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Significant Accounting Policies and Responsibility for Financial Statements (Details) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2024
Jun. 30, 2024
Sep. 30, 2023
Jun. 30, 2023
Sep. 30, 2024
Sep. 30, 2023
Aug. 02, 2024
Aug. 01, 2024
Dec. 31, 2023
Dividends Payable [Line Items]                  
Common stock, shares authorized (in shares) 200,000,000       200,000,000       120,000,000
Payment defaults under agreements $ 0       $ 0        
Dividends declared per common share (in dollars per share) $ 0.3875 $ 0.3875 $ 0.3675 $ 0.3675 $ 1.1625 $ 1.1025      
Dividends declared on common stock $ 69,906,000   $ 63,088,000   $ 104,858,000 $ 94,634,000      
TXNM                  
Dividends Payable [Line Items]                  
Common stock, shares authorized (in shares)             200,000,000 120,000,000  
Equity contribution from parent $ 0   0   $ 0 0      
Public Service Company of New Mexico                  
Dividends Payable [Line Items]                  
Common stock, shares authorized (in shares) 40,000,000       40,000,000       40,000,000
Equity contribution from parent $ 0       $ 55,000,000 0      
Dividends declared on common stock $ 0   0   $ 0 0      
Texas-New Mexico Power Company                  
Dividends Payable [Line Items]                  
Common stock, shares authorized (in shares) 12,000,000       12,000,000       12,000,000
Dividends declared on common stock $ 0   $ 0   $ 0 $ 0