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Summary of the Business and Significant Accounting Policies - Narrative (Details)
 12 Months Ended
Dec. 31, 2023
USD ($)
utility
Dec. 31, 2022
USD ($)
Dec. 31, 2021
USD ($)
Accounting Policies Disclosures [Line Items]      
Payment defaults $ 0    
Net gains (losses) on debt securities $ 4,008,000 $ (33,392,000) $ 8,554,000
PNMR      
Accounting Policies Disclosures [Line Items]      
Number of regulated utilities | utility 2    
Restricted cash $ 0 0  
PNM      
Accounting Policies Disclosures [Line Items]      
Restricted cash 0 0  
Allowance for funds used during construction, capitalized interest $ 9,500,000 $ 3,700,000 $ 3,400,000
Allowance for funds used during construction, capitalized interest rate 2.99% 1.70% 1.70%
Allowance for equity funds used during construction $ 9,800,000 $ 9,300,000 $ 9,900,000
Allowance for funds used during construction, capitalized cost of equity rate 3.24% 4.26% 4.94%
Net gains (losses) on debt securities $ (19,100,000) $ 25,800,000 $ (700,000)
TNMP      
Accounting Policies Disclosures [Line Items]      
Restricted cash 0 0  
Allowance for funds used during construction, capitalized interest $ 5,700,000 $ 3,400,000 $ 1,600,000
Allowance for funds used during construction, capitalized interest rate 3.49% 2.25% 1.80%
Allowance for equity funds used during construction $ 5,100,000 $ 4,500,000 $ 3,300,000
Allowance for funds used during construction, capitalized cost of equity rate 3.17% 2.99% 3.67%