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Pension and Other Postretirement Benefits - Assumptions Used (Details) | 12 Months Ended
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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%

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- 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 + Details
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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 + Details
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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 + Details
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