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Pension and Other Postretirement Benefits - Actuarial (Gain) Loss Results (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
PNM | Pension Plan    
Defined Benefit Plan Disclosure [Line Items]    
Discount rates $ 8,806 $ (111,478)
Claims, contributions, and demographic experience (1,777) (7,074)
Mortality rate (2,739) 0
Other assumptions and experience 0 0
Actuarial (gain) loss 4,290 (118,552)
PNM | Other Postretirement Benefits    
Defined Benefit Plan Disclosure [Line Items]    
Discount rates 868 (11,876)
Claims, contributions, and demographic experience (2,171) (2,985)
Assumed participation rate 0 0
Mortality rate (305) 0
Dental trend assumption 0 32
Actuarial (gain) loss (1,608) (14,829)
TNMP | Pension Plan    
Defined Benefit Plan Disclosure [Line Items]    
Discount rates 969 (11,697)
Claims, contributions, and demographic experience 538 (742)
Mortality rate (239) 0
Other assumptions and experience (7) 728
Actuarial (gain) loss 1,261 (11,711)
TNMP | Other Postretirement Benefits    
Defined Benefit Plan Disclosure [Line Items]    
Discount rates 174 (2,469)
Claims, contributions, and demographic experience (423) (319)
Assumed participation rate 0 0
Mortality rate (33) 0
Dental trend assumption 0 0
Actuarial (gain) loss $ (282) $ (2,788)