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Pension and Other Postretirement Benefits - Assumptions Used (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	4.00%
Public Service Company of New Mexico | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Discount rate for determining PBO and APBO	2.66%	3.42%	4.65%
Discount rate for determining net periodic benefit cost (income)	3.42%	4.65%	4.05%
Expected return on plan assets	5.90%	6.86%	6.54%
Public Service Company of New Mexico | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate for determining PBO and APBO	2.65%	3.42%	4.63%
Discount rate for determining net periodic benefit cost (income)	3.42%	4.63%	4.00%
Expected return on plan assets	7.00%	7.20%	7.42%
Public Service Company of New Mexico | Executive Retirement Program
Defined Benefit Plan Disclosure [Line Items]
Discount rate for determining PBO and APBO	2.68%	3.44%	4.66%
Discount rate for determining net periodic benefit cost (income)	3.44%	4.66%	4.05%
Texas-New Mexico Power Company | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Discount rate for determining PBO and APBO	2.69%	3.46%	4.63%
Discount rate for determining net periodic benefit cost (income)	3.46%	4.63%	4.01%
Expected return on plan assets	5.90%	6.90%	6.57%
Texas-New Mexico Power Company | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate for determining PBO and APBO	2.65%	3.42%	4.63%
Discount rate for determining net periodic benefit cost (income)	3.42%	4.63%	4.00%
Expected return on plan assets	5.60%	5.80%	5.86%
Texas-New Mexico Power Company | Executive Retirement Program
Defined Benefit Plan Disclosure [Line Items]
Discount rate for determining PBO and APBO	2.69%	3.46%	4.63%
Discount rate for determining net periodic benefit cost (income)	3.46%	4.63%	4.01%

X

- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(1)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(1)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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- Definition

Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2919-114920

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