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Income Taxes (Details) - USD ($)
$ in Millions
 6 Months Ended 12 Months Ended
Jun. 30, 2024
Dec. 31, 2017
Income Tax Contingency [Line Items]    
Effective tax rate 15.29%  
Regulatory disallowances, tax effect $ 1.1  
Sale of equity method investee, tax effect 19.5  
Income tax assessment 0.1  
Deferred federal, state and local, income taxes $ 23.3  
NMPRC    
Income Tax Contingency [Line Items]    
Period of time for proposed return to customers the benefit of the reduction in federal corporate income tax rate 5 years 23 years
Unprotected excess deferred income taxes $ 62.7  
PNM    
Income Tax Contingency [Line Items]    
Effective tax rate 14.31%  
Income tax assessment $ 0.1  
Deferred federal, state and local, income taxes $ 20.7  
TNMP    
Income Tax Contingency [Line Items]    
Effective tax rate 20.71%  
Income tax assessment $ 0.1  
Deferred federal, state and local, income taxes $ 2.6