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Pension and Other Postretirement Benefits - Narrative (Details) - USD ($) |  | 12 Months Ended
--- | --- | ---
Jan. 01, 2018 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Expected return on plan assets |  | 4.00% |  |
Amortization of gains and losses that are outside the corridor |  | 5 years |  |
Maximum annual contributions per employee (as a percent) |  | 75.00% |  |
Employer matching contribution, percent of employees' gross pay (as a percent) |  | 6.00% |  |
Minimum |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Non-matching contribution of eligible compensation based on eligible employee's age (as a percent) |  | 3.00% |  |
Maximum |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Non-matching contribution of eligible compensation based on eligible employee's age (as a percent) |  | 10.00% |  |
PNM |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Rate of return (as a percent) |  | 3.33% |  |
TNMP |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Rate of return (as a percent) |  | 0.62% |  |
Pension Plan |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Expected long-term return resulting from effect of 1% change |  | 1.00% |  |
Expected long-term return resulting from effect of one-percentage point increase |  | 1.00% |  |
Expected future employer contributions, year one through four |  | $ 0 |  |
Expected future employer contributions, year five |  | $ 7,900,000 |  |
Weighted average discount rate related to anticipated contributions (as a percent) |  | 5.35% |  |
Pension Plan | Equity Securities |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Investment allocation targets (as a percent) |  | 35.00% |  |
Pension Plan | Fixed Income |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Investment allocation targets (as a percent) |  | 50.00% |  |
Pension Plan | Alternative Investments |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Investment allocation targets (as a percent) |  | 15.00% |  |
Pension Plan | PNM |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Expected return on plan assets |  | 6.86% | 6.30% | 5.50%
Expected long-term return on assets decrease resulting in increase net periodic costs In next fiscal year |  | $ 4,100,000 |  |
Actuarial gains (losses) recorded as regulatory assets and liabilities |  | (12,081,000) |  |
Employer contributions |  | $ 1,000 | $ 0 |
Pension Plan | TNMP |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Expected return on plan assets |  | 5.95% | 5.50% | 4.40%
Expected long-term return on assets decrease resulting in increase net periodic costs In next fiscal year |  | $ 400,000 |  |
Actuarial gains (losses) recorded as regulatory assets and liabilities |  | (456,000) |  |
Employer contributions |  | $ 151,000 | $ 0 |
Pension Plan | TNMP | Equity Securities |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Investment allocation targets (as a percent) |  | 16.00% |  |
Pension Plan | TNMP | Fixed Income |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Investment allocation targets (as a percent) |  | 70.00% |  |
Pension Plan | TNMP | Alternative Investments |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Investment allocation targets (as a percent) |  | 14.00% |  |
Other Postretirement Benefits |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Expected long-term return resulting from effect of 1% change |  | 1.00% |  |
Other Postretirement Benefits | Equity Securities |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Investment allocation targets (as a percent) |  | 30.00% |  |
Other Postretirement Benefits | Fixed Income |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Investment allocation targets (as a percent) |  | 70.00% |  |
Other Postretirement Benefits | PNM |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Expected return on plan assets |  | 6.60% | 5.90% | 4.75%
Expected long-term return on assets decrease resulting in increase net periodic costs In next fiscal year |  | $ 800,000 |  |
Rate of return (as a percent) |  | 4.50% |  |
Actuarial gains (losses) recorded as regulatory assets and liabilities |  | $ (100,000) |  |
Employer matching contribution, maximum | 5.00% |  |  |
Employer contributions |  | 193,000 | $ 157,000 |
Expected employer contributions in current fiscal year |  | $ 100,000 | $ 0 |
Other Postretirement Benefits | TNMP |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Expected return on plan assets |  | 5.25% | 4.70% | 3.80%
Expected long-term return on assets decrease resulting in increase net periodic costs In next fiscal year |  | $ 100,000 |  |
Rate of return (as a percent) |  | 0.30% |  |
Actuarial gains (losses) recorded as regulatory assets and liabilities |  | $ (300,000) |  |
Effect of 1%-point change in assumed health care cost trend rates on net periodic expense and APBO |  | 0 |  |
Employer contributions |  | 0 | $ 0 |
Expected employer contributions in current fiscal year |  | 200,000 | 0 |
Other Postretirement Benefits | PNM and TNMP |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Expected employer contributions in fiscal year through year 5 |  | 0 |  |
Expected employer disbursements for next fiscal year |  | 2,000,000.0 |  |
Expected employer disbursements by employer in year 2 through year 5 |  | 11,100,000 |  |
Executive Retirement Program | PNM |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Actuarial gains (losses) recorded as regulatory assets and liabilities |  | 45,000 |  |
Expected disbursements by employer |  | 1,300,000 | 1,300,000 |
Executive Retirement Program | TNMP |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Actuarial gains (losses) recorded as regulatory assets and liabilities |  | 314,000 |  |
Expected disbursements by employer |  | $ 100,000 | $ 100,000 |
Non-US | Pension Plan | Equity Securities |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Investment allocation targets (as a percent) |  | 13.00% |  |

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