Pension and Other Postretirement Benefit Plans - Schedule of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
PNM | Pension Plan
Components of Net Periodic Benefit Cost
Service cost	$ 0	$ 0
Interest cost	4,214	4,036
Expected return on plan assets	(7,141)	(7,133)
Amortization of net loss	3,949	4,541
Amortization of prior service cost	0	0
Net Periodic Benefit Cost (Income)	1,022	1,444
PNM | OPEB Plan
Components of Net Periodic Benefit Cost
Service cost	2	6
Interest cost	479	477
Expected return on plan assets	(1,088)	(1,042)
Amortization of net loss	0	0
Amortization of prior service cost	0	0
Net Periodic Benefit Cost (Income)	(607)	(559)
PNM | Executive Retirement Program
Components of Net Periodic Benefit Cost
Service cost	0	0
Interest cost	90	90
Expected return on plan assets	0	0
Amortization of net loss	82	100
Amortization of prior service cost	0	0
Net Periodic Benefit Cost (Income)	172	190
Texas-New Mexico Power Company | Pension Plan
Components of Net Periodic Benefit Cost
Service cost	0	0
Interest cost	430	435
Expected return on plan assets	(618)	(795)
Amortization of net loss	233	312
Amortization of prior service cost	0	0
Net Periodic Benefit Cost (Income)	45	(48)
Texas-New Mexico Power Company | OPEB Plan
Components of Net Periodic Benefit Cost
Service cost	9	11
Interest cost	77	77
Expected return on plan assets	(104)	(102)
Amortization of net loss	(130)	(80)
Amortization of prior service cost	0	0
Net Periodic Benefit Cost (Income)	(148)	(94)
Texas-New Mexico Power Company | Executive Retirement Program
Components of Net Periodic Benefit Cost
Service cost	0	0
Interest cost	3	4
Expected return on plan assets	0	0
Amortization of net loss	0	9
Amortization of prior service cost	0	0
Net Periodic Benefit Cost (Income)	$ 3	$ 13