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Pension and Other Postretirement Benefit Plans - Schedule of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023
PNM | Pension Plan |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service cost | $ 0 | $ 0 | $ 0 | $ 0
Interest cost | 5,427 | 5,913 | 16,282 | 17,740
Expected return on plan assets | (7,758) | (7,299) | (23,272) | (21,897)
Amortization of net (gain) loss | 2,661 | 2,646 | 7,984 | 7,937
Amortization of prior service cost | 0 | 0 | 0 | 0
Net Periodic Benefit Cost (Income) | 330 | 1,260 | 994 | 3,780
PNM | OPEB Plan |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service cost | 0 | 0 | 0 | 0
Interest cost | 597 | 675 | 1,791 | 2,027
Expected return on plan assets | (1,391) | (1,242) | (4,173) | (3,727)
Amortization of net (gain) loss | 0 | 0 | 0 | 0
Amortization of prior service cost | 0 | 0 | 0 | 0
Net Periodic Benefit Cost (Income) | (794) | (567) | (2,382) | (1,700)
PNM | Executive Retirement Program |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service cost | 0 | 0 | 0 | 0
Interest cost | 124 | 135 | 372 | 405
Expected return on plan assets | 0 | 0 | 0 | 0
Amortization of net (gain) loss | 50 | 38 | 150 | 114
Amortization of prior service cost | 0 | 0 | 0 | 0
Net Periodic Benefit Cost (Income) | 174 | 173 | 522 | 519
Texas-New Mexico Power Company | Pension Plan |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service cost | 0 | 0 | 0 | 0
Interest cost | 553 | 601 | 1,660 | 1,802
Expected return on plan assets | (687) | (674) | (2,061) | (2,023)
Amortization of net (gain) loss | 139 | 110 | 417 | 329
Amortization of prior service cost | 0 | 0 | 0 | 0
Net Periodic Benefit Cost (Income) | 5 | 37 | 16 | 108
Texas-New Mexico Power Company | OPEB Plan |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service cost | 5 | 5 | 16 | 16
Interest cost | 96 | 106 | 289 | 319
Expected return on plan assets | (129) | (120) | (386) | (361)
Amortization of net (gain) loss | (161) | (190) | (482) | (570)
Amortization of prior service cost | 0 | 0 | 0 | 0
Net Periodic Benefit Cost (Income) | (189) | (199) | (563) | (596)
Texas-New Mexico Power Company | Executive Retirement Program |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service cost | 0 | 0 | 0 | 0
Interest cost | 4 | 3 | 12 | 9
Expected return on plan assets | 0 | 0 | 0 | 0
Amortization of net (gain) loss | 0 | 0 | 0 | 0
Amortization of prior service cost | 0 | 0 | 0 | 0
Net Periodic Benefit Cost (Income) | $ 4 | $ 3 | $ 12 | $ 9

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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 3A -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480535/715-20-45-3A Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-18 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (h)(4) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a)(4) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-6 + Details
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- Definition Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 3A -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480535/715-20-45-3A Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-18 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (h)(5) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a)(5) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-6 + Details
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- Definition Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 3A -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480535/715-20-45-3A Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-18 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (h)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-6 + Details
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- Definition Amount of cost recognized for passage of time related to defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 3A -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480535/715-20-45-3A Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-18 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (h)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-6 + Details
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