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Goodwill; Impairments (Details) (USD $) | 12 Months Ended |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Dec. 31, 2008 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Apr. 01, 2014 | Apr. 01, 2013 | Apr. 01, 2012
Schedule of Goodwill and Other Intangible Assets [Line Items] |  |  |  |  |  |  |
Goodwill |  | $ 278,297,000us-gaap_Goodwill | $ 278,297,000us-gaap_Goodwill | $ 278,297,000us-gaap_Goodwill |  |  |
Goodwill, Impairment Loss | 174,400,000us-gaap_GoodwillImpairmentLoss |  |  |  |  |  |
Public Service Company of New Mexico [Member] |  |  |  |  |  |  |
Schedule of Goodwill and Other Intangible Assets [Line Items] |  |  |  |  |  |  |
Goodwill |  | 51,600,000us-gaap_Goodwill / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 51,600,000us-gaap_Goodwill / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount |  |  |  |  | 30.00%us-gaap_ReportingUnitPercentageOfFairValueInExcessOfCarryingAmount / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 27.00%us-gaap_ReportingUnitPercentageOfFairValueInExcessOfCarryingAmount / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |
Goodwill, Reporting Unit, Sensitivity analysis, Percentage Increase in Expected Return on Equity |  |  |  |  | 0.50%pnm_GoodwillReportingUnitSensitivityanalysisPercentageIncreaseinExpectedReturnonEquity / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |
Goodwill, Reporting Unit, Sensitivity analysis, Reduced Percentage of Fair Value in Excess of Carrying Value |  |  |  |  | 23.00%pnm_GoodwillReportingUnitSensitivityanalysisReducedPercentageofFairValueinExcessofCarryingValue / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember | 20.00%pnm_GoodwillReportingUnitSensitivityanalysisReducedPercentageofFairValueinExcessofCarryingValue / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |
Goodwill, Impairment Loss | 51,100,000us-gaap_GoodwillImpairmentLoss / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  |  |  |  |  |
Texas-New Mexico Power Company [Member] |  |  |  |  |  |  |
Schedule of Goodwill and Other Intangible Assets [Line Items] |  |  |  |  |  |  |
Goodwill |  | 226,700,000us-gaap_Goodwill / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember | 226,700,000us-gaap_Goodwill / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember |  |  |  |
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount |  |  |  |  |  |  | 26.00%us-gaap_ReportingUnitPercentageOfFairValueInExcessOfCarryingAmount / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Goodwill, Impairment Loss | $ 34,500,000us-gaap_GoodwillImpairmentLoss / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember |  |  |  |  |  |

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