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Variable Interest Entities (Details) (USD $) | 3 Months Ended | 12 Months Ended | 6 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Dec. 31, 2014 | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Dec. 31, 2013 | Sep. 30, 2013 | Jun. 30, 2013 | Mar. 31, 2013 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Jul. 16, 2014 | Oct. 08, 2013 | May 30, 2008 MW | Jul. 17, 2014
Variable Interest Entity, Statement Of Operation [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Earnings Attributable to non-controlling interest |  |  |  |  |  |  |  |  | $ 14,127,000us-gaap_NetIncomeLossAttributableToNoncontrollingInterest | $ 14,521,000us-gaap_NetIncomeLossAttributableToNoncontrollingInterest | $ 14,050,000us-gaap_NetIncomeLossAttributableToNoncontrollingInterest |  |  |  |
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total current assets | 432,817,000us-gaap_AssetsCurrent |  |  |  | 401,539,000us-gaap_AssetsCurrent |  |  |  | 432,817,000us-gaap_AssetsCurrent | 401,539,000us-gaap_AssetsCurrent |  |  |  |  |
Total Assets | 5,829,325,000us-gaap_Assets |  |  |  | 5,500,210,000us-gaap_Assets |  |  |  | 5,829,325,000us-gaap_Assets | 5,500,210,000us-gaap_Assets | 5,372,583,000us-gaap_Assets |  |  |  |
Current liabilities | 704,282,000us-gaap_LiabilitiesCurrent |  |  |  | 492,671,000us-gaap_LiabilitiesCurrent |  |  |  | 704,282,000us-gaap_LiabilitiesCurrent | 492,671,000us-gaap_LiabilitiesCurrent |  |  |  |  |
Owners' equity - non-controlling interest | 73,546,000us-gaap_MinorityInterest |  |  |  | 77,029,000us-gaap_MinorityInterest |  |  |  | 73,546,000us-gaap_MinorityInterest | 77,029,000us-gaap_MinorityInterest |  |  |  |  |
Operating Leases, renewal options after original lease term |  |  |  |  |  |  |  |  | 6 years |  |  |  |  |  |
Earnings Attributable to PNMR | 18,992,000us-gaap_NetIncomeLoss | 55,653,000us-gaap_NetIncomeLoss | 29,141,000us-gaap_NetIncomeLoss | 12,468,000us-gaap_NetIncomeLoss | 7,648,000us-gaap_NetIncomeLoss | 54,555,000us-gaap_NetIncomeLoss | 27,678,000us-gaap_NetIncomeLoss | 10,626,000us-gaap_NetIncomeLoss | 116,254,000us-gaap_NetIncomeLoss | 100,507,000us-gaap_NetIncomeLoss | 105,547,000us-gaap_NetIncomeLoss |  |  |  |
Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating Leases, Currently active with trusts | 8pnm_OperatingLeasesCurrentlyActiveWithTrusts / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  | 8pnm_OperatingLeasesCurrentlyActiveWithTrusts / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |
Operating Leases, trust lessors | 8pnm_OperatingLeasesTrustLessors / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  | 8pnm_OperatingLeasesTrustLessors / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |
Operating Leases, Different institutional investors of trust lessors | 5pnm_OperatingLeasesDifferentInstitutionalInvestorsOfTrustLessors / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  | 5pnm_OperatingLeasesDifferentInstitutionalInvestorsOfTrustLessors / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |
Operating Leases, renewal options after original lease term |  |  |  |  |  |  |  |  | 2 years |  |  |  |  |  |
Operating Leases, Extended lease term option |  |  |  |  |  |  |  |  | 6 years |  |  |  |  |  |
Operating leases, future minimum payments due | 269,693,000us-gaap_OperatingLeasesFutureMinimumPaymentsDue / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  | 269,693,000us-gaap_OperatingLeasesFutureMinimumPaymentsDue / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |
Operating Leases, Future Minimum Payments Due, Current | 33,144,000us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |  | 33,144,000us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |
Earnings Attributable to PNMR | 13,955,000us-gaap_NetIncomeLoss / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 45,351,000us-gaap_NetIncomeLoss / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 20,346,000us-gaap_NetIncomeLoss / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 7,674,000us-gaap_NetIncomeLoss / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 2,639,000us-gaap_NetIncomeLoss / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 47,823,000us-gaap_NetIncomeLoss / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 26,124,000us-gaap_NetIncomeLoss / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 11,569,000us-gaap_NetIncomeLoss / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |  |
Valencia [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of mega watts purchased (in megawatts) |  |  |  |  |  |  |  |  |  |  |  |  |  | 158pnm_NumberOfMegaWattsPurchased / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |
Power plant total construction costs |  |  |  |  |  |  |  |  |  |  |  |  |  | 90,000,000pnm_PublicUtilitiesPowerPlantTotalConstructionCosts / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |
Long term contract for purchase of electric power fixed costs |  |  |  |  |  |  |  |  | 19,100,000pnm_LongTermContractForPurchaseOfElectricPowerFixedCosts / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | 18,900,000pnm_LongTermContractForPurchaseOfElectricPowerFixedCosts / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | 18,800,000pnm_LongTermContractForPurchaseOfElectricPowerFixedCosts / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  |
Long term contract for purchase of electric power variable charges |  |  |  |  |  |  |  |  | 1,200,000pnm_LongTermContractForPurchaseOfElectricPowerVariableCharges / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | 1,200,000pnm_LongTermContractForPurchaseOfElectricPowerVariableCharges / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | 900,000pnm_LongTermContractForPurchaseOfElectricPowerVariableCharges / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  |
Variable Interest Entity, Statement Of Operation [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Electric Revenue |  |  |  |  |  |  |  |  | 20,247,000pnm_ResultsOfOperationsVariableInterestEntityOperatingRevenues / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | 20,166,000pnm_ResultsOfOperationsVariableInterestEntityOperatingRevenues / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | 19,585,000pnm_ResultsOfOperationsVariableInterestEntityOperatingRevenues / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  |
Operating expenses |  |  |  |  |  |  |  |  | (6,120,000)pnm_ResultsOfOperationsVariableInterestEntityOperatingExpenses / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | (5,645,000)pnm_ResultsOfOperationsVariableInterestEntityOperatingExpenses / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | (5,535,000)pnm_ResultsOfOperationsVariableInterestEntityOperatingExpenses / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  |
Earnings Attributable to non-controlling interest |  |  |  |  |  |  |  |  | (14,127,000)us-gaap_NetIncomeLossAttributableToNoncontrollingInterest / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | (14,521,000)us-gaap_NetIncomeLossAttributableToNoncontrollingInterest / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | (14,050,000)us-gaap_NetIncomeLossAttributableToNoncontrollingInterest / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  |
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total current assets | 2,513,000us-gaap_AssetsCurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  | 2,658,000us-gaap_AssetsCurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  | 2,513,000us-gaap_AssetsCurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | 2,658,000us-gaap_AssetsCurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  |  |
Net property, plant and equipment | 72,321,000us-gaap_PropertyPlantAndEquipmentNet / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  | 75,137,000us-gaap_PropertyPlantAndEquipmentNet / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  | 72,321,000us-gaap_PropertyPlantAndEquipmentNet / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | 75,137,000us-gaap_PropertyPlantAndEquipmentNet / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  |  |
Total Assets | 74,834,000us-gaap_Assets / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  | 77,795,000us-gaap_Assets / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  | 74,834,000us-gaap_Assets / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | 77,795,000us-gaap_Assets / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  |  |
Current liabilities | 1,288,000us-gaap_LiabilitiesCurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  | 766,000us-gaap_LiabilitiesCurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  | 1,288,000us-gaap_LiabilitiesCurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | 766,000us-gaap_LiabilitiesCurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  |  |
Owners' equity - non-controlling interest | 73,546,000us-gaap_MinorityInterest / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  | 77,029,000us-gaap_MinorityInterest / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  | 73,546,000us-gaap_MinorityInterest / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | 77,029,000us-gaap_MinorityInterest / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  |  |
Long term contract option to purchase, purchase price - percentage of adjusted NBV |  |  |  |  |  |  |  |  | 50.00%pnm_LongtermcontractoptiontopurchasepurchasepricepercentageofadjustedNBV / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  |  |  |
Long term contract option to purchase, purchase price - percentage of FMV |  | 50.00%pnm_LongtermcontractoptiontopurchasepurchasepricepercentageofFMV / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  |  |  |  |  |  |  |  |  |  |
Long term contract option to purchase, number of days to set FMV |  |  |  |  |  |  |  |  | 60 days |  |  |  |  |  |
Long term contract option to purchase, estimated purchase price |  |  |  |  |  |  |  |  |  |  |  |  | 85,000,000pnm_Longtermcontractoptiontopurchaseestimatedpurchaseprice / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |
Long term contract option to purchase, approximate approval period |  |  |  |  |  |  |  |  | 15 months |  |  |  |  |  |
Long term contract option to purchase, ownership percentage |  |  |  |  |  |  |  |  | 50.00%pnm_Longtermcontractoptiontopurchaseownershippercentage / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  |  |  |
Long Term Contract For Purchase of Power Term of Contract |  |  |  |  |  |  |  |  | 20 years |  |  |  |  |  |
Valencia [Member] | Maximum [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Jointly owned utility plant, option to purchase proportionate ownership share | 50.00%pnm_JointlyOwnedUtilityPlantOptionToPurchaseProportionateOwnershipShare / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  |  |  |  |  | 50.00%pnm_JointlyOwnedUtilityPlantOptionToPurchaseProportionateOwnershipShare / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |  |  |  |
Delta [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long term contract for purchase of electric power fixed costs |  |  |  |  |  |  |  |  |  |  |  | 3,500,000pnm_LongTermContractForPurchaseOfElectricPowerFixedCosts / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = pnm_DeltaMember |  |  |
Long term contract for purchase of electric power variable charges |  |  |  |  |  |  |  |  |  |  |  | 600,000pnm_LongTermContractForPurchaseOfElectricPowerVariableCharges / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = pnm_DeltaMember |  |  |
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period of Long Term Contract For Purchase of Electric Power Fixed Costs |  |  |  |  |  |  |  |  | 20 years |  |  |  |  |  |
PVNGS [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating leases, future minimum payments due | 20,300,000us-gaap_OperatingLeasesFutureMinimumPaymentsDue / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember |  |  |  |  |  |  |  | 20,300,000us-gaap_OperatingLeasesFutureMinimumPaymentsDue / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember |  |  |  |  |  |
Operating leases, future minimum payments due, renewal term | 145,200,000pnm_Operatingleasesfutureminimumpaymentsduerenewalterm / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember |  |  |  |  |  |  |  | 145,200,000pnm_Operatingleasesfutureminimumpaymentsduerenewalterm / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember |  |  |  |  |  |
Delta [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long term contract for purchase of electric power fixed costs |  |  |  |  |  |  |  |  |  | 6,400,000pnm_LongTermContractForPurchaseOfElectricPowerFixedCosts / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityVIEOrPotentialVIEInformationUnavailabilityMember | 6,200,000pnm_LongTermContractForPurchaseOfElectricPowerFixedCosts / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityVIEOrPotentialVIEInformationUnavailabilityMember |  |  |  |
Long term contract for purchase of electric power variable charges |  |  |  |  |  |  |  |  |  | 1,800,000pnm_LongTermContractForPurchaseOfElectricPowerVariableCharges / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityVIEOrPotentialVIEInformationUnavailabilityMember | 800,000pnm_LongTermContractForPurchaseOfElectricPowerVariableCharges / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityVIEOrPotentialVIEInformationUnavailabilityMember |  |  |  |
Delta [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to acquire businesses, net |  |  |  |  |  |  |  |  |  |  |  | 22,800,000pnm_Paymentstoacquirebusinessesnet / us-gaap_BusinessAcquisitionAxis = pnm_DeltaMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 14,600,000us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLongTermDebt / us-gaap_BusinessAcquisitionAxis = pnm_DeltaMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 58,100,000us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = pnm_DeltaMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Business Combination, recognized identifiable assets acquired, accumulated amort |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 23,500,000pnm_BusinessCombinationrecognizedidentifiableassetsacquiredaccumulatedamort / us-gaap_BusinessAcquisitionAxis = pnm_DeltaMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3,600,000us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssets / us-gaap_BusinessAcquisitionAxis = pnm_DeltaMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3,400,000us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentAssets / us-gaap_BusinessAcquisitionAxis = pnm_DeltaMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 300,000us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities / us-gaap_BusinessAcquisitionAxis = pnm_DeltaMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3,400,000us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilities / us-gaap_BusinessAcquisitionAxis = pnm_DeltaMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Palo Verde Nuclear Generating Station [Member] | PVNGS [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
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