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Pension and Other Postretirement Benefit Plans - Schedule of Net Periodic Benefit Costs (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2023
Sep. 30, 2022
Sep. 30, 2023
Sep. 30, 2022
PNM | Pension Plan        
Components of Net Periodic Benefit Cost        
Service cost $ 0 $ 0 $ 0 $ 0
Interest cost 5,913 4,215 17,740 12,643
Expected return on plan assets (7,299) (7,140) (21,897) (21,422)
Amortization of net loss 2,646 3,948 7,937 11,846
Amortization of prior service cost 0 0 0 0
Net Periodic Benefit Cost (Income) 1,260 1,023 3,780 3,067
PNM | OPEB Plan        
Components of Net Periodic Benefit Cost        
Service cost 0 2 0 6
Interest cost 675 479 2,027 1,437
Expected return on plan assets (1,242) (1,088) (3,727) (3,264)
Amortization of net loss 0 0 0 0
Amortization of prior service cost 0 0 0 0
Net Periodic Benefit Cost (Income) (567) (607) (1,700) (1,821)
PNM | Executive Retirement Program        
Components of Net Periodic Benefit Cost        
Service cost 0 0 0 0
Interest cost 135 90 405 270
Expected return on plan assets 0 0 0 0
Amortization of net loss 38 81 114 245
Amortization of prior service cost 0 0 0 0
Net Periodic Benefit Cost (Income) 173 171 519 515
Texas-New Mexico Power Company | Pension Plan        
Components of Net Periodic Benefit Cost        
Service cost 0 0 0 0
Interest cost 601 430 1,802 1,290
Expected return on plan assets (674) (618) (2,023) (1,854)
Amortization of net loss 110 233 329 699
Amortization of prior service cost 0 0 0 0
Net Periodic Benefit Cost (Income) 37 45 108 135
Texas-New Mexico Power Company | OPEB Plan        
Components of Net Periodic Benefit Cost        
Service cost 5 9 16 27
Interest cost 106 77 319 231
Expected return on plan assets (120) (104) (361) (312)
Amortization of net loss (190) (130) (570) (390)
Amortization of prior service cost 0 0 0 0
Net Periodic Benefit Cost (Income) (199) (148) (596) (444)
Texas-New Mexico Power Company | Executive Retirement Program        
Components of Net Periodic Benefit Cost        
Service cost 0 0 0 0
Interest cost 3 2 9 8
Expected return on plan assets 0 0 0 0
Amortization of net loss 0 0 0 0
Amortization of prior service cost 0 0 0 0
Net Periodic Benefit Cost (Income) $ 3 $ 2 $ 9 $ 8