Significant Accounting Policies and Responsibility for Financial Statements (Policies)	9 Months Ended
	Sep. 30, 2025
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The Condensed Consolidated Financial Statements of each of TXNM, PNM, and TNMP include their accounts and those of subsidiaries in which that entity owns a majority voting interest. PNM also consolidates Valencia and ETBC I. See Note 6. PNM owns undivided interests in several jointly-owned power plants and records its pro-rata share of the assets, liabilities, and expenses for those plants. The agreements for the jointly-owned plants provide that if an owner were to default on its payment obligations, the non-defaulting owners would be responsible for their proportionate share of the obligations of the defaulting owner. In exchange, the non-defaulting owners would be entitled to their proportionate share of the generating capacity of the defaulting owner. There have been no such payment defaults under any of the agreements for the jointly-owned plants. PNMR Services Company expenses, which represent costs that are primarily driven by corporate level activities, are charged to the business segments. These services are billed at cost and are reflected as general and administrative expenses in the business segments. Other significant intercompany transactions between TXNM, PNM, and TNMP include interest and income tax sharing payments, as well as equity transactions. See Note 15. All intercompany transactions and balances have been eliminated.
New Accounting Pronouncements	New Accounting Pronouncements Information concerning recently issued accounting pronouncements that have not yet been adopted by the Company is presented below. The Company does not expect difficulty in adopting these standards by their required effective dates. Accounting Standards Update 2023-09 - Income Taxes (Topic 740): Improvements to Income Tax Disclosures In December 2023, the FASB issued ASU 2023-09 enhancing the transparency and decision usefulness of income tax disclosures. Disclosure requirements of this update include (on an annual basis) the disclosure of specific categories in the rate reconciliation and the inclusion of additional information for reconciling items that meet a quantitative threshold (if the effect of the reconciling item is equal to or greater than 5 percent of the amount computed by multiplying pre-tax income by the applicable statutory rate). The amendment also requires the disclosure (on an annual basis) of information about income taxes paid (net of refunds) including the disaggregation by federal, state, and foreign taxes as well as by individual jurisdiction. Additional requirements include the disclosure of income (loss) from continuing operations before income tax expense (benefit) disaggregated between foreign and domestic as well as income tax expense (benefit) from continuing operations disaggregated by federal, state, and foreign. ASU 2023-09 is effective for the Company for the annual reporting period beginning after December 15, 2024, with early adoption being permitted. ASU 2023-09 is to be applied on a prospective basis with retrospective application permitted. The Company expects to adopt the disclosure requirements of ASU 2023-09 with its Annual Report on Form 10-K for the year ended December 31, 2025. Accounting Standards Update 2024-03 - Income Statement (Subtopic 220-40): Reporting Comprehensive Income - Expense Disaggregation Disclosures In November 2024, the FASB issued ASU 2024-03 that will require disclosure, in the notes to the financial statements, of specified information about certain costs and expenses at each interim and annual period. Disclosures should include amounts for purchases of inventory, employee compensation, depreciation, and intangible asset amortization; certain amounts that are already required to be disclosed under GAAP in the same disclosure as other disaggregation requirements; qualitative descriptions of the amounts remaining in relevant expense categories that are not disaggregated; and the total amount of selling expenses including the entity’s definition of selling expenses. In January 2025, ASU 2025-01 was issued to clarify that the amendments of ASU 2024-03 are effective for public business entities for annual reporting periods beginning after December 15, 2026 and interim reporting periods beginning after December 15, 2027. The Company expects to adopt the disclosure requirements of ASU 2024-03 with its Annual Report on Form 10-K for the year ended December 31, 2027. Accounting Standards Update 2025-05 – Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses for Accounts Receivable and Contract Assets In July 2025, the FASB issued ASU 2025-05 that introduces a practical expedient for all entities and an accounting policy election for entities other than public business entities, related to applying Subtopic 326-20 to current accounts receivable and current contract assets arising from transactions accounted for under Topic 606. In developing a reasonable and supportable forecast as a part of estimating expected credit losses, all entities may elect a practical expedient that assumes that current conditions as of the balance sheet date do not change for the remaining life of the asset. Entities other than public business entities that elect the practical expedient are permitted to make an accounting policy election to consider collection activity after the balance sheet date when estimating expected credit losses. An entity that elects the practical expedient and the accounting policy election, if applicable, should apply the amendments in this update prospectively. The amendments in this update are effective for all entities for annual reporting periods beginning after December 15, 2025 and interim reporting periods within those annual reporting periods. Early adoption is permitted. The Company has not yet determined whether it will elect the practical expedient for estimating credit losses, however, it does not expect that this will have a material impact on its current allowance for expected credit losses. Accounting Standards Update 2025-06 – Intangibles – Goodwill and Other – Internal-Use Software (Subtopic 350-40): Targeted Improvements to the Accounting for Internal-Use Software In September 2025, the FASB issued ASU 2025-06 that updates the internal-use software guidance in subtopic 350-40 including the removal of all references to prescriptive and sequential developmental stages referred to as “project stages” throughout the subtopic. The new guidance requires an entity to start capitalizing software costs when management has authorized and committed to funding the project and it is probable that the project will be completed and used to perform the function it was intended for (referred to as the “probable-to-complete recognition threshold”). During the evaluation of the probable-to-complete recognition threshold, the entity is required to consider whether there is significant uncertainty associated with the development activities of the software. The amendments in this update are effective for all entities for annual reporting periods beginning after December 15, 2027 and interim reporting periods within those annual reporting periods. Early adoption is permitted as of the beginning of an annual reporting period. The amendments in this update permit an entity to apply the new guidance using a prospective transition approach, a modified transition approach (based on the status of a project and whether software costs were capitalized before the date of adoption), or a full retrospective transition approach. The Company has not yet determined which approach to adopt nor the impact that the new guidance will have on the accounting for its internal-use software projects.