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Pension and Other Postretirement Benefits - Schedule of Weighted-Average Assumptions of PBO, APBO and Executive Retirement Programs (Details)
12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]      
Expected return on plan assets 4.00%    
PNM | Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate for determining 5.78% 5.46% 5.74%
Discount rate for determining net periodic benefit cost 5.46% 5.74% 3.00%
Expected return on plan assets 6.86% 6.30% 5.50%
PNM | Other Postretirement Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate for determining 5.78% 5.48% 5.75%
Discount rate for determining net periodic benefit cost 5.48% 5.75% 2.99%
Expected return on plan assets 6.60% 5.90% 4.75%
PNM | Executive Retirement Program      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate for determining 5.78% 5.45% 5.73%
Discount rate for determining net periodic benefit cost 5.45% 5.73% 3.02%
TNMP | Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate for determining 5.78% 5.47% 5.75%
Discount rate for determining net periodic benefit cost 5.47% 5.75% 3.01%
Expected return on plan assets 5.95% 5.50% 4.40%
TNMP | Other Postretirement Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate for determining 5.78% 5.48% 5.75%
Discount rate for determining net periodic benefit cost 5.48% 5.75% 2.99%
Expected return on plan assets 5.25% 4.70% 3.80%
TNMP | Executive Retirement Program      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate for determining   5.47% 5.75%
Discount rate for determining net periodic benefit cost 5.47% 5.75% 3.01%