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Pension and Other Postretirement Benefits - Narrative (Details) - USD ($)
 12 Months Ended
Jan. 01, 2018
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Expected return on plan assets   4.00%    
Amortization of gains and losses that are outside the corridor   5 years    
Maximum annual contributions per employee   75.00%    
Employer matching contribution, percent of employees' gross pay   6.00%    
Minimum        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Non-matching contribution of eligible compensation based on eligible employee's age   3.00%    
Maximum        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Non-matching contribution of eligible compensation based on eligible employee's age   10.00%    
PNM        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Rate of return   10.20%    
TNMP        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Rate of return   7.22%    
Pension Plan        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Expected long-term return resulting from effect of 1% change   1.00%    
Expected long-term return resulting from effect of one-percentage point increase   1.00%    
Expected future employer contributions, year two through four   $ 0    
Expected future employer contributions, after year four   $ 200,000    
Weighted average discount rate related to anticipated contributions   5.47%    
Pension Plan | Equity Securities        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Investment allocation targets   35.00%    
Pension Plan | Fixed income        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Investment allocation targets   50.00%    
Pension Plan | Alternative Investments        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Investment allocation targets   15.00%    
Pension Plan | PNM        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Expected return on plan assets   6.30% 5.50% 5.50%
Expected long-term return on assets decrease resulting in increase net periodic costs In next fiscal year   $ 4,500,000    
Actuarial gains (losses) recorded as regulatory assets and liabilities   6,193,000    
Employer contributions   $ 0 $ 0  
Pension Plan | TNMP        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Expected return on plan assets   5.50% 4.40% 5.50%
Expected long-term return on assets decrease resulting in increase net periodic costs In next fiscal year   $ 500,000    
Actuarial gains (losses) recorded as regulatory assets and liabilities   (1,005,000)    
Employer contributions   $ 0 $ 0  
Pension Plan | TNMP | Equity Securities        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Investment allocation targets   16.00%    
Pension Plan | TNMP | Fixed income        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Investment allocation targets   70.00%    
Pension Plan | TNMP | Alternative Investments        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Investment allocation targets   14.00%    
Other Postretirement Benefits        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Expected long-term return resulting from effect of 1% change   1.00%    
Other Postretirement Benefits | Equity Securities        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Investment allocation targets   30.00%    
Other Postretirement Benefits | Fixed income        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Investment allocation targets   70.00%    
Other Postretirement Benefits | PNM        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Expected return on plan assets   5.90% 4.75% 4.75%
Expected long-term return on assets decrease resulting in increase net periodic costs In next fiscal year   $ 800,000    
Rate of return   11.40%    
Actuarial gains (losses) recorded as regulatory assets and liabilities   $ (4,400,000)    
Employer matching contribution, maximum 5.00%      
Employer contributions   $ 157,000 $ 2,617,000  
Other Postretirement Benefits | TNMP        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Expected return on plan assets   4.70% 3.80% 3.80%
Expected long-term return on assets decrease resulting in increase net periodic costs In next fiscal year   $ 100,000    
Rate of return   2.00%    
Actuarial gains (losses) recorded as regulatory assets and liabilities   $ (100,000)    
Effect of 1%-point change in assumed health care cost trend rates on net periodic expense and APBO   0    
Employer contributions   0 $ 0  
Other Postretirement Benefits | PNM and TNMP        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Employer contributions   0 0  
Expected employer contributions in fiscal year through year 5   0 0  
Expected employer disbursements for next fiscal year   200,000    
Expected employer disbursements by employer in year 2 through year 5   10,100,000    
Executive Retirement Program | PNM        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Actuarial gains (losses) recorded as regulatory assets and liabilities   (411,000)    
Expected disbursements by employer   1,300,000 1,300,000  
Executive Retirement Program | TNMP        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Actuarial gains (losses) recorded as regulatory assets and liabilities   (13,000)    
Expected disbursements by employer   $ 100,000 $ 100,000  
Non-US | Pension Plan | Equity Securities        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Investment allocation targets   13.00%