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Commitments and Contingencies - National Ambient Air Quality Standards (Details) (Public Service Company of New Mexico [Member])
 0 Months Ended
Mar. 02, 2015
Nov. 25, 2014
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Jan. 31, 2010
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Mar. 31, 2015
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Nov. 08, 2013
National Ambient Air Quality Standards, 2015 EPA Legal Settlement [Member]
          
Public Utilities, Commitments And Contingencies [Line Items]          
Period of time to act on settlement 16 months        
Public Utilities, Emissions Tons of SO2 per year 16,000pnm_PublicUtilitiesEmissionsTonsofSO2peryear
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_NationalAmbientAirQualityStandards2015EPALegalSettlementMember
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember		        
Minimum [Member] | National Ambient Air Quality Standards, 2015 EPA Legal Settlement [Member]
          
Public Utilities, Commitments And Contingencies [Line Items]          
Public Utilities, Emissions Tons of SO2 per year 2,600pnm_PublicUtilitiesEmissionsTonsofSO2peryear
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_NationalAmbientAirQualityStandards2015EPALegalSettlementMember
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		        
Public Utilities, 1-hour SO2 Emissions Rate 0.45pnm_PublicUtilities1hourSO2EmissionsRate
/ pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis
= pnm_NationalAmbientAirQualityStandards2015EPALegalSettlementMember
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		        
San Juan Generating Station And Four Corners [Member] | Minimum [Member]
          
Public Utilities, Commitments And 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		    
San Juan Generating Station And Four Corners [Member] | Maximum [Member]
          
Public Utilities, Commitments And Contingencies [Line Items]          
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 Utilities, Government Standard Emission Limit       75pnm_PublicUtilitiesGovernmentStandardEmissionLimit
/ us-gaap_JointlyOwnedUtilityPlantAxis
= pnm_SanJuanGeneratingStationAndFourCornersMember
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		  
San Juan Generating Station [Member] | National Ambient Air Quality Standards [Member]          
Public Utilities, Commitments And 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