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Regulatory and Rate Matters - Integrated Resource Plan and Four Corners Right of First Refusal (Details) (Public Service Company of New Mexico [Member]) | 1 Months Ended | 3 Months Ended | 4 Months Ended |
--- | --- | --- | --- | ---
Jul. 31, 2011 | Mar. 31, 2015 | Jun. 17, 2015 | Feb. 17, 2015
Integrated Resource Plan, 2011 [Member] |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Public Utilities, Frequency of IRP filings |  | 3 years |  |
Public Utilities, Planning Period Covered of IRP | 20 years |  |  |
Four Corners [Member] |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Jointly Owned Utility Plant Proportionate Ownership Share, Other Entities |  |  |  | 7.00%pnm_JointlyOwnedUtilityPlantProportionateOwnershipShareOtherEntities / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_FourCornersMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Subsequent Event [Member] | Four Corners [Member] |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Period of time to file a waiver of rights of first refusal |  |  | 120 days |

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