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Pension and Other Postretirement Benefits - Schedule of Weighted-Average Assumptions of PBO, APBO and Executive Retirement Programs (Details) | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items] |  |  |
Expected return on plan assets | 4.00% |  |
PNM | Pension Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate for determining | 5.78% | 5.46% | 5.74%
Discount rate for determining net periodic benefit cost | 5.46% | 5.74% | 3.00%
Expected return on plan assets | 6.86% | 6.30% | 5.50%
PNM | Other Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate for determining | 5.78% | 5.48% | 5.75%
Discount rate for determining net periodic benefit cost | 5.48% | 5.75% | 2.99%
Expected return on plan assets | 6.60% | 5.90% | 4.75%
PNM | Executive Retirement Program |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate for determining | 5.78% | 5.45% | 5.73%
Discount rate for determining net periodic benefit cost | 5.45% | 5.73% | 3.02%
TNMP | Pension Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate for determining | 5.78% | 5.47% | 5.75%
Discount rate for determining net periodic benefit cost | 5.47% | 5.75% | 3.01%
Expected return on plan assets | 5.95% | 5.50% | 4.40%
TNMP | Other Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate for determining | 5.78% | 5.48% | 5.75%
Discount rate for determining net periodic benefit cost | 5.48% | 5.75% | 2.99%
Expected return on plan assets | 5.25% | 4.70% | 3.80%
TNMP | Executive Retirement Program |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate for determining |  | 5.47% | 5.75%
Discount rate for determining net periodic benefit cost | 5.47% | 5.75% | 3.01%

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- 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 -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (k)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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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 -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (k)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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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 -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 8 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-8 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (k)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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