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Fair Value of Derivative and Other Financial Instruments - Defined Benefit Plans Disclosure (Details) - USD ($) $ in Thousands | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
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PNM | Pension Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | $ 407,211 | $ 410,463 | $ 576,707
PNM | Pension Plan | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 407,717 |  |
PNM | Pension Plan | Participation in PNMR Master Trust Investments: | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount |  | 409,970 |
PNM | Other Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 73,392 | 70,301 | 95,805
PNM | Other Postretirement Benefits | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 73,383 |  |
PNM | Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Participation in PNMR Master Trust Investments: | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 342,296 | 342,183 |
PNM | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount |  | 70,704 |
PNM | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Cash and cash equivalents | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 2,419 | 1,703 |
PNM | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Mutual funds | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 47,674 | 69,001 |
PNM | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension Plan | Participation in PNMR Master Trust Investments: | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 136,474 | 143,911 |
PNM | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount |  | 43,771 |
PNM | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Cash and cash equivalents | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 2,419 | 1,703 |
PNM | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Mutual funds | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 43,703 | 42,068 |
PNM | Significant Other Observable Inputs (Level 2) | Pension Plan | Participation in PNMR Master Trust Investments: | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 205,822 | 198,272 |
PNM | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount |  | 26,933 |
PNM | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Cash and cash equivalents | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 0 | 0 |
PNM | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Mutual funds | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 3,971 | 26,933 |
PNM | Fair Value Measured at Net Asset Value Per Share | Pension Plan | Uncategorized Investment | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 65,421 | 67,787 |
PNM | Fair Value Measured at Net Asset Value Per Share | Other Postretirement Benefits | Uncategorized Investment | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 23,290 |  |
TNMP | Pension Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 41,353 | 43,447 | 62,942
TNMP | Pension Plan | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 41,128 |  |
TNMP | Pension Plan | Participation in PNMR Master Trust Investments: | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount |  | 44,050 |
TNMP | Other Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 8,353 | 8,718 | $ 12,593
TNMP | Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Participation in PNMR Master Trust Investments: | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 35,870 | 38,617 |
TNMP | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount |  | 8,722 |
TNMP | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Participation in PNMR Master Trust Investments: | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 50,093 |  |
TNMP | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Cash and cash equivalents | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 162 | 149 |
TNMP | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Mutual funds | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 8,241 | 8,573 |
TNMP | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Investments Categorized Within Fair Value Hierarchy | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 8,403 |  |
TNMP | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension Plan | Participation in PNMR Master Trust Investments: | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 12,192 | 13,556 |
TNMP | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount |  | 8,167 |
TNMP | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Participation in PNMR Master Trust Investments: | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 46,122 |  |
TNMP | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Cash and cash equivalents | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 162 | 149 |
TNMP | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Mutual funds | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 7,806 | 8,018 |
TNMP | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Investments Categorized Within Fair Value Hierarchy | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 7,968 |  |
TNMP | Significant Other Observable Inputs (Level 2) | Pension Plan | Participation in PNMR Master Trust Investments: | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 23,678 | 25,061 |
TNMP | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount |  | 555 |
TNMP | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Participation in PNMR Master Trust Investments: | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 3,971 |  |
TNMP | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Cash and cash equivalents | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 0 | 0 |
TNMP | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Mutual funds | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 435 | 555 |
TNMP | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Investments Categorized Within Fair Value Hierarchy | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 435 |  |
TNMP | Fair Value Measured at Net Asset Value Per Share | Pension Plan | Uncategorized Investment | Estimate of Fair Value Measurement | Measured on a recurring basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 5,258 | 5,433 |
PNMR |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | $ 448,845 | $ 454,020 |
PNMR | Private equity funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Fair Value by Hierarchy and NAV [Extensible List] | Fair Value Measured at Net Asset Value Per Share | Fair Value Measured at Net Asset Value Per Share |
PNMR | Hedge funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Fair Value by Hierarchy and NAV [Extensible List] | Fair Value Measured at Net Asset Value Per Share | Fair Value Measured at Net Asset Value Per Share |
PNMR | Real estate funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Fair Value by Hierarchy and NAV [Extensible List] | Fair Value Measured at Net Asset Value Per Share | Fair Value Measured at Net Asset Value Per Share |
PNMR | Fair Value, Inputs, Level 1, 2 and 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | $ 378,166 | $ 380,800 |
PNMR | Fair Value, Inputs, Level 1, 2 and 3 | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 13,995 | 17,106 |
PNMR | Fair Value, Inputs, Level 1, 2 and 3 | Corporate stocks, common |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 27,167 | 53,661 |
PNMR | Fair Value, Inputs, Level 1, 2 and 3 | Corporate stocks, preferred |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 741 | 639 |
PNMR | Fair Value, Inputs, Level 1, 2 and 3 | Mutual funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 159,281 | 135,200 |
PNMR | Fair Value, Inputs, Level 1, 2 and 3 | U.S. government |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 61,684 | 62,637 |
PNMR | Fair Value, Inputs, Level 1, 2 and 3 | International government |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 4,713 | 3,318 |
PNMR | Fair Value, Inputs, Level 1, 2 and 3 | Municipals |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 5,071 | 4,922 |
PNMR | Fair Value, Inputs, Level 1, 2 and 3 | Corporate and other |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 105,514 | 103,317 |
PNMR | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 148,666 | 157,467 |
PNMR | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 13,995 | 17,106 |
PNMR | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate stocks, common |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 27,167 | 53,661 |
PNMR | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate stocks, preferred |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 741 | 639 |
PNMR | Quoted Prices in Active Markets for Identical Assets (Level 1) | Mutual funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 49,219 | 27,412 |
PNMR | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. government |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 57,544 | 58,649 |
PNMR | Quoted Prices in Active Markets for Identical Assets (Level 1) | International government |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 0 | 0 |
PNMR | Quoted Prices in Active Markets for Identical Assets (Level 1) | Municipals |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 0 | 0 |
PNMR | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate and other |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 0 | 0 |
PNMR | Significant Other Observable Inputs (Level 2) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 229,500 | 223,333 |
PNMR | Significant Other Observable Inputs (Level 2) | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 0 | 0 |
PNMR | Significant Other Observable Inputs (Level 2) | Corporate stocks, common |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 0 | 0 |
PNMR | Significant Other Observable Inputs (Level 2) | Corporate stocks, preferred |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 0 | 0 |
PNMR | Significant Other Observable Inputs (Level 2) | Mutual funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 110,062 | 107,788 |
PNMR | Significant Other Observable Inputs (Level 2) | U.S. government |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 4,140 | 3,988 |
PNMR | Significant Other Observable Inputs (Level 2) | International government |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 4,713 | 3,318 |
PNMR | Significant Other Observable Inputs (Level 2) | Municipals |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 5,071 | 4,922 |
PNMR | Significant Other Observable Inputs (Level 2) | Corporate and other |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 105,514 | 103,317 |
PNMR | Fair Value Measured at Net Asset Value Per Share | Private equity funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 5,617 | 6,691 |
PNMR | Fair Value Measured at Net Asset Value Per Share | Hedge funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 35,137 | 33,258 |
PNMR | Fair Value Measured at Net Asset Value Per Share | Real estate funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | $ 29,925 | $ 33,271 |

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- Definition Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee. + 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 50 -Paragraph 1 -Subparagraph (d)(iv)(02) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -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 (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 6: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 7: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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- Definition Indicates level within fair value hierarchy and fair value measured at net asset value per share as practical expedient, of defined benefit plan asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(03) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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