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Stockholders' Equity (Details) - USD ($)
 12 Months Ended
Dec. 30, 2024
Dec. 15, 2023
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Aug. 02, 2024
Aug. 01, 2024
Class of Stock [Line Items]              
Common stock, shares authorized (in shares)     200,000,000 120,000,000      
Payment of dividends     $ 775,000,000.0        
TXNM 2024 ATM Program              
Class of Stock [Line Items]              
Number of shares issued in transaction (in shares) 2,458,951            
Sale of stock, consideration received on transaction $ 800,000            
Payments of stock issuance costs $ 98,600,000            
Common stock subject to future settlement (in shares) 1,104,641            
TXNM 2022 ATM Program              
Class of Stock [Line Items]              
Number of shares issued in transaction (in shares)   4,365,510          
Sale of stock, consideration received on transaction $ 1,000,000            
Payments of stock issuance costs $ 198,200,000            
Common stock subject to future settlement (in shares) 0            
Line of Credit              
Class of Stock [Line Items]              
Debt-to-capital ratio (not more than) (as a percent)     70.00%        
PNM              
Class of Stock [Line Items]              
Common stock, shares authorized (in shares)     40,000,000 40,000,000      
Equity contribution from parent     $ 55,000,000 $ 0 $ 0    
Requirement to obtain approval to transfer more than a percentage of PNM's assets     5.00%        
Payment of dividends     $ 509,100,000        
Preferred stock, dividend rate (as a percent)     4.58%        
Preferred stock, redemption (as a percent)     102.00%        
Preferred stock outstanding (in shares)     115,293 115,293      
Preferred stock, cumulative shares authorized (in shares)     10,000,000 10,000,000      
PNM | Line of Credit              
Class of Stock [Line Items]              
Debt-to-capital ratio (not more than) (as a percent)     65.00%        
PNM | Affiliated Entity              
Class of Stock [Line Items]              
Cash dividends paid     $ 51,000,000 $ 0 153,500,000    
TNMP              
Class of Stock [Line Items]              
Common stock, shares authorized (in shares)     12,000,000 12,000,000      
Equity contribution from parent     $ 24,000,000 $ 40,900,000 68,000,000    
Payment of dividends     $ 318,000,000.0        
Preferred stock, cumulative shares authorized (in shares)     1,000,000        
TNMP | Line of Credit              
Class of Stock [Line Items]              
Debt-to-capital ratio (not more than) (as a percent)     65.00%        
TNMP | Affiliated Entity              
Class of Stock [Line Items]              
Cash dividends paid     $ 0 $ 0 $ 0    
PNMR and TNMP              
Class of Stock [Line Items]              
Preferred stock outstanding (in shares)     0        
TXNM              
Class of Stock [Line Items]              
Common stock, shares authorized (in shares)           200,000,000 120,000,000