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Pension and Other Postretirement Benefits - Assumptions Used (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	4.00%
Public Service Company of New Mexico [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for determining PBO and APBO	4.51%	5.29%	4.48%
Discount rate for determining net periodic benefit cost (income)	5.29%	4.48%	5.27%
Expected return on plan assets	6.50%	6.80%	7.20%
Public Service Company of New Mexico [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for determining PBO and APBO	4.47%	5.34%	4.45%
Discount rate for determining net periodic benefit cost (income)	5.34%	4.45%	5.21%
Expected return on plan assets	7.70%	7.70%	8.50%
Public Service Company of New Mexico [Member] | Executive Retirement Program [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for determining PBO and APBO	4.51%	5.29%	4.48%
Discount rate for determining net periodic benefit cost (income)	5.29%	4.48%	5.27%
Texas-New Mexico Power Company [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for determining PBO and APBO	4.49%	5.39%	4.39%
Discount rate for determining net periodic benefit cost (income)	5.39%	4.39%	5.06%
Expected return on plan assets	6.50%	6.80%	7.20%
Texas-New Mexico Power Company [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for determining PBO and APBO	4.47%	5.34%	4.45%
Discount rate for determining net periodic benefit cost (income)	5.34%	4.45%	5.21%
Expected return on plan assets	5.70%	5.70%	6.50%
Texas-New Mexico Power Company [Member] | Executive Retirement Program [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for determining PBO and APBO	4.49%	5.39%	4.39%
Discount rate for determining net periodic benefit cost (income)	5.39%	4.39%	5.06%

X

- Definition

The interest rate used to adjust for the time value of money for 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 (k)(1)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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- Definition

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

+ 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 (k)(1)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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- Definition

An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Expected Long-Term Rate of Return on Plan Assets
-URI http://asc.fasb.org/extlink&oid=6512046

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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- 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.

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