Pension and Other Postretirement Benefit Plans (Details) (USD $)	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Public Service Company of New Mexico [Member] \| Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	$ 0	$ 0
Interest cost	7,064,000	7,541,000
Expected return on plan assets	(9,831,000)	(9,511,000)
Amortization of net (gain) loss	3,705,000	3,255,000
Amortization of prior service cost	(241,000)	(241,000)
Net Periodic Benefit Cost (Income)	697,000	1,044,000
Defined Benefit Plan, Contributions by Employer	30,000,000	0
Defined Benefit Plan, Estimated Future Employer Contributions After Current Fiscal Year	22,000,000
Public Service Company of New Mexico [Member] \| Pension Plan [Member] \| Minimum [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate (as a percent)	4.80%
Public Service Company of New Mexico [Member] \| Pension Plan [Member] \| Maximum [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate (as a percent)	5.50%
Public Service Company of New Mexico [Member] \| OPEB [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	51,000	45,000
Interest cost	1,022,000	1,159,000
Expected return on plan assets	(1,403,000)	(1,410,000)
Amortization of net (gain) loss	491,000	556,000
Amortization of prior service cost	(160,000)	(336,000)
Net Periodic Benefit Cost (Income)	1,000	14,000
Defined Benefit Plan, Contributions by Employer	800,000	800,000
Defined Benefit Plan, Estimated Future Employer Contributions After Current Fiscal Year	14,000,000
Defined Benefit Plan Total Expected Employer Contributions for Fiscal Year	3,500,000
Public Service Company of New Mexico [Member] \| Executive Retirement Program [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0	0
Interest cost	190,000	205,000
Expected return on plan assets	0	0
Amortization of net (gain) loss	81,000	52,000
Amortization of prior service cost	0	0
Net Periodic Benefit Cost (Income)	271,000	257,000
Defined Benefit Plan, Contributions by Employer	500,000	400,000
Defined Benefit Plan Total Expected Employer Contributions for Fiscal Year	1,500,000
Texas-New Mexico Power Company [Member] \| Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0	0
Interest cost	761,000	798,000
Expected return on plan assets	(1,105,000)	(1,132,000)
Amortization of net (gain) loss	195,000	166,000
Amortization of prior service cost	0	0
Net Periodic Benefit Cost (Income)	(149,000)	(168,000)
Defined Benefit Plan, Estimated Future Employer Contributions After Current Fiscal Year	0
Texas-New Mexico Power Company [Member] \| Pension Plan [Member] \| Minimum [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate (as a percent)	4.80%
Texas-New Mexico Power Company [Member] \| Pension Plan [Member] \| Maximum [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate (as a percent)	5.50%
Texas-New Mexico Power Company [Member] \| OPEB [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	62,000	59,000
Interest cost	152,000	155,000
Expected return on plan assets	(130,000)	(133,000)
Amortization of net (gain) loss	0	(31,000)
Amortization of prior service cost	0	8,000
Net Periodic Benefit Cost (Income)	84,000	58,000
Defined Benefit Plan, Contributions by Employer	0	0
Defined Benefit Plan, Estimated Future Employer Contributions After Current Fiscal Year	1,400,000
Defined Benefit Plan Total Expected Employer Contributions for Fiscal Year	300,000
Texas-New Mexico Power Company [Member] \| Executive Retirement Program [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0	0
Interest cost	9,000	10,000
Expected return on plan assets	0	0
Amortization of net (gain) loss	1,000	0
Amortization of prior service cost	0	0
Net Periodic Benefit Cost (Income)	10,000	10,000
Defined Benefit Plan Total Expected Employer Contributions for Fiscal Year	100,000
Texas-New Mexico Power Company [Member] \| Executive Retirement Program [Member] \| Maximum [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Contributions by Employer	$ 100,000	$ 100,000

Defined Benefit Plan, Estimated Future Employer Contributions After Current Fiscal Year

No definition available.

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- Definition

Defined Benefit Plan Total Expected Employer Contributions for Fiscal Year

+ References

No definition available.

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- Definition

The amount of gains or losses recognized in net periodic benefit cost.

+ References

+ Details

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- Definition

The amount of the prior service cost or credit recognized in net periodic benefit cost relating to benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation.

+ References

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- Definition

The interest rate used to adjust for the time value of money.

+ References

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- Definition

The increase in the fair value of plan assets from contributions made by the employer.

+ References

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- Definition

An amount calculated as a basis for determining the extent of delayed recognition of the effects of changes in the fair value of assets. The expected return on plan assets is determined based on the expected long-term rate of return on plan assets and the market-related value of plan assets.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Glossary Expected Return on Plan Assets

-URI http://asc.fasb.org/extlink&oid=6512136

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 60

-Glossary Expected Return on Plan Assets

-URI http://asc.fasb.org/extlink&oid=6512171

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (h)(3)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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- Definition

The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

+ References

+ Details

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- Definition

The total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments.

+ References

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- Definition

The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (h)(1)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Service Cost (Component of Net Periodic Pension Cost)

-URI http://asc.fasb.org/extlink&oid=6525008

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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