Available-for-sale Securities, Accumulated Gross Unrealized Gain, Net of Tax, Total

No definition available.

Name:	pnm_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedGainNetofTaxTotal
Namespace Prefix:	pnm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Collaborative Arrangement, Owner Obligations, Default, Amount

+ References

No definition available.

+ Details

Name:	pnm_CollaborativeArrangementOwnerObligationsDefaultAmount
Namespace Prefix:	pnm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

Aggregate dividends declared during the period for each share of common stock outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

+ Details

Name:	us-gaap_CommonStockDividendsPerShareDeclared
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of paid and unpaid common stock dividends declared with the form of settlement in cash.

+ References

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

The distributions of earnings to an entity that is affiliated with the reporting entity by means of direct or indirect ownership.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585

+ Details

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

- 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:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Significant Accounting Policies and Responsibility for Financial Statements (Details) - USD ($)	1 Months Ended		3 Months Ended		6 Months Ended
	Jul. 28, 2017	Jul. 31, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accounting Policies [Abstract]
Payment defaults under agreements			$ 0		$ 0
Equity contribution						$ 4,100,000
Unrealized gains, net of income taxes, recorded in AOCI			$ 7,800,000		$ 7,800,000
Dividends Payable [Line Items]
Declared dividends on common stock (dollars per share)		$ 0.22	$ 0.2425	$ 0.220	$ 0.4850	$ 0.44
Dividends declared and paid					$ 19,316,000
PNM
Dividends Payable [Line Items]
Dividends declared and paid						$ 4,100,000
Texas-New Mexico Power Company
Dividends Payable [Line Items]
Dividends declared and paid					$ 17,459,000	$ 7,500,000
Subsequent event
Dividends Payable [Line Items]
Declared dividends on common stock (dollars per share)	$ 0.2425