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Asset Retirement Obligations (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Liability Beginning Balance	$ 96,135,000us-gaap_AssetRetirementObligation		$ 85,893,000us-gaap_AssetRetirementObligation		$ 79,233,000us-gaap_AssetRetirementObligation
Liabilities incurred	0us-gaap_AssetRetirementObligationLiabilitiesIncurred		0us-gaap_AssetRetirementObligationLiabilitiesIncurred		0us-gaap_AssetRetirementObligationLiabilitiesIncurred
Liabilities settled	0us-gaap_AssetRetirementObligationLiabilitiesSettled		(79,000)us-gaap_AssetRetirementObligationLiabilitiesSettled		(25,000)us-gaap_AssetRetirementObligationLiabilitiesSettled
Accretion expense	7,984,000us-gaap_AssetRetirementObligationAccretionExpense		7,245,000us-gaap_AssetRetirementObligationAccretionExpense		6,685,000us-gaap_AssetRetirementObligationAccretionExpense
Revisions to estimated cash flows	51,000us-gaap_AssetRetirementObligationRevisionOfEstimate	[1]	3,076,000us-gaap_AssetRetirementObligationRevisionOfEstimate	[1]
Liability Ending Balance	104,170,000us-gaap_AssetRetirementObligation		96,135,000us-gaap_AssetRetirementObligation		85,893,000us-gaap_AssetRetirementObligation
Public Service Company of New Mexico [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Liability Beginning Balance	95,225,000us-gaap_AssetRetirementObligation / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember		85,042,000us-gaap_AssetRetirementObligation / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember		78,425,000us-gaap_AssetRetirementObligation / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Liabilities incurred	0us-gaap_AssetRetirementObligationLiabilitiesIncurred / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember		0us-gaap_AssetRetirementObligationLiabilitiesIncurred / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember		0us-gaap_AssetRetirementObligationLiabilitiesIncurred / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Liabilities settled	0us-gaap_AssetRetirementObligationLiabilitiesSettled / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember		(67,000)us-gaap_AssetRetirementObligationLiabilitiesSettled / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember		0us-gaap_AssetRetirementObligationLiabilitiesSettled / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Accretion expense	7,906,000us-gaap_AssetRetirementObligationAccretionExpense / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember		7,174,000us-gaap_AssetRetirementObligationAccretionExpense / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember		6,617,000us-gaap_AssetRetirementObligationAccretionExpense / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Revisions to estimated cash flows	51,000us-gaap_AssetRetirementObligationRevisionOfEstimate / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember	[1]	3,076,000us-gaap_AssetRetirementObligationRevisionOfEstimate / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember	[1]
Liability Ending Balance	103,182,000us-gaap_AssetRetirementObligation / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember		95,225,000us-gaap_AssetRetirementObligation / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember		85,042,000us-gaap_AssetRetirementObligation / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)	500,000us-gaap_AssetRetirementObligationPeriodIncreaseDecrease / us-gaap_BusinessAcquisitionAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Public Service Company of New Mexico [Member] | San Juan Generating Station [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)	2,500,000us-gaap_AssetRetirementObligationPeriodIncreaseDecrease / us-gaap_BusinessAcquisitionAxis = pnm_SanJuanGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Texas-New Mexico Power Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Liability Beginning Balance	782,000us-gaap_AssetRetirementObligation / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember		732,000us-gaap_AssetRetirementObligation / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember		699,000us-gaap_AssetRetirementObligation / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Liabilities incurred	0us-gaap_AssetRetirementObligationLiabilitiesIncurred / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember		0us-gaap_AssetRetirementObligationLiabilitiesIncurred / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember		0us-gaap_AssetRetirementObligationLiabilitiesIncurred / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Liabilities settled	0us-gaap_AssetRetirementObligationLiabilitiesSettled / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember		(12,000)us-gaap_AssetRetirementObligationLiabilitiesSettled / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember		(25,000)us-gaap_AssetRetirementObligationLiabilitiesSettled / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Accretion expense	66,000us-gaap_AssetRetirementObligationAccretionExpense / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember		62,000us-gaap_AssetRetirementObligationAccretionExpense / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember		58,000us-gaap_AssetRetirementObligationAccretionExpense / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Revisions to estimated cash flows	0us-gaap_AssetRetirementObligationRevisionOfEstimate / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember	[1]	0us-gaap_AssetRetirementObligationRevisionOfEstimate / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember	[1]
Liability Ending Balance	$ 848,000us-gaap_AssetRetirementObligation / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember		$ 782,000us-gaap_AssetRetirementObligation / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember		$ 732,000us-gaap_AssetRetirementObligation / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
[1] Based on studies to estimate the amount and timing of future ARO expenditures. PNM has an ARO for PVNGS that includes the obligations for nuclear decommissioning of that facility. In 2013, a new decommissioning study for PVNGS was implemented reflecting updated cash flow estimates, including the extended operating licenses. The new study resulted in an increase of $0.5 million to the ARO. In addition, a new decommissioning study for SJGS was implemented in 2013, resulting in a $2.5 million increase to the ARO.

X

- Definition

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849



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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Asset Retirement Obligation

-URI http://asc.fasb.org/extlink&oid=6505190

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X

- Definition

Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)(3)

-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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- Definition

Amount of asset retirement obligations incurred during the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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- Definition

Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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- Definition

Net Increase or Decrease in the asset retirement obligation during the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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Amount of the Increase or Decrease in the amount of the asset retirement obligation during the current period for changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)(4)

-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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