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Stockholders' Equity (Details) - USD ($)
 12 Months Ended
Dec. 15, 2020
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Class of Stock [Line Items]        
Payment of dividends   $ 321,900,000    
PNMR 2020 Forward Equity Sales Agreement        
Class of Stock [Line Items]        
Number of shares issued in transaction (in shares) 4,400,000      
Sale of stock, consideration received on transaction $ 198,200,000      
Payments of stock issuance costs $ 1,000,000      
Line of Credit        
Class of Stock [Line Items]        
Debt-to-capital ratio (not more than)   70.00%    
PNM        
Class of Stock [Line Items]        
Equity contribution from parent   $ 0 $ 0 $ 53,000,000
Requirement to obtain approval to transfer more than a percentage of PNM's assets   5.00%    
Preferred stock, dividend rate   4.58%    
Preferred stock, redemption 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)   65.00%    
PNM | Affiliated Entity        
Class of Stock [Line Items]        
Cash dividends paid to parent company by consolidated subsidiaries     $ 153,500,000 60,000,000
TNMP        
Class of Stock [Line Items]        
Equity contribution from parent   $ 40,900,000 $ 68,000,000 $ 52,000,000
Payment of dividends   $ 339,500,000    
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)   65.00%    
PNMR and TNMP        
Class of Stock [Line Items]        
Preferred stock outstanding (in shares)   0