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Regulatory and Rate Matters - Renewable Portfolio Standard and Energy Rider (Details) (Public Service Company of New Mexico [Member], USD $)
 3 Months Ended 12 Months Ended
Mar. 31, 2015
MWh
Dec. 31, 2013
Dec. 31, 2014
MWh
Renewable Portfolio Standard [Member] | Required Percentage by 2011 [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Required Percentage of Renewable Energy in Portfolio to Electric Sales 10.00%pnm_PublicUtilitiesRequiredPercentageOfRenewableEnergyInPortfolioToElectricSales
/ pnm_DateOfRegulatoryActionAxis
= pnm_RequiredPercentageBy2011Member
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewablePortfolioStandardMember		    
Renewable Portfolio Standard [Member] | Required Percentage by 2015 [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Required Percentage of Renewable Energy in Portfolio to Electric Sales 15.00%pnm_PublicUtilitiesRequiredPercentageOfRenewableEnergyInPortfolioToElectricSales
/ pnm_DateOfRegulatoryActionAxis
= pnm_RequiredPercentageBy2015Member
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewablePortfolioStandardMember		    
Renewable Portfolio Standard [Member] | Required Percentage by 2020 [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Required Percentage of Renewable Energy in Portfolio to Electric Sales 20.00%pnm_PublicUtilitiesRequiredPercentageOfRenewableEnergyInPortfolioToElectricSales
/ pnm_DateOfRegulatoryActionAxis
= pnm_RequiredPercentageBy2020Member
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewablePortfolioStandardMember		    
2014 Wind generated Renewable Energy Credits [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Number of Mega Watt Hours of Wind Generation 50,000pnm_PublicUtilitiesNumberofMegaWattHoursofWindGeneration
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_A2014WindgeneratedRenewableEnergyCreditsMember		    
Renewable Portfolio Standard 2014 [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Final Cost of Solar Photovoltaic Capacity   $ 46,500,000pnm_PublicUtilitiesFinalCostofSolarPhotovoltaicCapacity
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewablePortfolioStandard2014Member		  
Public Utilities, Number of Mega Watts of Solar Photovoltaic Capacity 23pnm_PublicUtilitiesNumberOfMegaWattsOfSolarPhotovoltaicCapacity
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewablePortfolioStandard2014Member		    
Public Utilities, Estimated Cost of Mega Watts of Solar Photovoltaic Capacity 46,700,000pnm_PublicUtilitiesEstimatedCostOfMegaWattsOfSolarPhotovoltaicCapacity
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewablePortfolioStandard2014Member		    
Public Utilities, Wind Capacity Planned Purchase Agreement Term 20 years    
Public Utilities, Number of Mega Watts of Wind Energy Capacity 102pnm_PublicUtilitiesNumberofMegaWattsofWindEnergyCapacity
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewablePortfolioStandard2014Member		    
Public Utilities, First Year Cost of Wind Capacity Planned Purchase Agreement 5,800,000.0pnm_PublicUtilitiesFirstYearCostofWindCapacityPlannedPurchaseAgreement
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewablePortfolioStandard2014Member		    
2015 Wind generated Renewable Energy Credits [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Number of Mega Watt Hours of Wind Generation 120,000pnm_PublicUtilitiesNumberofMegaWattHoursofWindGeneration
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_A2015WindgeneratedRenewableEnergyCreditsMember		    
Renewable Portfolio Standard 2015 [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Number of Mega Watts of Solar Photovoltaic Capacity 40pnm_PublicUtilitiesNumberOfMegaWattsOfSolarPhotovoltaicCapacity
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewablePortfolioStandard2015Member		    
Public Utilities, Estimated Cost of Mega Watts of Solar Photovoltaic Capacity 79,300,000pnm_PublicUtilitiesEstimatedCostOfMegaWattsOfSolarPhotovoltaicCapacity
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewablePortfolioStandard2015Member		    
Public Utilities, Approved Revised cost per MWh for additional necessary procurements to comply with RPS     3.00pnm_PublicUtilitiesApprovedRevisedcostperMWhforadditionalnecessaryprocurementstocomplywithRPS
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewablePortfolioStandard2015Member
Public Utilities, Number of MegaWatt Hours of renewable resources     44,000pnm_PublicUtilitiesNumberofMegaWattHoursofrenewableresources
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewablePortfolioStandard2015Member
Public Utilities, Actual cost per MWh for additional necessary procurements to comply with RPS     1.75pnm_PublicUtilitiesActualcostperMWhforadditionalnecessaryprocurementstocomplywithRPS
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewablePortfolioStandard2015Member
Renewable Energy Rider [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Revenue from Renewable energy rider     34,300,000pnm_PublicUtilitiesRevenuefromRenewableenergyrider
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewableEnergyRiderMember
Minimum [Member] | Wind Energy [Member] | Renewable Portfolio Standard [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Required Percentage of Diversification 30.00%pnm_PublicUtilitiesRequiredPercentageOfDiversification
/ pnm_DiversificationByTypeAxis
= pnm_WindEnergyMember
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewablePortfolioStandardMember		    
Minimum [Member] | Solar Energy [Member] | Renewable Portfolio Standard [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Required Percentage of Diversification 20.00%pnm_PublicUtilitiesRequiredPercentageOfDiversification
/ pnm_DiversificationByTypeAxis
= pnm_SolarEnergyMember
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewablePortfolioStandardMember		    
Minimum [Member] | Renewable Technologies [Member] | Renewable Portfolio Standard [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Required Percentage of Diversification 5.00%pnm_PublicUtilitiesRequiredPercentageOfDiversification
/ pnm_DiversificationByTypeAxis
= pnm_RenewableTechnologiesMember
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewablePortfolioStandardMember		    
Minimum [Member] | Distributed Generation [Member] | Renewable Portfolio Standard [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Required Percentage of Diversification 3.00%pnm_PublicUtilitiesRequiredPercentageOfDiversification
/ pnm_DiversificationByTypeAxis
= pnm_DistributedGenerationMember
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewablePortfolioStandardMember		    
Maximum [Member] | Renewable Portfolio Standard [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Reasonable Cost Threshold 3.00%pnm_PublicUtilitiesReasonableCostThreshold
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewablePortfolioStandardMember		    
Maximum [Member] | Renewable Energy Rider [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Rider Condition of Earned Return on Jurisdictional Equity in 2013 10.50%pnm_PublicUtilitiesRiderConditionOfEarnedReturnOnJurisdictionalEquityIn2013
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewableEnergyRiderMember		 10.50%pnm_PublicUtilitiesRiderConditionOfEarnedReturnOnJurisdictionalEquityIn2013
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewableEnergyRiderMember		  
Public Utilities, Annual Revenue To be Collected Under 2015 Rider Rate 44,700,000pnm_PublicUtilitiesAnnualRevenueTobeCollectedUnder2015RiderRate
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewableEnergyRiderMember		    
Public Utilities, Revised Annual Revenue To be Collected Under 2015 Rider Rate 43,000,000pnm_PublicUtilitiesRevisedAnnualRevenueTobeCollectedUnder2015RiderRate
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ pnm_ScheduleOfRegulatoryRateMattersAxis
= pnm_RenewableEnergyRiderMember