Pension and Other Postretirement Benefits - APBO, PBO, Fair Value of Plan Assets, and Funded Status of the Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Accrued pension liability and postretirement benefit cost	$ 21,429	$ 32,799
PNM
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Accrued pension liability and postretirement benefit cost	19,949	32,007
PNM | Pension Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balance at beginning of year	433,645	584,061
Service cost	0	0	$ 0
Interest cost	23,653	16,857	16,143
Actuarial (gain) loss	4,290	(118,552)
Benefits paid	(42,931)	(48,721)
Settlements	0	0
Balance at end of year	418,657	433,645	584,061
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	410,463	576,707
Actual return on plan assets	39,679	(117,523)
Employer contributions	0	0
Benefits paid	(42,931)	(48,721)
Settlements	0	0
Fair value of plan assets at end of year	407,211	410,463	576,707
Funded status – asset (liability) for pension benefits	(11,446)	(23,182)
PNM | Other Postretirement Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balance at beginning of year	49,950	66,984
Service cost	0	10	23
Interest cost	2,703	1,914	1,907
Participant contributions	1,592	1,431
Actuarial (gain) loss	(1,608)	(14,829)
Benefits paid	(6,420)	(6,396)
Curtailment loss	0	836	0
Balance at end of year	46,217	49,950	66,984
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	70,301	95,805
Actual return on plan assets	7,762	(23,156)
Employer contributions	157	2,617
Participant contributions	1,592	1,431
Benefits paid	(6,420)	(6,396)
Fair value of plan assets at end of year	73,392	70,301	95,805
Funded status – asset (liability) for pension benefits	27,175	20,351
PNM | Executive Retirement Program
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balance at beginning of year	10,042	12,612
Service cost	0	0	0
Interest cost	540	362	363
Actuarial (gain) loss	411	(1,628)
Benefits paid	(1,279)	(1,304)
Balance at end of year	9,714	10,042	12,612
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Less current liability	1,210	1,217
Accrued pension liability and postretirement benefit cost	8,504	8,825
TNMP
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Accrued pension liability and postretirement benefit cost	1,480	792
TNMP | Pension Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balance at beginning of year	43,961	59,609
Service cost	0	0	0
Interest cost	2,402	1,720	1,741
Actuarial (gain) loss	1,261	(11,711)
Benefits paid	(5,042)	(3,403)
Settlements	0	(2,254)
Balance at end of year	42,582	43,961	59,609
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	43,447	62,942
Actual return on plan assets	2,948	(13,838)
Employer contributions	0	0
Benefits paid	(5,042)	(3,403)
Settlements	0	(2,254)
Fair value of plan assets at end of year	41,353	43,447	62,942
Funded status – asset (liability) for pension benefits	(1,229)	(514)
TNMP | Other Postretirement Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balance at beginning of year	7,705	10,570
Service cost	21	38	45
Interest cost	425	307	308
Participant contributions	359	219
Actuarial (gain) loss	(282)	(2,788)
Benefits paid	(897)	(641)
Curtailment loss	0	0
Balance at end of year	7,331	7,705	10,570
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	8,718	12,593
Actual return on plan assets	173	(3,453)
Employer contributions	0	0
Participant contributions	359	219
Benefits paid	(897)	(641)
Fair value of plan assets at end of year	8,353	8,718	12,593
Funded status – asset (liability) for pension benefits	1,022	1,013
TNMP | Executive Retirement Program
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balance at beginning of year	344	406
Service cost	0	0	0
Interest cost	18	11	17
Actuarial (gain) loss	13	(2)
Benefits paid	(59)	(71)
Balance at end of year	316	344	$ 406
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Less current liability	64	66
Accrued pension liability and postretirement benefit cost	$ 252	$ 278