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Regulatory and Rate Matters - Formula Transmission Rate Case (Details) (Formula Transmission Rate Case [Member], Public Service Company of New Mexico [Member], USD $) In Millions, unless otherwise specified | 0 Months Ended | 3 Months Ended |
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May 02, 2014 | Jun. 03, 2013 | Mar. 31, 2015 | Mar. 20, 2015 party
Formula Transmission Rate Case [Member] | Public Service Company of New Mexico [Member] |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Amount of Regulatory Costs Not yet Approved |  |  | $ 3.2 us-gaap_AmountOfRegulatoryCostsNotYetApproved / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_ScheduleOfRegulatoryRateMattersAxis = pnm_FormulaTransmissionRateCaseMember |
Public Utilities, Return on Equity |  |  | 10.81%pnm_PublicUtilitiesReturnonEquity / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_ScheduleOfRegulatoryRateMattersAxis = pnm_FormulaTransmissionRateCaseMember | 10.00%pnm_PublicUtilitiesReturnonEquity / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_ScheduleOfRegulatoryRateMattersAxis = pnm_FormulaTransmissionRateCaseMember
Percentage ownership of EIP transmission line |  |  | 60.00%pnm_PercentageOwnershipOfEipTransmissionLine / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_ScheduleOfRegulatoryRateMattersAxis = pnm_FormulaTransmissionRateCaseMember |
Public Utilities, Requested Rate Increase (Decrease), Amount | 0.5 us-gaap_PublicUtilitiesRequestedRateIncreaseDecreaseAmount / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_ScheduleOfRegulatoryRateMattersAxis = pnm_FormulaTransmissionRateCaseMember | 1.3 us-gaap_PublicUtilitiesRequestedRateIncreaseDecreaseAmount / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_ScheduleOfRegulatoryRateMattersAxis = pnm_FormulaTransmissionRateCaseMember |  |
Number of other parties to settlement |  |  |  | 5 pnm_Numberofotherpartiestosettlement / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_ScheduleOfRegulatoryRateMattersAxis = pnm_FormulaTransmissionRateCaseMember
Public Utilities, Approved Rate Increase (Decrease), Amount |  |  | $ 1.3 us-gaap_PublicUtilitiesApprovedRateIncreaseDecreaseAmount / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_ScheduleOfRegulatoryRateMattersAxis = pnm_FormulaTransmissionRateCaseMember |

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- Definition Percentage ownership of EIP transmission line + References No definition available. + Details
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- Definition Amount of regulatory costs not yet approved by the regulatory authority. + 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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- Definition Amount of public utility's requested rate increase (decrease) with regulatory agency. + References No definition available. + Details
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