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Regulatory and Rate Matters - Proceeding Regarding Definition of Future Test Year (Details) | Dec. 07, 2016
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2014 Electric Rate Case | Public Service Company of New Mexico |
Public Utilities, General Disclosures [Line Items] |
Redefined future test year as period that begins a period of time following the filing of a rate case application (up to) | 13 months

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- Definition Future test year period, Revised, Number of days following the filing of application for rate increase + References No definition available. + Details
Name: | pnm_FuturetestyearperiodRevisedNumberofdaysfollowingthefilingofapplicationforrateincrease
Namespace Prefix: | pnm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesGeneralDisclosuresLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | pnm_ScheduleOfRegulatoryRateMattersAxis=pnm_A2014ElectricRateCaseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | dei_LegalEntityAxis=pnm_PublicServiceCompanyOfNewMexicoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |