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Commitments and Contingencies - Litigation and Rulemaking (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Dec. 21, 2011
mw
Public Utilities, Commitments And Contingencies [Line Items]    
Minimum Megawatt Capacity from Coal and Oil-Fired Electric Generating Units under Jurisdiction of the Mercury and Air Toxics Standards   25pnm_MinimumMegawattCapacityfromCoalandOilFiredElectricGeneratingUnitsunderJurisdictionoftheMercuryandAirToxicsStandards
San Juan Generating Station [Member]    
Public Utilities, Commitments And Contingencies [Line Items]    
Mercury Removal Rate, Percentage   99.00%pnm_MercuryRemovalRatePercentage
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_SanJuanGeneratingStationMember
Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] | Mercury Control [Member]    
Public Utilities, Commitments And Contingencies [Line Items]    
Current Annual Mercury Control Costs $ 0.7pnm_CurrentAnnualMercuryControlCosts
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_MercuryControlMember
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_SanJuanGeneratingStationMember
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember		  
Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] | Maximum [Member] | Mercury Control [Member]    
Public Utilities, Commitments And Contingencies [Line Items]    
Contingent Estimated Annual Mercury Control Cost $ 6.6pnm_ContingentEstimatedAnnualMercuryControlCost
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_MercuryControlMember
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_SanJuanGeneratingStationMember
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember