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Commitments and Contingencies - Coal Supply (Details) - USD ($)
 3 Months Ended 6 Months Ended 12 Months Ended
Mar. 31, 2023
Jun. 30, 2022
Dec. 31, 2022
Jan. 31, 2016
PNM | Loss on long-term purchase commitment | Surface        
Public Utilities, Commitments And Contingencies [Line Items]        
Loss contingency accrual $ 59,800,000   $ 62,600,000  
PNM | Loss on long-term purchase commitment | Underground        
Public Utilities, Commitments And Contingencies [Line Items]        
Loss contingency accrual 28,400,000   28,200,000  
PNM | Loss on long-term purchase commitment | San Juan Generating Station | Surface        
Public Utilities, Commitments And Contingencies [Line Items]        
Estimate of possible loss 64,500,000      
PNM | Loss on long-term purchase commitment | San Juan Generating Station | Underground        
Public Utilities, Commitments And Contingencies [Line Items]        
Estimate of possible loss 33,300,000      
Coal supply | San Juan Generating Station        
Public Utilities, Commitments And Contingencies [Line Items]        
Cash used to support bank letter or credit arrangement       $ 30,300,000
Coal supply | Four Corners        
Public Utilities, Commitments And Contingencies [Line Items]        
Payments for relief from obligations 75,000,000      
Coal supply | NM Capital | San Juan Generating Station        
Public Utilities, Commitments And Contingencies [Line Items]        
Requirement to post reclamation bonds 118,700,000      
Cash used to support bank letter or credit arrangement 30,300,000      
Four Corners CSA | PNM        
Public Utilities, Commitments And Contingencies [Line Items]        
Funds contributed, mine reclamation trust     $ 2,400,000  
Reclamation trust funding, remainder of year 2,100,000      
Reclamation trust funding, year one 2,100,000      
Reclamation trust funding, year two 2,100,000      
San Juan Generating Station | Loss on long-term purchase commitment | PNM        
Public Utilities, Commitments And Contingencies [Line Items]        
Annual funding post-term reclamation trust   $ 10,000,000    
Annual funding post-term reclamation trust, remainder of year 0      
Annual funding post-term reclamation trust, year one 0      
Annual funding post-term reclamation trust, year two 0      
San Juan Generating Station and Four Corners | Mine Reclamation Trust | PNM        
Public Utilities, Commitments And Contingencies [Line Items]        
Customer reclamation funding cost $ 100,000,000