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Fair Value of Derivative and Other Financial Instruments - Schedule of Items Recorded and Presented by Level of Hierarchy (Details) - USD ($)
$ in Thousands
 9 Months Ended 12 Months Ended
Sep. 30, 2025
Dec. 31, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment securities $ 493,895 $ 475,524
Fair value of long-term debt 5,172,203 4,706,076
Carrying Amount    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of long-term debt 5,082,676 4,923,368
PNM    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale debt securities 44,804  
Investment securities 493,895 475,524
Fair value of long-term debt 2,847,861 2,284,362
PNM | Carrying Amount    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of long-term debt 2,941,491 2,459,592
TNMP    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of long-term debt 1,606,015 1,324,194
TNMP | Carrying Amount    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of long-term debt 1,602,738 1,464,079
Recurring | PNM    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale debt securities 430,292 453,421
Investment securities 493,895 475,524
Unrealized Gains 358 324
Recurring | PNM | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale debt securities 422,581 446,225
Recurring | PNM | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale debt securities 7,711 7,196
Recurring | PNM | Cash and cash equivalents    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents 29,361 150,745
Recurring | PNM | Cash and cash equivalents | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents 29,361 150,745
Recurring | PNM | Cash and cash equivalents | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents 0 0
Recurring | PNM | Corporate stocks, common    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity securities: 156,079 134,553
Recurring | PNM | Corporate stocks, common | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity securities: 156,079 134,553
Recurring | PNM | Corporate stocks, common | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity securities: 0 0
Recurring | PNM | Mutual funds and other    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity securities: 200,048 135,779
Recurring | PNM | Mutual funds and other | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity securities: 200,048 135,779
Recurring | PNM | Mutual funds and other | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity securities: 0 0
Recurring | PNM | U.S. government    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale debt securities 37,093 25,148
Unrealized Gains 274 202
Recurring | PNM | U.S. government | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale debt securities 37,093 25,148
Recurring | PNM | U.S. government | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale debt securities 0 0
Recurring | PNM | Corporate and other    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale debt securities 7,711 7,196
Unrealized Gains 84 122
Recurring | PNM | Corporate and other | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale debt securities 0 0
Recurring | PNM | Corporate and other | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale debt securities 7,711 7,196
Recurring | PNM | Uncategorized collective investment trust    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Other investments 44,635 $ 22,103
Recurring | PNM | Uncategorized real estate fund    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Other investments $ 18,968