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Summary of the Business and Significant Accounting Policies - Narrative (Details) | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2024 USD ($) utility shares | Dec. 31, 2023 USD ($) shares | Dec. 31, 2022 USD ($) | Aug. 02, 2024 shares | Aug. 01, 2024 shares
Accounting Policies Disclosures [Line Items] |  |  |  |  |
Common stock, shares authorized (in shares) | shares | 200,000,000 | 120,000,000 |  |  |
Payment defaults | $ 0 |  |  |  |
Net gains (losses) on debt securities | $ 8,639,000 | $ 4,008,000 | $ (33,392,000) |  |
TXNM |  |  |  |  |
Accounting Policies Disclosures [Line Items] |  |  |  |  |
Number of regulated utilities | utility | 2 |  |  |  |
Common stock, shares authorized (in shares) | shares |  |  |  | 200,000,000 | 120,000,000
Restricted cash |  |  | 0 |  |
PNM |  |  |  |  |
Accounting Policies Disclosures [Line Items] |  |  |  |  |
Common stock, shares authorized (in shares) | shares | 40,000,000 | 40,000,000 |  |  |
Restricted cash |  |  | 0 |  |
Allowance for funds used during construction, capitalized interest | $ 12,900,000 | $ 9,500,000 | $ 3,700,000 |  |
Allowance for funds used during construction, capitalized interest rate (as a percent) | 3.19% | 2.99% | 1.70% |  |
Allowance for equity funds used during construction | $ 13,000,000.0 | $ 9,800,000 | $ 9,300,000 |  |
Allowance for funds used during construction, capitalized cost of equity rate (as a percent) | 3.30% | 3.24% | 4.26% |  |
Net gains (losses) on debt securities | $ 17,800,000 | $ (19,100,000) | $ 25,800,000 |  |
TNMP |  |  |  |  |
Accounting Policies Disclosures [Line Items] |  |  |  |  |
Common stock, shares authorized (in shares) | shares | 12,000,000 | 12,000,000 |  |  |
Restricted cash | $ 0 | $ 0 | 0 |  |
Allowance for funds used during construction, capitalized interest | $ 8,000,000 | $ 5,700,000 | $ 3,400,000 |  |
Allowance for funds used during construction, capitalized interest rate (as a percent) | 4.14% | 3.49% | 2.25% |  |
Allowance for equity funds used during construction | $ 4,800,000 | $ 5,100,000 | $ 4,500,000 |  |
Allowance for funds used during construction, capitalized cost of equity rate (as a percent) | 2.48% | 3.17% | 2.99% |  |

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