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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