Asset Retirement Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Asset Retirement Obligations [Line Items]
ARO liabilities related to nuclear decommissioning	76.00%
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	$ 181,962	$ 158,674	$ 146,679
Liabilities incurred	0	0	0
Liabilities settled	(1,444)	(987)	(192)
Accretion expense	11,310	12,635	11,482
Revisions to estimated cash flows	(8,407)	11,640	705
Ending balance	183,421	181,962	158,674
Four Corners
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Revisions to estimated cash flows	800
Palo Verde Nuclear Generating Station
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Revisions to estimated cash flows	9,200
Public Service Company of New Mexico
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	181,081	157,814	145,707
Liabilities incurred	0	0	0
Liabilities settled	(1,192)	(935)	0
Accretion expense	11,235	12,562	11,402
Revisions to estimated cash flows	(8,407)	11,640	705
Ending balance	182,717	181,081	157,814
Texas-New Mexico Power Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	881	860	793
Liabilities incurred	0	0	0
Liabilities settled	(252)	(52)	0
Accretion expense	75	73	67
Revisions to estimated cash flows	0	0	0
Ending balance	$ 704	$ 881	$ 860

Asset Retirement Obligation, Liabilities Related to Nuclear Decommissioning

No definition available.

Name:	pnm_AssetRetirementObligationLiabilitiesRelatedtoNuclearDecommissioning
Namespace Prefix:	pnm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Asset Retirement Obligations [Line Items]

+ References

No definition available.

+ Details

Name:	pnm_AssetRetirementObligationsLineItems
Namespace Prefix:	pnm_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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

+ Details

Name:	us-gaap_AssetRetirementObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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://fasb.org/us-gaap/role/ref/legacyRef
-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

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-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

+ Details

Name:	us-gaap_AssetRetirementObligationAccretionExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of asset retirement obligations incurred during the period.

+ References

+ Details

Name:	us-gaap_AssetRetirementObligationLiabilitiesIncurred
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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

+ Details

Name:	us-gaap_AssetRetirementObligationLiabilitiesSettled
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 35
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6392603&loc=d3e7123-110846

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-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

+ Details

Name:	us-gaap_AssetRetirementObligationRevisionOfEstimate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

Name:	us-gaap_AssetRetirementObligationRollForwardAnalysisRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=pnm_FourCornersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=pnm_PaloVerdeNuclearGeneratingStationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=pnm_PublicServiceCompanyOfNewMexicoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=pnm_TexasNewMexicoPowerCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: