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v2.4.1.9

Pension and Other Postretirement Benefits Narrative (Details) (USD $) | 12 Months Ended | 1 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Jan. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Expected return on plan assets | 4.00%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets |  |  |
Defined Benefit Plans, Gains and losses that lie outside the corridor, amortized (in years) | 5 years |  |  |
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent | 75.00%us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent |  |  |
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay | 6.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent |  |  |
Pension Plan [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Expected long-term return resulting from effect of one-percentage point decrease (as a percent) | 1.00%pnm_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnResultingFromEffectOfOnePercentagePointDecrease / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |
Expected long-term return resulting from effect of one-percentage point increase (as a percent) | 1.00%pnm_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnResultingFromEffectOfOnePercentagePointIncrease / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |
Other Postretirement Benefits [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Expected long-term return resulting from effect of one-percentage point decrease (as a percent) | 1.00%pnm_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnResultingFromEffectOfOnePercentagePointDecrease / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  |  |
Public Service Company of New Mexico [Member] | Pension Plan [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Expected return on plan assets | 7.20%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 7.65%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 8.25%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |
Defined Benefit Plan, Other Changes | 50,600,000us-gaap_DefinedBenefitPlanOtherChanges / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | $ (60,900,000)us-gaap_DefinedBenefitPlanOtherChanges / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |
Defined Benefit Plan, Actuarial Gain (Loss) resulting from changes in demographics and other trends | (200,000)pnm_DefinedBenefitPlanActuarialGainLossresultingfromchangesindemographicsandothertrends / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | (4,400,000)pnm_DefinedBenefitPlanActuarialGainLossresultingfromchangesindemographicsandothertrends / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |
Defined Benefit Plan, Actuarial Gain (Loss) resulting from changes in other assumptions and experience | 200,000pnm_DefinedBenefitPlanActuarialGainLossresultingfromchangesinotherassumptionsandexperience / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 100,000pnm_DefinedBenefitPlanActuarialGainLossresultingfromchangesinotherassumptionsandexperience / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |
Actual plan asset allocations (as a percent) | 14.30%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |
Expected Long-term return on assets decrease resulting in increase net periodic costs In next fiscal year | 5,800,000pnm_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssetsDecreaseResultingInIncreaseNetPeriodicCostsInNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |
Employer contributions | 0us-gaap_DefinedBenefitPlanContributionsByEmployer / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 60,000,000us-gaap_DefinedBenefitPlanContributionsByEmployer / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |
Estimated future employer contributions from 2013-2017 | 22,000,000pnm_DefinedBenefitPlanEstimatedFutureEmployerContributionsInYearTwoThroughYearFour / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax | (34,345,000)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |
Public Service Company of New Mexico [Member] | Other Postretirement Benefits [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Expected return on plan assets | 8.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 8.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 8.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |
Defined Benefit Plan, Other Changes | 6,700,000us-gaap_DefinedBenefitPlanOtherChanges / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | (8,800,000)us-gaap_DefinedBenefitPlanOtherChanges / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |
Defined Benefit Plan, Actuarial Gain (Loss) resulting from changes in demographics and other trends | 5,400,000pnm_DefinedBenefitPlanActuarialGainLossresultingfromchangesindemographicsandothertrends / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | (4,200,000)pnm_DefinedBenefitPlanActuarialGainLossresultingfromchangesindemographicsandothertrends / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |
Actual plan asset allocations (as a percent) | 10.20%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |
Expected Long-term return on assets decrease resulting in increase net periodic costs In next fiscal year | 700,000pnm_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssetsDecreaseResultingInIncreaseNetPeriodicCostsInNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |
Employer contributions | 3,532,000us-gaap_DefinedBenefitPlanContributionsByEmployer / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 3,576,000us-gaap_DefinedBenefitPlanContributionsByEmployer / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax | (2,800,000)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |
Estimated future employer contributions in next fiscal year | 3,500,000us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |
Defined Benefit Plan, Estimated Future Employer Contributions in Year Two Through Year Five | 14,000,000pnm_DefinedBenefitPlanEstimatedFutureEmployerContributionsinYearTwoThroughYearFive / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |
Texas-New Mexico Power Company [Member] | Pension Plan [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Expected return on plan assets | 7.20%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | 7.65%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | 8.25%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember |
Defined Benefit Plan, Other Changes | 5,100,000us-gaap_DefinedBenefitPlanOtherChanges / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | (6,400,000)us-gaap_DefinedBenefitPlanOtherChanges / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember |  |
Defined Benefit Plan, Actuarial Gain (Loss) resulting from changes in demographics and other trends | 400,000pnm_DefinedBenefitPlanActuarialGainLossresultingfromchangesindemographicsandothertrends / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | 1,400,000pnm_DefinedBenefitPlanActuarialGainLossresultingfromchangesindemographicsandothertrends / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember |  |
Defined Benefit Plan, Actuarial Gain (Loss) resulting from changes in other assumptions and experience | (1,300,000)pnm_DefinedBenefitPlanActuarialGainLossresultingfromchangesinotherassumptionsandexperience / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | (100,000)pnm_DefinedBenefitPlanActuarialGainLossresultingfromchangesinotherassumptionsandexperience / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember |  |
Actual plan asset allocations (as a percent) | 13.50%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember |  |  |
Expected Long-term return on assets decrease resulting in increase net periodic costs In next fiscal year | 600,000pnm_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssetsDecreaseResultingInIncreaseNetPeriodicCostsInNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember |  |  |
Employer contributions | 0us-gaap_DefinedBenefitPlanContributionsByEmployer / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | 1,000,000us-gaap_DefinedBenefitPlanContributionsByEmployer / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember |  |
Estimated future employer contributions from 2013-2017 | 0pnm_DefinedBenefitPlanEstimatedFutureEmployerContributionsInYearTwoThroughYearFour / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember |  |  |
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax | (4,420,000)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember |  |  |
Texas-New Mexico Power Company [Member] | Other Postretirement Benefits [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Expected return on plan assets | 6.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | 6.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | 6.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember |
Defined Benefit Plan, Other Changes | 1,100,000us-gaap_DefinedBenefitPlanOtherChanges / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | (1,300,000)us-gaap_DefinedBenefitPlanOtherChanges / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember |  |
Defined Benefit Plan, Actuarial Gain (Loss) resulting from changes in demographics and other trends | (100,000)pnm_DefinedBenefitPlanActuarialGainLossresultingfromchangesindemographicsandothertrends / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | (200,000)pnm_DefinedBenefitPlanActuarialGainLossresultingfromchangesindemographicsandothertrends / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember |  |
Actual plan asset allocations (as a percent) | 8.90%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember |  |  |
Expected Long-term return on assets decrease resulting in increase net periodic costs In next fiscal year | 100,000pnm_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssetsDecreaseResultingInIncreaseNetPeriodicCostsInNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember |  |  |
Employer contributions | 343,000us-gaap_DefinedBenefitPlanContributionsByEmployer / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | 342,000us-gaap_DefinedBenefitPlanContributionsByEmployer / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember |  |
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax | (1,300,000)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember |  |  |
Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates, Net periodic expense and APBO | 0pnm_EffectofOnePercentagePointChangeinAssumedHealthCareCostTrendRatesNetperiodicexpenseandAPBO / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember |  |  |
Estimated future employer contributions in next fiscal year | 300,000us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember |  |  |
Defined Benefit Plan, Estimated Future Employer Contributions in Year Two Through Year Five | 1,400,000pnm_DefinedBenefitPlanEstimatedFutureEmployerContributionsinYearTwoThroughYearFive / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember |  |  |
PNM and TNMP [Domain] | Other Postretirement Benefits [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax | 0us-gaap_DefinedBenefitPlanAmountsRecognizedInOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PNMandTNMPDomain |  |  |
Equity Securities [Member] | Pension Plan [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target plan asset allocations (as a percent) | 21.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquitySecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |
Equity Securities [Member] | Other Postretirement Benefits [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target plan asset allocations (as a percent) | 70.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquitySecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  |  |
Debt Securities [Member] | Pension Plan [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target plan asset allocations (as a percent) | 65.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_DebtSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |
Debt Securities [Member] | Other Postretirement Benefits [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target plan asset allocations (as a percent) | 30.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_DebtSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  |  |
Alternative Investments [Member] | Pension Plan [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Target plan asset allocations (as a percent) | 14.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = pnm_AlternativeInvestmentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |
Minimum [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Defined Contribution Plan, non matching contribution of eligible compensation based on eligible employee's age | 3.00%pnm_DefinedContributionPlanNonMatchingContributionOfEligibleCompensationBasedOnEligibleEmployeesAge / us-gaap_RangeAxis = us-gaap_MinimumMember |  |  |
Minimum [Member] | Pension Plan [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
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