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Commitments and Contingencies - Four Corners (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2013
Mar. 31, 2015
Aug. 06, 2012
compliance_alternative
Four Corners [Member]      
Public Utilities, Commitments And Contingencies [Line Items]      
Public Utilities, Jointly Owned Utility Plant, Sale of Ownership Percentage 48.00%pnm_PublicUtilitiesJointlyOwnedUtilityPlantSaleofOwnershipPercentage
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_FourCornersMember		    
Clean Air Act Related to Post Combustion Controls [Member] | Public Service Company of New Mexico [Member] | Four Corners [Member]      
Public Utilities, Commitments And Contingencies [Line Items]      
Public Utilities, Number of Compliance alternatives     2pnm_PublicUtilitiesNumberOfComplianceAlternatives
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_CleanAirActRelatedToPostCombustionControlsMember
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_FourCornersMember
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
Public Utilities, Plant Requirement to Meet NOx emissions Limit   0.015pnm_PublicUtilitiesPlantRequirementtoMeetNOxemissionsLimit
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_CleanAirActRelatedToPostCombustionControlsMember
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_FourCornersMember
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember		  
Public Utilities, Plant Requirement to Meet Opacity Limit, Percentage   20.00%pnm_PublicUtilitiesPlantRequirementtoMeetOpacityLimitPercentage
/ 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		  
Loss Contingency, Estimate of Possible Loss   $ 83.9us-gaap_LossContingencyEstimateOfPossibleLoss
/ 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]      
Public Utilities, Commitments And Contingencies [Line Items]      
Public Utilities, Ownership Percentage   13.00%pnm_PublicUtilitiesOwnershipPercentage
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_CleanAirActRelatedToPostCombustionControlsMember
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_FourCornersUnits4And5CoalMember
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember