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Regulatory and Rate Matters - Firm-Requirements Wholesale Customers (Details) (Public Service Company of New Mexico [Member], USD $) In Millions, unless otherwise specified | 3 Months Ended | 12 Months Ended
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Mar. 31, 2015 | Dec. 31, 2014 MW
Firm Requirements Wholesale Power Rate Case, Navopache [Member] [Member] |  |
Public Utilities, General Disclosures [Line Items] |  |
Public Utilities, Approved Rate Increase (Decrease), Amount | $ 5.3 us-gaap_PublicUtilitiesApprovedRateIncreaseDecreaseAmount / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_ScheduleOfRegulatoryRateMattersAxis = pnm_FirmRequirementsWholesalePowerRateCaseNavopacheMemberMember |
Public Utilities, Average monthly usage in megawatts |  | 55 pnm_PublicUtilitiesAveragemonthlyusageinmegawatts / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_ScheduleOfRegulatoryRateMattersAxis = pnm_FirmRequirementsWholesalePowerRateCaseNavopacheMemberMember
Public Utilities, Revenue For Power Sold Under Specific Contract |  | 28.4 pnm_PublicUtilitiesRevenueForPowerSoldUnderSpecificContract / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_ScheduleOfRegulatoryRateMattersAxis = pnm_FirmRequirementsWholesalePowerRateCaseNavopacheMemberMember
Firm Requirements Wholesale Power Rate Case [Member] |  |
Public Utilities, General Disclosures [Line Items] |  |
Public Utilities, Contract Extension | 10 years |
City of Gallup, New Mexico Contract [Member] |  |
Public Utilities, General Disclosures [Line Items] |  |
Public Utilities, Revenue For Power Sold Under Specific Contract | $ 6.1 pnm_PublicUtilitiesRevenueForPowerSoldUnderSpecificContract / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_ScheduleOfRegulatoryRateMattersAxis = pnm_CityOfGallupNewMexicoContractMember |

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- Definition Public Utilities, Average monthly usage in megawatts + References No definition available. + Details
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- Definition Public Utilities, Contract Extension + References No definition available. + Details
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- Definition Public Utilities, Revenue For Power Sold Under Specific Contract + References No definition available. + Details
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- Definition Amount of public utility's approved rate increase (decrease) by regulatory agency. + References No definition available. + Details
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- Details
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- Details
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- Details
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- Details
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