Additional Leased Capacity to be Purchased

No definition available.

Name:	pnm_AdditionalLeasedCapacitytobePurchased
Namespace Prefix:	pnm_
Data Type:	num:powerItemType
Balance Type:	na
Period Type:	instant

- Definition

Annual lease payments

+ References

No definition available.

+ Details

Name:	pnm_AnnualLeasePayments
Namespace Prefix:	pnm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Annual Lease Payments During Renewal Period

+ References

No definition available.

+ Details

Name:	pnm_AnnualLeasePaymentsDuringRenewalPeriod
Namespace Prefix:	pnm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Lease Covenant, Restriction on Conveying, Transferring, Leasing, & Dividends

+ References

No definition available.

+ Details

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

- Definition

Leased Capacity to be Purchased

+ References

No definition available.

+ Details

Name:	pnm_LeasedCapacitytobePurchased
Namespace Prefix:	pnm_
Data Type:	num:powerItemType
Balance Type:	na
Period Type:	instant

- Definition

Operating Lease, Extended Term

+ References

No definition available.

+ Details

Name:	pnm_OperatingLeaseExtendedTerm
Namespace Prefix:	pnm_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Operating Leases, Number of leases set to expire

+ References

No definition available.

+ Details

Name:	pnm_OperatingLeasesNumberofleasessettoexpire
Namespace Prefix:	pnm_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Operating Leases, Period To Notify Of Lease Retention

+ References

No definition available.

+ Details

Name:	pnm_OperatingLeasesPeriodToNotifyOfLeaseRetention
Namespace Prefix:	pnm_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Operating Leases, Period to expiration of the lease

+ References

No definition available.

+ Details

Name:	pnm_OperatingLeasesPeriodtoexpirationofthelease
Namespace Prefix:	pnm_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Operating Leases, Renewal Options After Original Lease Term

+ References

No definition available.

+ Details

Name:	pnm_OperatingLeasesRenewalOptionsAfterOriginalLeaseTerm
Namespace Prefix:	pnm_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Operating Leases of Lessee, Number of Leases

+ References

No definition available.

+ Details

Name:	pnm_OperatingLeasesofLesseeNumberofLeases
Namespace Prefix:	pnm_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Operating Leases of Lessee, Number of Lessors

+ References

No definition available.

+ Details

Name:	pnm_OperatingLeasesofLesseeNumberofLessors
Namespace Prefix:	pnm_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Public Utilities, Additional ownership percentage in EIP acquired

+ References

No definition available.

+ Details

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

- Definition

Public Utilities, Lease ownership percentage in EIP

+ References

No definition available.

+ Details

Name:	pnm_PublicUtilitiesLeaseOwnershipPercentageInEip
Namespace Prefix:	pnm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Public Utilities, Option to Purchase Leased Capacity At Fair Value

+ References

No definition available.

+ Details

Name:	pnm_PublicUtilitiesOptionToPurchaseLeasedCapacityAtFairValue
Namespace Prefix:	pnm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Purchase Price of Leased Asset

+ References

No definition available.

+ Details

Name:	pnm_PurchasePriceofLeasedAsset
Namespace Prefix:	pnm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Rental Payments, Fixed renewal option period during original terms of leases

+ References

No definition available.

+ Details

Name:	pnm_RentalPaymentsFixedRenewalOptionPeriodDuringOriginalTermsOfLeases
Namespace Prefix:	pnm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The difference between the maximum amount of estimated loss and the amount recorded as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 05
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6395354&loc=d3e12631-108344

+ Details

Name:	us-gaap_LossContingencyRangeOfPossibleLossPortionNotAccrued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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

- Details

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

- Details

Name:	pnm_CommitmentsAndContingenciesRelatedToEnvironmentAndOtherNatureAxis=pnm_TgpGranadaLlcAndItsAffiliateComplaintMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LeaseArrangementTypeAxis=pnm_NavajoNationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_LeaseArrangementTypeAxis=pnm_PaloVerdeNuclearGeneratingStationUnit1LeasesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LeaseArrangementTypeAxis=pnm_PaloVerdeNuclearGeneratingStationUnit2LeasesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LeaseArrangementTypeAxis=pnm_PaloVerdeNuclearGeneratingStationUnit1LeasewithMaximumOptionPeriodProvisionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LeaseArrangementTypeAxis=pnm_PaloVerdeNuclearGeneratingStationUnit2LeasewithMaximumOptionPeriodProvisionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LeaseArrangementTypeAxis=pnm_PaloVerdeNuclearGeneratingStationUnit1LeaseExpiresin2023Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LeaseArrangementTypeAxis=pnm_PaloVerdeNuclearGeneratingStationUnit2LeaseExpiresin2024Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LeaseArrangementTypeAxis=pnm_PaloVerdeNuclearGeneratingStationUnit2Leases32.76MWMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Lease Commitments - Narrative (Details) $ in Millions		12 Months Ended
Lease Commitments - Narrative (Details) $ in Millions	Jan. 15, 2016 USD ($) lease MW	Dec. 31, 2017 USD ($) lease lessor	Apr. 01, 2015 USD ($)	Jan. 15, 2015 lease	Dec. 31, 1986 lease	Dec. 31, 1985 lease
Lease commitments
Operating lease, option term extensions		2 years
Operating leases, renewal options after original lease term		6 years
Operating leases, period to notify of lease retention		3 years
Public Service Company of New Mexico \| TGP Granada, LLC and its affiliate Complaint
Lease commitments
Lease ownership in EIP		60.00%
Additional area leased of the EIP			40.00%
Option to purchase leased capacity at fair value			$ 7.7
Public Service Company of New Mexico \| Navajo Nation
Lease commitments
Number of operating leases set to expire \| lease		0
Operating leases, period to expiration of the lease		5 years
Annual lease payments		$ 6.0
Public Service Company of New Mexico \| Palo Verde Nuclear Generating Station
Lease commitments
Number of leases \| lease					4	4
Rental payments, fixed renewal option period during original terms of leases		50.00%
Lease covenants, restrictions on conveying, transferring, leasing, and dividends (more than)		5.00%
Loss contingency, range of possible loss, portion not accrued (up to)		$ 169.9
Public Service Company of New Mexico \| Palo Verde Nuclear Generating Station, Unit 1 Leases
Lease commitments
Annual lease payments		33.0
Number of leases \| lease				4		4
Annual lease payments during renewal period		16.5
Public Service Company of New Mexico \| Palo Verde Nuclear Generating Station, Unit 2 Leases
Lease commitments
Annual lease payments		$ 23.7
Number of leases \| lease	1	3			4
Annual lease payments during renewal period		$ 1.6
Estimated purchase price of leased asset	$ 78.1
Leased capacity to be purchased (in megawatts) \| MW	31.25
Public Service Company of New Mexico \| Palo Verde Nuclear Generating Station, Unit 1, Lease with Maximum Option Period Provision
Lease commitments
Number of lessors \| lessor		4
Public Service Company of New Mexico \| Palo Verde Nuclear Generating Station, Unit 2, Lease with Maximum Option Period Provision
Lease commitments
Number of leases \| lease		1
Public Service Company of New Mexico \| Palo Verde Nuclear Generating Station, Unit 1, Lease Expires in 2023
Lease commitments
Number of leases \| lease		4
Public Service Company of New Mexico \| Palo Verde Nuclear Generating Station, Unit 2, Lease Expires in 2024
Lease commitments
Number of leases \| lease		1
Public Service Company of New Mexico \| Palo Verde Nuclear Generating Station, Unit 2 Leases 32.76 MW
Lease commitments
Number of leases \| lease	2
Estimated purchase price of leased asset	$ 85.2
Additional capacity to be leased (in megawatts) \| MW	32.76