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Income Taxes Carryforwards (Details) (USD $)
 1 Months Ended 12 Months Ended
May 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Operating Loss Carryforwards [Line Items]        
Additional Income Tax Expense, Impairment of NM Wind Credits     $ 2,400,000pnm_AdditionalIncomeTaxExpenseImpairmentofNMWindCredits $ 700,000pnm_AdditionalIncomeTaxExpenseImpairmentofNMWindCredits
Deferred Tax Assets, Operating Loss Carryforwards, State and Local, Decrease     1,500,000pnm_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocalDecrease  
New Mexico Corporate tax rate, current   7.60%pnm_NewMexicoCorporatetaxratecurrent    
New Mexico Corporate tax rate, 2014   5.90%pnm_NewMexicoCorporatetaxrate2014    
Increase in regulatory liabilities due to change in state corporate tax rate     23,900,000pnm_Increaseinregulatoryliabilitiesduetochangeinstatecorporatetaxrate  
Increase in income tax expense due to change in state corporate tax rate     1,200,000pnm_Increaseinincometaxexpenseduetochangeinstatecorporatetaxrate  
Decrease in regulatory liabilities due to change in state corporate tax rate   (4,600,000)pnm_Decreaseinregulatoryliabilitiesduetochangeinstatecorporatetaxrate    
Decrease in deferred tax asset due to change in state corporate tax rate   200,000pnm_Decreaseindeferredtaxassetduetochangeinstatecorporatetaxrate    
Investment tax credit, Impairment   900,000pnm_InvestmenttaxcreditImpairment    
State Net Operating Loss Carryforward, Impairment   3,100,000pnm_StateNetOperatingLossCarryforwardImpairment    
Deferred Tax Assets, Valuation Allowance   5,500,000us-gaap_DeferredTaxAssetsValuationAllowance    
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount   900,000us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount 3,900,000us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount 700,000us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount
Federal Tax Refund 96,200,000pnm_FederalTaxRefund      
New Accounting Pronouncements Not Yet Adopted, Effect on Deferred Tax Asset     19,900,000pnm_NewAccountingPronouncementsNotYetAdoptedEffectonDeferredTaxAsset  
Income Taxes   69,738,000us-gaap_IncomeTaxExpenseBenefit 59,513,000us-gaap_IncomeTaxExpenseBenefit 54,910,000us-gaap_IncomeTaxExpenseBenefit
Internal Revenue Service (IRS) [Member]        
Operating Loss Carryforwards [Line Items]        
Federal Net Operating Loss Carryforwards to Expire in 2030   405,700,000us-gaap_OperatingLossCarryforwards
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_InternalRevenueServiceIRSMember		    
Federal Tax Credit Carryforwards that Expire Beginning in 2023   54,700,000pnm_FederalTaxCreditCarryforwardsThatExpireBeginningIn2023
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_InternalRevenueServiceIRSMember		    
Internal Revenue Service (IRS) [Member]        
Operating Loss Carryforwards [Line Items]        
Income Taxes   (1,300,000)us-gaap_IncomeTaxExpenseBenefit
/ us-gaap_IncomeTaxAuthorityNameAxis
= us-gaap_InternalRevenueServiceIRSMember		    
Public Service Company of New Mexico [Member]        
Operating Loss Carryforwards [Line Items]        
Increase in deferred tax asset not related to regulatory activity, as a result of tax rate change   100,000pnm_Increaseindeferredtaxassetnotrelatedtoregulatoryactivityasaresultoftaxratechange
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember		    
Decrease in income tax expense due to tax rate change   300,000pnm_Decreaseinincometaxexpenseduetotaxratechange
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember		    
State Net Operating Loss Carryforward, Impairment   1,000,000pnm_StateNetOperatingLossCarryforwardImpairment
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember		    
Federal Tax Refund 77,400,000pnm_FederalTaxRefund
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember		      
New Accounting Pronouncements Not Yet Adopted, Effect on Deferred Tax Asset     11,200,000pnm_NewAccountingPronouncementsNotYetAdoptedEffectonDeferredTaxAsset
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember		  
Income Taxes   52,633,000us-gaap_IncomeTaxExpenseBenefit
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember		 48,804,000us-gaap_IncomeTaxExpenseBenefit
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember		 50,713,000us-gaap_IncomeTaxExpenseBenefit
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember
Public Service Company of New Mexico [Member] | Internal Revenue Service (IRS) [Member]        
Operating Loss Carryforwards [Line Items]        
Income Taxes   1,100,000us-gaap_IncomeTaxExpenseBenefit
/ us-gaap_IncomeTaxAuthorityNameAxis
= us-gaap_InternalRevenueServiceIRSMember
/ dei_LegalEntityAxis
= pnm_PublicServiceCompanyOfNewMexicoMember		    
PNM and TNMP [Domain]        
Operating Loss Carryforwards [Line Items]        
Deferred Tax Assets, Valuation Allowance   0us-gaap_DeferredTaxAssetsValuationAllowance
/ dei_LegalEntityAxis
= pnm_PNMandTNMPDomain		    
Other Subsidiaries [Member]        
Operating Loss Carryforwards [Line Items]        
State Net Operating Loss Carryforward, Impairment   2,100,000pnm_StateNetOperatingLossCarryforwardImpairment
/ dei_LegalEntityAxis
= pnm_OtherSubsidiariesMember		    
Texas-New Mexico Power Company [Member]        
Operating Loss Carryforwards [Line Items]        
New Accounting Pronouncements Not Yet Adopted, Effect on Deferred Tax Asset     6,800,000pnm_NewAccountingPronouncementsNotYetAdoptedEffectonDeferredTaxAsset
/ dei_LegalEntityAxis
= pnm_TexasNewMexicoPowerCompanyMember		  
Income Taxes   22,523,000us-gaap_IncomeTaxExpenseBenefit
/ dei_LegalEntityAxis
= pnm_TexasNewMexicoPowerCompanyMember		 17,621,000us-gaap_IncomeTaxExpenseBenefit
/ dei_LegalEntityAxis
= pnm_TexasNewMexicoPowerCompanyMember		 15,352,000us-gaap_IncomeTaxExpenseBenefit
/ dei_LegalEntityAxis
= pnm_TexasNewMexicoPowerCompanyMember
PNM Resources [Member]        
Operating Loss Carryforwards [Line Items]        
Income Taxes   (5,389,000)us-gaap_IncomeTaxExpenseBenefit
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember		 (6,870,000)us-gaap_IncomeTaxExpenseBenefit
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember		 (11,168,000)us-gaap_IncomeTaxExpenseBenefit
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
PNM Resources [Member] | Internal Revenue Service (IRS) [Member]        
Operating Loss Carryforwards [Line Items]        
Income Tax Examination, Liability (Refund) Adjustment from Settlement with Taxing Authority   (2,000,000)us-gaap_IncomeTaxExaminationLiabilityRefundAdjustmentFromSettlementWithTaxingAuthority
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_InternalRevenueServiceIRSMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember		    
Income Taxes   $ (200,000)us-gaap_IncomeTaxExpenseBenefit
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_InternalRevenueServiceIRSMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember