Summary of the Business and Significant Accounting Policies - Narrative (Details)	12 Months Ended
	Dec. 31, 2021 USD ($) utility	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Accounting Policies Disclosures [Line Items]
Payment defaults	$ 0
Allowance for equity funds used during construction	$ 13,217,000	$ 11,254,000	$ 9,478,000
PNMR
Accounting Policies Disclosures [Line Items]
Number of regulated utilities | utility	2
Restricted cash	$ 0	0
Public Service Company of New Mexico
Accounting Policies Disclosures [Line Items]
Restricted cash	0	0
Allowance for funds used during construction, capitalized interest	$ 3,400,000	$ 3,000,000	$ 5,000,000
Allowance for funds used during construction, capitalized interest rate	1.70%	2.40%	2.99%
Allowance for equity funds used during construction	$ 9,905,000	$ 6,958,000	$ 6,656,000
Allowance for funds used during construction, capitalized cost of equity rate	4.94%	3.42%	3.95%
Impairment losses on securities held in the NDT	$ (700,000)	$ 3,200,000	$ 5,700,000
Texas-New Mexico Power Company
Accounting Policies Disclosures [Line Items]
Restricted cash	0	0
Allowance for funds used during construction, capitalized interest	$ 1,600,000	$ 2,100,000	$ 2,400,000
Allowance for funds used during construction, capitalized interest rate	1.80%	2.20%	3.23%
Allowance for equity funds used during construction	$ 3,300,000	$ 4,300,000	$ 2,800,000
Allowance for funds used during construction, capitalized cost of equity rate	3.67%	4.42%	3.78%