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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
	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	$ 5.3us-gaap_PublicUtilitiesApprovedRateIncreaseDecreaseAmount / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_ScheduleOfRegulatoryRateMattersAxis = pnm_FirmRequirementsWholesalePowerRateCaseNavopacheMemberMember
Public Utilities, Average monthly usage in megawatts		55pnm_PublicUtilitiesAveragemonthlyusageinmegawatts / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_ScheduleOfRegulatoryRateMattersAxis = pnm_FirmRequirementsWholesalePowerRateCaseNavopacheMemberMember
Public Utilities, Revenue For Power Sold Under Specific Contract		28.4pnm_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	$ 6.1pnm_PublicUtilitiesRevenueForPowerSoldUnderSpecificContract / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_ScheduleOfRegulatoryRateMattersAxis = pnm_CityOfGallupNewMexicoContractMember

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- Definition

Public Utilities, Average monthly usage in megawatts

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Public Utilities, Contract Extension

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Public Utilities, Revenue For Power Sold Under Specific Contract

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- Definition

Amount of public utility's approved rate increase (decrease) by regulatory agency.

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