Pension and Other Postretirement Benefit Plans - Schedule of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
PNM | Pension Plan
Components of Net Periodic Benefit Cost
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	4,214	4,035	8,428	8,071
Expected return on plan assets	(7,141)	(7,132)	(14,282)	(14,265)
Amortization of net loss	3,949	4,542	7,898	9,083
Amortization of prior service cost	0	0	0	0
Net Periodic Benefit Cost (Income)	1,022	1,445	2,044	2,889
PNM | OPEB Plan
Components of Net Periodic Benefit Cost
Service cost	2	7	4	13
Interest cost	479	477	958	954
Expected return on plan assets	(1,088)	(1,041)	(2,176)	(2,083)
Amortization of net loss	0	0	0	0
Amortization of prior service cost	0	0	0	0
Net Periodic Benefit Cost (Income)	(607)	(557)	(1,214)	(1,116)
PNM | Executive Retirement Program
Components of Net Periodic Benefit Cost
Service cost	0	0	0	0
Interest cost	90	91	180	181
Expected return on plan assets	0	0	0	0
Amortization of net loss	82	97	164	197
Amortization of prior service cost	0	0	0	0
Net Periodic Benefit Cost (Income)	172	188	344	378
Texas-New Mexico Power Company | Pension Plan
Components of Net Periodic Benefit Cost
Service cost	0	0	0	0
Interest cost	430	436	860	871
Expected return on plan assets	(618)	(796)	(1,236)	(1,591)
Amortization of net loss	233	312	466	624
Amortization of prior service cost	0	0	0	0
Net Periodic Benefit Cost (Income)	45	(48)	90	(96)
Texas-New Mexico Power Company | OPEB Plan
Components of Net Periodic Benefit Cost
Service cost	9	11	18	22
Interest cost	77	77	154	154
Expected return on plan assets	(104)	(101)	(208)	(203)
Amortization of net loss	(130)	(81)	(260)	(161)
Amortization of prior service cost	0	0	0	0
Net Periodic Benefit Cost (Income)	(148)	(94)	(296)	(188)
Texas-New Mexico Power Company | Executive Retirement Program
Components of Net Periodic Benefit Cost
Service cost	0	0	0	0
Interest cost	3	5	6	9
Expected return on plan assets	0	0	0	0
Amortization of net loss	0	8	0	17
Amortization of prior service cost	0	0	0	0
Net Periodic Benefit Cost (Income)	$ 3	$ 13	$ 6	$ 26