Public Utilities, Proposed reduction in carrying value + References No definition available. + Details
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- Definition Public Utilities, Proposed Retroactive Surface Mining Royalty Rate + References No definition available. + Details
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- Definition Public Utilities, Proposed value per Kilowatt effective January 1, 2018 + References No definition available. + Details
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- Definition Public Utilities, Recovery Percentage of Estimated undepreciated value at 12/31/17 + References No definition available. + Details
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- Definition Public Utilities, Requested Time Period to Recover Retired Units NBV + References No definition available. + Details
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- Definition Public Utilities, Revised SO2 Emissions Agreed Upon + References No definition available. + Details
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- Definition Public Utilities, Rule Imposes Opacity Limitation on Certain Fugitive Dust Emissions From Coal and Material Handling Operations + References No definition available. + Details
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- Definition Public Utilities, Sublimit Amount under Nuclear Electric Insurance Limited + References No definition available. + Details
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- Definition Public Utilities, Unsubscribed Ownership in Megawatts + References No definition available. + Details
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- Definition Public Utilities, Write-off Percentage of Estimated undepreciated value at 12/31/17 + References No definition available. + Details
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- Definition Public Utilitites, Plant Requirment to Meet Opacity Limit, Percentage + References No definition available. + Details
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- Definition Requested Additional Expenditure, Installation Capital Costs + References No definition available. + Details
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- Definition Requested Expenditure, Installation Capital Costs + References No definition available. + Details
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- Definition The fair value of investments held in a trust fund to pay for the costs of decontaminating and decommissioning facilities, whether such amount is presented as a separate caption or as a parenthetical disclosure on the balance sheet. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition The proportionate share of interest (percent) in a jointly owned utility plant. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 360 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 10.C) -URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 10 -Section C + Details
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- Details
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- Definition Amount of loss contingency liability. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349 + Details
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- Definition Reflects the estimated amount of loss from the specified contingency as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 9 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349 + Details
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- Definition Aggregate carrying amount, as of the balance sheet date, of current assets not separately disclosed in the balance sheet. Current assets are expected to be realized or consumed within one year (or the normal operating cycle, if longer). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.8) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 8 -Article 5 + Details
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- Definition The cash outflow for the purchase of investments that will be held in a decommissioning trust fund. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3213-108585 + Details
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