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Summary of the Business and Significant Accounting Policies (Inventories/Depreciation and Amortization) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Public Utilities, Inventory [Line Items]
Inventory, Net	63,628us-gaap_InventoryNet	67,223us-gaap_InventoryNet
Coal [Member]
Public Utilities, Inventory [Line Items]
Inventory, Net	17,525us-gaap_InventoryNet / us-gaap_PublicUtilitiesInventoryAxis = us-gaap_PublicUtilitiesInventoryCoalMember	24,872us-gaap_InventoryNet / us-gaap_PublicUtilitiesInventoryAxis = us-gaap_PublicUtilitiesInventoryCoalMember
Materials and supplies [Member]
Public Utilities, Inventory [Line Items]
Inventory, Net	46,103us-gaap_InventoryNet / us-gaap_PublicUtilitiesInventoryAxis = pnm_PublicUtilitiesInventoryMaterialsAndSuppliesMember	42,351us-gaap_InventoryNet / us-gaap_PublicUtilitiesInventoryAxis = pnm_PublicUtilitiesInventoryMaterialsAndSuppliesMember
Public Service Company of New Mexico [Member]
Public Utilities, Inventory [Line Items]
Inventory, Net	60,859us-gaap_InventoryNet / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember	64,520us-gaap_InventoryNet / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Public Service Company of New Mexico [Member] | Coal [Member]
Public Utilities, Inventory [Line Items]
Inventory, Net	17,525us-gaap_InventoryNet / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PublicUtilitiesInventoryAxis = us-gaap_PublicUtilitiesInventoryCoalMember	24,872us-gaap_InventoryNet / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PublicUtilitiesInventoryAxis = us-gaap_PublicUtilitiesInventoryCoalMember
Public Service Company of New Mexico [Member] | Materials and supplies [Member]
Public Utilities, Inventory [Line Items]
Inventory, Net	43,334us-gaap_InventoryNet / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PublicUtilitiesInventoryAxis = pnm_PublicUtilitiesInventoryMaterialsAndSuppliesMember	39,648us-gaap_InventoryNet / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PublicUtilitiesInventoryAxis = pnm_PublicUtilitiesInventoryMaterialsAndSuppliesMember
Public Service Company of New Mexico [Member] | Electric plant [Member]
Public Utilities, Inventory [Line Items]
Depreciation average rates used (as a percent)	2.26%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PublicUtilityAxis = us-gaap_ElectricityGenerationPlantNonNuclearMember	2.27%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PublicUtilityAxis = us-gaap_ElectricityGenerationPlantNonNuclearMember	2.25%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PublicUtilityAxis = us-gaap_ElectricityGenerationPlantNonNuclearMember
Public Service Company of New Mexico [Member] | Common, intangible, and general plant [Member]
Public Utilities, Inventory [Line Items]
Depreciation average rates used (as a percent)	4.64%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PublicUtilityAxis = pnm_CommonIntangibleAndGeneralPlantMember	4.87%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PublicUtilityAxis = pnm_CommonIntangibleAndGeneralPlantMember	5.35%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_PublicUtilityAxis = pnm_CommonIntangibleAndGeneralPlantMember
Texas-New Mexico Power Company [Member]
Public Utilities, Inventory [Line Items]
Inventory, Net	2,769us-gaap_InventoryNet / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember	2,703us-gaap_InventoryNet / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Depreciation average rates used (as a percent)	3.59%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember	3.66%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember	3.56%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Texas-New Mexico Power Company [Member] | Coal [Member]
Public Utilities, Inventory [Line Items]
Inventory, Net	0us-gaap_InventoryNet / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_PublicUtilitiesInventoryAxis = us-gaap_PublicUtilitiesInventoryCoalMember	0us-gaap_InventoryNet / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_PublicUtilitiesInventoryAxis = us-gaap_PublicUtilitiesInventoryCoalMember
Texas-New Mexico Power Company [Member] | Materials and supplies [Member]
Public Utilities, Inventory [Line Items]
Inventory, Net	2,769us-gaap_InventoryNet / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_PublicUtilitiesInventoryAxis = pnm_PublicUtilitiesInventoryMaterialsAndSuppliesMember	2,703us-gaap_InventoryNet / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_PublicUtilitiesInventoryAxis = pnm_PublicUtilitiesInventoryMaterialsAndSuppliesMember

X

- Definition

Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.6(a))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 330

-SubTopic 10

-Section 35

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6386567&loc=d3e3927-108312



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section 45

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28358313&loc=d3e6676-107765

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X

- Definition

Composite depreciation rate for public utility plants in service.

+ References

No definition available.

+ Details

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- Details

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- Details

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