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Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Income) Recognized (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
PNM | Pension Plan      
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]      
Service cost $ 0 $ 0 $ 0
Interest cost 23,653 16,857 16,143
Expected return on plan assets (29,196) (28,563) (28,531)
Amortization of net loss 10,583 15,794 18,166
Amortization of prior service cost 0 0 0
Net periodic benefit cost 5,040 4,088 5,778
PNM | Other Postretirement Benefits      
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]      
Service cost 0 10 23
Interest cost 2,703 1,914 1,907
Expected return on plan assets (4,969) (4,351) (4,167)
Amortization of net loss 0 0 0
Curtailment loss 0 836 0
Net periodic benefit cost (2,266) (1,591) (2,237)
PNM | Executive Retirement Program      
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]      
Service cost 0 0 0
Interest cost 540 362 363
Amortization of net loss 152 327 395
Amortization of prior service cost 0 0 0
Net periodic benefit cost 692 689 758
TNMP | Pension Plan      
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]      
Service cost 0 0 0
Interest cost 2,402 1,720 1,741
Expected return on plan assets (2,697) (2,472) (3,181)
Amortization of net loss 439 932 1,247
Amortization of prior service cost 0 0 0
Settlement loss 0 1,033 746
Net periodic benefit cost 144 1,213 553
TNMP | Other Postretirement Benefits      
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]      
Service cost 21 38 45
Interest cost 425 307 308
Expected return on plan assets (481) (418) (407)
Amortization of net loss (760) (520) (322)
Curtailment loss 0 0  
Net periodic benefit cost (795) (593) (376)
TNMP | Executive Retirement Program      
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]      
Service cost 0 0 0
Interest cost 18 11 17
Amortization of net loss 0 0 33
Amortization of prior service cost 0 0 0
Net periodic benefit cost $ 18 $ 11 $ 50