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Regulatory Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Regulatory Assets |  |
Regulatory Assets, Current | $ 47,855us-gaap_RegulatoryAssetsCurrent | $ 24,416us-gaap_RegulatoryAssetsCurrent
Regulatory Assets, Noncurrent | 491,007us-gaap_RegulatoryAssetsNoncurrent | 523,955us-gaap_RegulatoryAssetsNoncurrent
Regulatory Liabilities |  |
Regulatory Liability, Current | (1,703)us-gaap_RegulatoryLiabilityCurrent | (1,081)us-gaap_RegulatoryLiabilityCurrent
Regulatory liabilities, Noncurrent | (466,143)us-gaap_RegulatoryLiabilityNoncurrent | (460,649)us-gaap_RegulatoryLiabilityNoncurrent
Public Service Company of New Mexico [Member] |  |
Regulatory Assets |  |
Regulatory Assets, Current | 43,980us-gaap_RegulatoryAssetsCurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 19,394us-gaap_RegulatoryAssetsCurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Regulatory Assets, Noncurrent | 357,045us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 384,217us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Regulatory Assets | 401,025us-gaap_RegulatoryAssets / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 403,611us-gaap_RegulatoryAssets / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Regulatory Liabilities |  |
Regulatory Liability, Current | (1,703)us-gaap_RegulatoryLiabilityCurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | (1,081)us-gaap_RegulatoryLiabilityCurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Regulatory liabilities, Noncurrent | (425,481)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | (414,611)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Regulatory Liabilities | (427,184)us-gaap_RegulatoryLiabilities / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | (415,692)us-gaap_RegulatoryLiabilities / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Texas-New Mexico Power Company [Member] |  |
Regulatory Assets |  |
Regulatory Assets, Current | 3,875us-gaap_RegulatoryAssetsCurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | 5,022us-gaap_RegulatoryAssetsCurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Regulatory Assets, Noncurrent | 133,962us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | 139,738us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Regulatory Assets | 137,837us-gaap_RegulatoryAssets / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | 144,760us-gaap_RegulatoryAssets / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Regulatory Liabilities |  |
Regulatory liabilities, Noncurrent | (40,662)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | (46,038)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Removal Costs [Member] | Public Service Company of New Mexico [Member] |  |
Regulatory Liabilities |  |
Regulatory liabilities, Noncurrent | (277,148)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryLiabilityAxis = us-gaap_RemovalCostsMember | (266,075)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryLiabilityAxis = us-gaap_RemovalCostsMember
Removal Costs [Member] | Texas-New Mexico Power Company [Member] |  |
Regulatory Liabilities |  |
Regulatory liabilities, Noncurrent | (29,391)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryLiabilityAxis = us-gaap_RemovalCostsMember | (30,863)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryLiabilityAxis = us-gaap_RemovalCostsMember
Deferred Income Tax Charge [Member] | Public Service Company of New Mexico [Member] |  |
Regulatory Liabilities |  |
Regulatory liabilities, Noncurrent | (75,941)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryLiabilityAxis = us-gaap_DeferredIncomeTaxChargesMember | (80,495)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryLiabilityAxis = us-gaap_DeferredIncomeTaxChargesMember
Deferred Income Tax Charge [Member] | Texas-New Mexico Power Company [Member] |  |
Regulatory Liabilities |  |
Regulatory liabilities, Noncurrent | (3,923)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryLiabilityAxis = us-gaap_DeferredIncomeTaxChargesMember | (4,563)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryLiabilityAxis = us-gaap_DeferredIncomeTaxChargesMember
Asset Retirement Obligation Costs [Member] | Public Service Company of New Mexico [Member] |  |
Regulatory Liabilities |  |
Regulatory liabilities, Noncurrent | (35,834)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryLiabilityAxis = us-gaap_AssetRetirementObligationCostsMember | (37,567)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryLiabilityAxis = us-gaap_AssetRetirementObligationCostsMember
Renewable Energy Program [Member] | Public Service Company of New Mexico [Member] |  |
Regulatory Liabilities |  |
Regulatory liabilities, Noncurrent | (24,854)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryLiabilityAxis = us-gaap_RenewableEnergyProgramMember | (26,011)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryLiabilityAxis = us-gaap_RenewableEnergyProgramMember
Other Regulatory Assets (Liabilities) [Member] | Public Service Company of New Mexico [Member] |  |
Regulatory Liabilities |  |
Regulatory liabilities, Noncurrent | (11,704)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryLiabilityAxis = us-gaap_OtherRegulatoryAssetsLiabilitiesMember | (4,463)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryLiabilityAxis = us-gaap_OtherRegulatoryAssetsLiabilitiesMember
Other Regulatory Assets (Liabilities) [Member] | Texas-New Mexico Power Company [Member] |  |
Regulatory Liabilities |  |
Regulatory liabilities, Noncurrent | (2,121)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryLiabilityAxis = us-gaap_OtherRegulatoryAssetsLiabilitiesMember | (3,361)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryLiabilityAxis = us-gaap_OtherRegulatoryAssetsLiabilitiesMember
Advanced Metering Infrastructure Costs [Member] | Texas-New Mexico Power Company [Member] |  |
Regulatory Liabilities |  |
Regulatory liabilities, Noncurrent | (5,227)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryLiabilityAxis = us-gaap_AdvancedMeteringInfrastructureCostsMember | (7,251)us-gaap_RegulatoryLiabilityNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryLiabilityAxis = us-gaap_AdvancedMeteringInfrastructureCostsMember
Regulatory Assets, Transmission Cost Recovery [Member] | Texas-New Mexico Power Company [Member] |  |
Regulatory Assets |  |
Regulatory Assets, Current | 2,482us-gaap_RegulatoryAssetsCurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryAssetAxis = pnm_RegulatoryAssetsTransmissionCostRecoveryMember | 4,250us-gaap_RegulatoryAssetsCurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryAssetAxis = pnm_RegulatoryAssetsTransmissionCostRecoveryMember
Other Regulatory Assets (Liabilities) [Member] | Public Service Company of New Mexico [Member] |  |
Regulatory Assets |  |
Regulatory Assets, Noncurrent | 5,929us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryAssetAxis = us-gaap_OtherRegulatoryAssetsLiabilitiesMember | 9,345us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryAssetAxis = us-gaap_OtherRegulatoryAssetsLiabilitiesMember
Other Regulatory Assets (Liabilities) [Member] | Texas-New Mexico Power Company [Member] |  |
Regulatory Assets |  |
Regulatory Assets, Current | 1,393us-gaap_RegulatoryAssetsCurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryAssetAxis = us-gaap_OtherRegulatoryAssetsLiabilitiesMember | 772us-gaap_RegulatoryAssetsCurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryAssetAxis = us-gaap_OtherRegulatoryAssetsLiabilitiesMember
Regulatory Assets, Noncurrent | 1,155us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryAssetAxis = us-gaap_OtherRegulatoryAssetsLiabilitiesMember | 1,627us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryAssetAxis = us-gaap_OtherRegulatoryAssetsLiabilitiesMember
Stranded costs [Member] | Texas-New Mexico Power Company [Member] |  |
Regulatory Assets |  |
Regulatory Assets, Noncurrent | 55,292us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryAssetAxis = us-gaap_StrandedCostsMember | 63,606us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryAssetAxis = us-gaap_StrandedCostsMember
Environmental Restoration Costs [Member] | Public Service Company of New Mexico [Member] |  |
Regulatory Assets |  |
Regulatory Assets, Noncurrent | 34,224us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryAssetAxis = us-gaap_EnvironmentalRestorationCostsMember | 40,144us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryAssetAxis = us-gaap_EnvironmentalRestorationCostsMember
Deferred Income Tax Charge [Member] | Public Service Company of New Mexico [Member] |  |
Regulatory Assets |  |
Regulatory Assets, Noncurrent | 63,645us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryAssetAxis = us-gaap_DeferredIncomeTaxChargesMember | 61,850us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryAssetAxis = us-gaap_DeferredIncomeTaxChargesMember
Deferred Income Tax Charge [Member] | Texas-New Mexico Power Company [Member] |  |
Regulatory Assets |  |
Regulatory Assets, Noncurrent | 10,556us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryAssetAxis = us-gaap_DeferredIncomeTaxChargesMember | 10,868us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryAssetAxis = us-gaap_DeferredIncomeTaxChargesMember
Loss on reacquired debt [Member] | Public Service Company of New Mexico [Member] |  |
Regulatory Assets |  |
Regulatory Assets, Noncurrent | 25,439us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryAssetAxis = us-gaap_LossOnReacquiredDebtMember | 27,490us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryAssetAxis = us-gaap_LossOnReacquiredDebtMember
Loss on reacquired debt [Member] | Texas-New Mexico Power Company [Member] |  |
Regulatory Assets |  |
Regulatory Assets, Noncurrent | 36,703us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryAssetAxis = us-gaap_LossOnReacquiredDebtMember | 38,616us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryAssetAxis = us-gaap_LossOnReacquiredDebtMember
Pension and Other Postretirement Plans Costs [Member] | Public Service Company of New Mexico [Member] |  |
Regulatory Assets |  |
Regulatory Assets, Noncurrent | 222,545us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryAssetAxis = us-gaap_PensionAndOtherPostretirementPlansCostsMember | 206,691us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryAssetAxis = us-gaap_PensionAndOtherPostretirementPlansCostsMember
Pension and Other Postretirement Plans Costs [Member] | Texas-New Mexico Power Company [Member] |  |
Regulatory Assets |  |
Regulatory Assets, Noncurrent | 23,803us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryAssetAxis = us-gaap_PensionAndOtherPostretirementPlansCostsMember | 19,938us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryAssetAxis = us-gaap_PensionAndOtherPostretirementPlansCostsMember
Fuel and purchased power adjustment clause [Member] | Public Service Company of New Mexico [Member] |  |
Regulatory Assets |  |
Regulatory Assets, Noncurrent | 0us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryAssetAxis = pnm_FuelAndPurchasedPowerAdjustmentClauseMember | 25,386us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryAssetAxis = pnm_FuelAndPurchasedPowerAdjustmentClauseMember
Renewable Energy Program [Member] | Public Service Company of New Mexico [Member] |  |
Regulatory Assets |  |
Regulatory Assets, Noncurrent | 5,263us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryAssetAxis = us-gaap_RenewableEnergyProgramMember | 13,311us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RegulatoryAssetAxis = us-gaap_RenewableEnergyProgramMember
Advanced Metering Infrastructure Costs [Member] | Texas-New Mexico Power Company [Member] |  |
Regulatory Assets |  |
Regulatory Assets, Noncurrent | $ 6,453us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryAssetAxis = us-gaap_AdvancedMeteringInfrastructureCostsMember | $ 5,083us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RegulatoryAssetAxis = us-gaap_AdvancedMeteringInfrastructureCostsMember

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- Definition The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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- Definition Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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- Definition The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 405 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394 + Details
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- Definition The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 405 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394 + Details
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