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Construction Program and Jointly-Owned Electric Generating Plants Construction Program and Jointly-Owned Electric Generating Plants (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012
Construction Expenditures	$ 460,658us-gaap_PaymentsToAcquireProductiveAssets		$ 348,039us-gaap_PaymentsToAcquireProductiveAssets	$ 308,909us-gaap_PaymentsToAcquireProductiveAssets
Public Utilities, Property, Plant and Equipment, Plant in Service	5,941,581us-gaap_PublicUtilitiesPropertyPlantAndEquipmentPlantInService		5,563,061us-gaap_PublicUtilitiesPropertyPlantAndEquipmentPlantInService
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	(1,939,760)us-gaap_PublicUtilitiesPropertyPlantAndEquipmentAccumulatedDepreciation		(1,838,832)us-gaap_PublicUtilitiesPropertyPlantAndEquipmentAccumulatedDepreciation
Operating Lease, Extended Term	2 years
Joint Projects [Member] | Public Service Company of New Mexico [Member]
Construction Expenditures	316,800us-gaap_PaymentsToAcquireProductiveAssets / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_JointProjectsMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Joint Projects [Member] | Texas-New Mexico Power Company [Member]
Construction Expenditures	127,200us-gaap_PaymentsToAcquireProductiveAssets / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_JointProjectsMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Joint Projects [Member] | PNMR [Member]
Construction Expenditures	460,700us-gaap_PaymentsToAcquireProductiveAssets / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_JointProjectsMember / dei_LegalEntityAxis = pnm_PnmrMember
Four Corners Units 4 and 5 (Coal) [Member] | Public Service Company of New Mexico [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service	162,111us-gaap_PublicUtilitiesPropertyPlantAndEquipmentPlantInService / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_FourCornersUnits4And5CoalMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	(101,007)us-gaap_PublicUtilitiesPropertyPlantAndEquipmentAccumulatedDepreciation / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_FourCornersUnits4And5CoalMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	8,253us-gaap_PublicUtilitiesPropertyPlantAndEquipmentConstructionWorkInProgress / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_FourCornersUnits4And5CoalMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Jointly Owned Utility Plant, Proportionate Ownership Share	13.00%us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_FourCornersUnits4And5CoalMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Luna (Gas) [Member] | Other Unrelated Entities 9 [Member]
Jointly Owned Utility Plant, Proportionate Ownership Share	33.30%us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_LunaGasMember / pnm_OtherEntitiesAxis = pnm_OtherUnrelatedEntities9Member
Luna (Gas) [Member] | Public Service Company of New Mexico [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service	66,169us-gaap_PublicUtilitiesPropertyPlantAndEquipmentPlantInService / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_LunaGasMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	(20,297)us-gaap_PublicUtilitiesPropertyPlantAndEquipmentAccumulatedDepreciation / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_LunaGasMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	136us-gaap_PublicUtilitiesPropertyPlantAndEquipmentConstructionWorkInProgress / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_LunaGasMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Jointly Owned Utility Plant, Proportionate Ownership Share	33.33%us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_LunaGasMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
SJGS Units 1 and 2 [Member] | Public Service Company of New Mexico [Member]
Jointly Owned Utility Plant, Proportionate Ownership Share	50.00%us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SjgsUnits1And2Member / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
SJGS (Coal) [Member] | Unit 3 [Member] | Other Unrelated Entities 1 [Member]
Jointly Owned Utility Plant Proportionate Ownership Share, Other Entities	41.80%pnm_JointlyOwnedUtilityPlantProportionateOwnershipShareOtherEntities / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SjgsCoalMember / pnm_OtherEntitiesAxis = pnm_OtherUnrelatedEntities1Member / pnm_UnitAxis = pnm_Unit3Member
SJGS (Coal) [Member] | Unit 3 [Member] | Other Unrelated Entities 2 [Member]
Jointly Owned Utility Plant, Proportionate Ownership Share	8.20%us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SjgsCoalMember / pnm_OtherEntitiesAxis = pnm_OtherUnrelatedEntities2Member / pnm_UnitAxis = pnm_Unit3Member
SJGS (Coal) [Member] | Unit 4 [Member] | Other Unrelated Entities 3 [Member]
Jointly Owned Utility Plant Proportionate Ownership Share, Other Entities	28.80%pnm_JointlyOwnedUtilityPlantProportionateOwnershipShareOtherEntities / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SjgsCoalMember / pnm_OtherEntitiesAxis = pnm_OtherUnrelatedEntities3Member / pnm_UnitAxis = pnm_Unit4Member
SJGS (Coal) [Member] | Unit 4 [Member] | Other Unrelated Entities 4 [Member]
Jointly Owned Utility Plant Proportionate Ownership Share, Other Entities	10.04%pnm_JointlyOwnedUtilityPlantProportionateOwnershipShareOtherEntities / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SjgsCoalMember / pnm_OtherEntitiesAxis = pnm_OtherUnrelatedEntities4Member / pnm_UnitAxis = pnm_Unit4Member
SJGS (Coal) [Member] | Unit 4 [Member] | Other Unrelated Entities 5 [Member]
Jointly Owned Utility Plant Proportionate Ownership Share, Other Entities	8.475%pnm_JointlyOwnedUtilityPlantProportionateOwnershipShareOtherEntities / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SjgsCoalMember / pnm_OtherEntitiesAxis = pnm_OtherUnrelatedEntities5Member / pnm_UnitAxis = pnm_Unit4Member
SJGS (Coal) [Member] | Unit 4 [Member] | Other Unrelated Entities 6 [Member]
Jointly Owned Utility Plant Proportionate Ownership Share, Other Entities	7.20%pnm_JointlyOwnedUtilityPlantProportionateOwnershipShareOtherEntities / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SjgsCoalMember / pnm_OtherEntitiesAxis = pnm_OtherUnrelatedEntities6Member / pnm_UnitAxis = pnm_Unit4Member
SJGS (Coal) [Member] | Unit 4 [Member] | Other Unrelated Entities 7 [Member]
Jointly Owned Utility Plant Proportionate Ownership Share, Other Entities	7.028%pnm_JointlyOwnedUtilityPlantProportionateOwnershipShareOtherEntities / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SjgsCoalMember / pnm_OtherEntitiesAxis = pnm_OtherUnrelatedEntities7Member / pnm_UnitAxis = pnm_Unit4Member
SJGS (Coal) [Member] | Public Service Company of New Mexico [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service	1,009,378us-gaap_PublicUtilitiesPropertyPlantAndEquipmentPlantInService / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SjgsCoalMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	(423,364)us-gaap_PublicUtilitiesPropertyPlantAndEquipmentAccumulatedDepreciation / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SjgsCoalMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	25,551us-gaap_PublicUtilitiesPropertyPlantAndEquipmentConstructionWorkInProgress / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SjgsCoalMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Jointly Owned Utility Plant, Proportionate Ownership Share	46.30%us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SjgsCoalMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
SJGS (Coal) [Member] | Public Service Company of New Mexico [Member] | Unit 3 [Member]
Jointly Owned Utility Plant, Proportionate Ownership Share	50.00%us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SjgsCoalMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_UnitAxis = pnm_Unit3Member
SJGS (Coal) [Member] | Public Service Company of New Mexico [Member] | Unit 4 [Member]
Jointly Owned Utility Plant, Proportionate Ownership Share	38.457%us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_SjgsCoalMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / pnm_UnitAxis = pnm_Unit4Member
Palo Verde Nuclear Generating Station [Member] | Public Service Company of New Mexico [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service	533,702us-gaap_PublicUtilitiesPropertyPlantAndEquipmentPlantInService / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember	[1]
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	(152,273)us-gaap_PublicUtilitiesPropertyPlantAndEquipmentAccumulatedDepreciation / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember	[1]
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	$ 42,334us-gaap_PublicUtilitiesPropertyPlantAndEquipmentConstructionWorkInProgress / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember	[1]
Jointly Owned Utility Plant, Proportionate Ownership Share	10.20%us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember	[1]
Operating Lease, Original term	40 years
Number of operating units	3pnm_NumberOfOperatingUnits / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Operating Lease, Extended Term	20 years
[1] Includes interest in PVNGS Unit 3, interest in common facilities for all PVNGS units, and owned interests in PVNGS Units 1 and 2.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 360

-Section S99

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Investing Activities

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-Name Accounting Standards Codification

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