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Significant Accounting Policies and Responsibility for Financial Statements (Details)	Mar. 31, 2017 USD ($)
Accounting Policies [Abstract]
Payment defaults under agreements	$ 0
Unrealized gains, net of income taxes, recorded in AOCI	$ 6,800,000

X

- Definition

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

+ References

No definition available.

+ Details

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

X

- 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

X

- References

No definition available.

+ Details

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