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Summary of the Business and Significant Accounting Policies - Narrative (Details)
 12 Months Ended
Dec. 31, 2024
USD ($)
utility
shares
Dec. 31, 2023
USD ($)
shares
Dec. 31, 2022
USD ($)
Aug. 02, 2024
shares
Aug. 01, 2024
shares
Accounting Policies Disclosures [Line Items]          
Common stock, shares authorized (in shares) | shares 200,000,000 120,000,000      
Payment defaults $ 0        
Net gains (losses) on debt securities $ 8,639,000 $ 4,008,000 $ (33,392,000)    
TXNM          
Accounting Policies Disclosures [Line Items]          
Number of regulated utilities | utility 2        
Common stock, shares authorized (in shares) | shares       200,000,000 120,000,000
Restricted cash     0    
PNM          
Accounting Policies Disclosures [Line Items]          
Common stock, shares authorized (in shares) | shares 40,000,000 40,000,000      
Restricted cash     0    
Allowance for funds used during construction, capitalized interest $ 12,900,000 $ 9,500,000 $ 3,700,000    
Allowance for funds used during construction, capitalized interest rate (as a percent) 3.19% 2.99% 1.70%    
Allowance for equity funds used during construction $ 13,000,000.0 $ 9,800,000 $ 9,300,000    
Allowance for funds used during construction, capitalized cost of equity rate (as a percent) 3.30% 3.24% 4.26%    
Net gains (losses) on debt securities $ 17,800,000 $ (19,100,000) $ 25,800,000    
TNMP          
Accounting Policies Disclosures [Line Items]          
Common stock, shares authorized (in shares) | shares 12,000,000 12,000,000      
Restricted cash $ 0 $ 0 0    
Allowance for funds used during construction, capitalized interest $ 8,000,000 $ 5,700,000 $ 3,400,000    
Allowance for funds used during construction, capitalized interest rate (as a percent) 4.14% 3.49% 2.25%    
Allowance for equity funds used during construction $ 4,800,000 $ 5,100,000 $ 4,500,000    
Allowance for funds used during construction, capitalized cost of equity rate (as a percent) 2.48% 3.17% 2.99%