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Regulatory and Rate Matters - Energy Efficiency (Details) - Texas-New Mexico Power Company $ in Millions | Aug. 30, 2019 USD ($)
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Public Utilities, General Disclosures [Line Items] |
Energy efficiency cost recovery factor, requested change amount | $ 5.9
Energy efficiency cost recovery factor, requested performance bonus | $ 0.8

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- Definition Energy Efficiency Cost Recovery Factor, Requested Change Amount + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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- Definition Energy Efficiency Cost Recovery Factor, Requested Performance Bonus + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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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: | dei_LegalEntityAxis=pnm_TexasNewMexicoPowerCompanyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |