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Fair Value of Derivative and Other Financial Instruments - Schedule of Fair Values of Investments Held by the Employee Benefit Plans and PNMR Master Trust (Details) - USD ($) $ in Thousands | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
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PNM | Pension Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | $ 379,154 | $ 407,211 | $ 410,463
PNM | Pension Plan | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 379,074 |  |
PNM | Pension Plan | Investments categorized within fair value hierarchy | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount |  | 407,717 |
PNM | Other Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 72,003 | 73,392 | 70,301
PNM | Other Postretirement Benefits | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 70,714 | 73,383 |
PNM | Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Investments categorized within fair value hierarchy | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 319,528 | 342,296 |
PNM | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Investments categorized within fair value hierarchy | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 39,538 | 50,093 |
PNM | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Cash and cash equivalents | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 825 | 2,419 |
PNM | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Mutual funds | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 38,713 | 47,674 |
PNM | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension Plan | Investments categorized within fair value hierarchy | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 106,220 | 136,474 |
PNM | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount |  | 46,122 |
PNM | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Investments categorized within fair value hierarchy | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 39,538 |  |
PNM | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Cash and cash equivalents | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 825 | 2,419 |
PNM | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Mutual funds | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 38,713 | 43,703 |
PNM | Significant Other Observable Inputs (Level 2) | Pension Plan | Investments categorized within fair value hierarchy | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 213,308 | 205,822 |
PNM | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount |  | 3,971 |
PNM | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Investments categorized within fair value hierarchy | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 0 |  |
PNM | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Cash and cash equivalents | Estimate of Fair Value Measurement | 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 | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 0 | 3,971 |
PNM | Fair Value Measured at Net Asset Value Per Share | Pension Plan | Uncategorized investments | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 59,546 | 65,421 |
PNM | Fair Value Measured at Net Asset Value Per Share | Other Postretirement Benefits | Uncategorized investments | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 31,176 | 23,290 |
TNMP | Pension Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 38,225 | 41,353 | 43,447
TNMP | Pension Plan | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 38,166 |  |
TNMP | Pension Plan | Investments categorized within fair value hierarchy | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount |  | 41,128 |
TNMP | Other Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 7,542 | 8,353 | $ 8,718
TNMP | Other Postretirement Benefits | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 7,582 |  |
TNMP | Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Investments categorized within fair value hierarchy | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 33,294 | 35,870 |
TNMP | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount |  | 8,403 |
TNMP | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Cash and cash equivalents | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 111 | 162 |
TNMP | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Mutual funds | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 6,987 | 8,241 |
TNMP | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Investments Categorized Within Fair Value Hierarchy | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 7,098 |  |
TNMP | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension Plan | Investments categorized within fair value hierarchy | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 7,543 | 12,192 |
TNMP | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount |  | 7,968 |
TNMP | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Cash and cash equivalents | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 111 | 162 |
TNMP | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Mutual funds | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 6,987 | 7,806 |
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 | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 7,098 |  |
TNMP | Significant Other Observable Inputs (Level 2) | Pension Plan | Investments categorized within fair value hierarchy | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 25,751 | 23,678 |
TNMP | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount |  | 435 |
TNMP | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Cash and cash equivalents | Estimate of Fair Value Measurement | 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 | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 0 | 435 |
TNMP | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Investments Categorized Within Fair Value Hierarchy | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 0 |  |
TNMP | Fair Value Measured at Net Asset Value Per Share | Pension Plan | Uncategorized investments | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 4,872 | 5,258 |
TNMP | Fair Value Measured at Net Asset Value Per Share | Other Postretirement Benefits | Uncategorized investments | Estimate of Fair Value Measurement | Recurring Basis |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 484 |  |
TXNM |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | $ 417,240 | $ 448,845 |
TXNM | 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 |
TXNM | 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 |
TXNM | 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 |
TXNM | Fair Value, Inputs, Level 1, 2 and 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | $ 352,822 | $ 378,166 |
TXNM | Fair Value, Inputs, Level 1, 2 and 3 | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 10,981 | 13,995 |
TXNM | Fair Value, Inputs, Level 1, 2 and 3 | Mutual funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 146,858 | 159,281 |
TXNM | Fair Value, Inputs, Level 1, 2 and 3 | Corporate stocks, common |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 34,418 | 27,167 |
TXNM | Fair Value, Inputs, Level 1, 2 and 3 | Corporate stocks, preferred |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 0 | 741 |
TXNM | Fair Value, Inputs, Level 1, 2 and 3 | U.S. government |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 56,303 | 61,684 |
TXNM | Fair Value, Inputs, Level 1, 2 and 3 | International government |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 0 | 4,713 |
TXNM | Fair Value, Inputs, Level 1, 2 and 3 | Municipals |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 4,718 | 5,071 |
TXNM | Fair Value, Inputs, Level 1, 2 and 3 | Corporate and other |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 99,544 | 105,514 |
TXNM | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 113,763 | 148,666 |
TXNM | 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 | 10,981 | 13,995 |
TXNM | Quoted Prices in Active Markets for Identical Assets (Level 1) | Mutual funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 45,333 | 49,219 |
TXNM | 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 | 34,418 | 27,167 |
TXNM | 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 | 0 | 741 |
TXNM | 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 | 23,031 | 57,544 |
TXNM | 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 |
TXNM | 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 |
TXNM | 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 |
TXNM | Significant Other Observable Inputs (Level 2) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 239,059 | 229,500 |
TXNM | Significant Other Observable Inputs (Level 2) | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 0 | 0 |
TXNM | Significant Other Observable Inputs (Level 2) | Mutual funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 101,525 | 110,062 |
TXNM | Significant Other Observable Inputs (Level 2) | Corporate stocks, common |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 0 | 0 |
TXNM | Significant Other Observable Inputs (Level 2) | Corporate stocks, preferred |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 0 | 0 |
TXNM | Significant Other Observable Inputs (Level 2) | U.S. government |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 33,272 | 4,140 |
TXNM | Significant Other Observable Inputs (Level 2) | International government |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 0 | 4,713 |
TXNM | Significant Other Observable Inputs (Level 2) | Municipals |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 4,718 | 5,071 |
TXNM | Significant Other Observable Inputs (Level 2) | Corporate and other |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 99,544 | 105,514 |
TXNM | Fair Value Measured at Net Asset Value Per Share | Private equity funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 2,846 | 5,617 |
TXNM | Fair Value Measured at Net Asset Value Per Share | Hedge funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | 34,126 | 35,137 |
TXNM | Fair Value Measured at Net Asset Value Per Share | Real estate funds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, plan assets, amount | $ 27,446 | $ 29,925 |

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