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Income Taxes Interest Expense (Income) Related to Income Taxes (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Income Taxes [Line Items] |  |  |
Interest income related to income taxes | $ 146us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense | $ 242us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense | $ 243us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense
Public Service Company of New Mexico [Member] |  |  |
Income Taxes [Line Items] |  |  |
Interest income related to income taxes | 148us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 251us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 244us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Texas-New Mexico Power Company [Member] |  |  |
Income Taxes [Line Items] |  |  |
Interest income related to income taxes | $ (2)us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | $ (2)us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | $ (3)us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember

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- Definition Amount of interest expense for an underpayment of income taxes. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319 + Details
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