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Commitments and Contingencies - Coal Supply (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended 12 Months Ended
Mar. 31, 2024
Jun. 30, 2025
Jun. 30, 2024
Dec. 31, 2024
Jan. 31, 2016
Public Service Company of New Mexico | Four Corners CSA          
Public Utilities, Commitments And Contingencies [Line Items]          
Funds contributed, mine reclamation trust   $ 3.2      
Reclamation trust funding, 2025   0.5      
San Juan Generating Station | Coal supply          
Public Utilities, Commitments And Contingencies [Line Items]          
Cash used to support bank letter or credit arrangement         $ 30.3
San Juan Generating Station | Coal supply | NM Capital          
Public Utilities, Commitments And Contingencies [Line Items]          
Requirement to post reclamation bonds   118.7      
Cash used to support bank letter or credit arrangement   30.3      
Underground | Public Service Company of New Mexico | Loss on long-term purchase commitment          
Public Utilities, Commitments And Contingencies [Line Items]          
Loss contingency accrual   54.1   $ 52.9  
Underground | San Juan Generating Station | Public Service Company of New Mexico | Loss on long-term purchase commitment          
Public Utilities, Commitments And Contingencies [Line Items]          
Estimate of possible loss   62.7      
Surface | Public Service Company of New Mexico | Loss on long-term purchase commitment          
Public Utilities, Commitments And Contingencies [Line Items]          
Loss contingency accrual   29.6   38.3  
Surface | San Juan Generating Station | Public Service Company of New Mexico | Loss on long-term purchase commitment          
Public Utilities, Commitments And Contingencies [Line Items]          
Estimate of possible loss   41.1      
San Juan Generating Station          
Public Utilities, Commitments And Contingencies [Line Items]          
Reclamation costs $ 20.9        
Regulatory disallowance     $ 4.0    
Regulatory disallowance related to other costs     0.5    
San Juan Generating Station | Public Service Company of New Mexico | Loss on long-term purchase commitment          
Public Utilities, Commitments And Contingencies [Line Items]          
Annual funding post-term reclamation trust       27.3  
Annual funding post-term reclamation trust, remainder of year   1.6      
Annual funding post-term reclamation trust, year one   1.0      
Annual funding post-term reclamation trust, year two   0.4      
San Juan Generating Station | Underground          
Public Utilities, Commitments And Contingencies [Line Items]          
Increase in regulatory liabilities $ 17.0        
San Juan Generating Station | Surface          
Public Utilities, Commitments And Contingencies [Line Items]          
Reclamation costs       1.6  
Reclamation, maximum collection from customers     $ 100.0 $ 100.0  
San Juan Generating Station and Four Corners | Public Service Company of New Mexico | Mine Reclamation Trust          
Public Utilities, Commitments And Contingencies [Line Items]          
Customer reclamation funding cost   $ 100.0