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v3.20.2

Subsequent Event (Details) - Forecast $ / shares in Units, $ in Millions | 3 Months Ended
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Dec. 31, 2021 USD ($) $ / shares
Merger Agreement |
Subsequent Event [Line Items] |
Business combination, cash right per common share (in dollars per share) | $ / shares | $ 50.30
Out-of-pocket fees and expenses reimbursement | $ 10.0
PNMR | Merger Agreement |
Subsequent Event [Line Items] |
Termination fees | 130.0
Avangrid | Merger Agreement |
Subsequent Event [Line Items] |
Termination fees | $ 184.0
Avangrid | Iberdrola, S.A. |
Subsequent Event [Line Items] |
Noncontrolling interest, ownership percentage by parent | 81.50%

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- Definition Business Combination, Cash Right Per Common Share + References No definition available. + Details
Name: | pnm_BusinessCombinationCashRightPerCommonShare
Namespace Prefix: | pnm_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

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- Definition Out-of-pocket Fees And Expenses Reimbursement + References No definition available. + Details
Name: | pnm_OutOfPocketFeesAndExpensesReimbursement
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Termination Fees + References No definition available. + Details
Name: | pnm_TerminationFees
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition The parent entity's interest in net assets of the subsidiary, expressed as a percentage. + References No definition available. + Details
Name: | us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_BusinessAcquisitionAxis=pnm_MergerAgreementMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_StatementScenarioAxis=srt_ScenarioForecastMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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

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- Details
Name: | srt_OwnershipAxis=pnm_AvangridMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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