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Pension and Other Postretirement Benefit Plans - Narrative (Details) - USD ($)
 3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Pension Plan | PNM    
Defined Benefit Plan Disclosure [Line Items]    
Contributions by employer $ 0 $ 0
Estimated employer contributions for remainder of fiscal year through year four $ 0  
Pension Plan | PNM | Maximum    
Defined Benefit Plan Disclosure [Line Items]    
Assumptions used calculating net periodic benefit cost, discount rate 5.50%  
Pension Plan | Texas-New Mexico Power Company    
Defined Benefit Plan Disclosure [Line Items]    
Contributions by employer $ 0 0
Estimated employer contributions for remainder of fiscal year through year four 0  
Estimated future contributions, year five $ 200,000  
Pension Plan | Texas-New Mexico Power Company | Maximum    
Defined Benefit Plan Disclosure [Line Items]    
Assumptions used calculating net periodic benefit cost, discount rate 5.50%  
OPEB Plan | PNM    
Defined Benefit Plan Disclosure [Line Items]    
Contributions by employer $ 0 0
Disbursements by employer 100,000 800,000
Disbursements by employer, year one through four 10,100,000  
Estimated disbursement by employer, current year 200,000  
OPEB Plan | Texas-New Mexico Power Company    
Defined Benefit Plan Disclosure [Line Items]    
Contributions by employer 0 0
Disbursements by employer, year one through four 0  
Executive Retirement Program | PNM    
Defined Benefit Plan Disclosure [Line Items]    
Contributions by employer 300,000 100,000
Disbursements by employer, year one through four 4,400,000  
Estimated disbursement by employer, current year 1,200,000  
Executive Retirement Program | Texas-New Mexico Power Company    
Defined Benefit Plan Disclosure [Line Items]    
Disbursements by employer, year one through four 200,000  
Estimated disbursement by employer, current year 100,000  
Executive Retirement Program | Texas-New Mexico Power Company | Maximum    
Defined Benefit Plan Disclosure [Line Items]    
Contributions by employer $ 100,000 $ 100,000