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Financing - Long-term Debt (Details) - USD ($) | Jun. 22, 2020 | Mar. 09, 2018 | Dec. 31, 2020 | Dec. 22, 2020 | Dec. 21, 2020 | Jun. 30, 2020 | Dec. 31, 2019 | Dec. 18, 2019 | Jan. 18, 2019 | Dec. 21, 2018
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Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Total |  |  | $ 3,294,043,000 |  |  |  | $ 3,004,043,000 |  |  |
Principal, less current maturities |  |  | 576,000,000 |  |  |  | 490,345,000 |  |  |
Long-term debt, excluding current maturities, gross |  |  | 2,718,043,000 |  |  |  | 2,513,698,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | (1,107,000) |  |  |  | (3,674,000) |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net, Less current maturities |  |  | 482,000 |  |  |  | 77,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net, excluding current maturities |  |  | (1,589,000) |  |  |  | (3,751,000) |  |  |
PNMR 2018 Two-Year Term Loan due December 2020 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  | $ 50,000,000.0
Term loans |  |  |  |  | $ 50,000,000.0 |  |  |  |  |
PNMR 2020 Term Loan due January 2022 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Term loans |  |  |  |  | $ 150,000,000.0 |  |  |  |  |
PNMR 2020 Delayed-Draw Term Loan due January 2022 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Term loans |  |  | $ 80,000,000.0 | $ 300,000,000.0 |  |  |  |  |  |
Bonds |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Repayments of debt | $ 302,500,000 |  |  |  |  |  |  |  |  |
Bonds | Pollution Control Revenue Bonds |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  | $ 100,300,000 |  |  |  |
Term loans |  |  |  |  |  |  | 100,300,000 |  |  |
Stated percentage |  |  | 0.19% |  |  |  |  |  |  |
Senior Unsecured Notes: | PNMR 3.25% 2018 SUNs due March 2021 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  | $ 300,000,000.0 |  |  |  |  |  |  |  |
Term loans |  | $ 220,000,000.0 |  |  |  |  |  |  |  |
Stated percentage |  | 3.25% |  |  |  |  |  |  |  |
Public Service Company of New Mexico |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Total |  |  | $ 1,705,845,000 |  |  |  | 1,755,845,000 |  |  |
Principal, less current maturities |  |  | 346,000,000 |  |  |  | 350,345,000 |  |  |
Long-term debt, excluding current maturities, gross |  |  | 1,359,845,000 |  |  |  | 1,405,500,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | 9,225,000 |  |  |  | 7,825,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net, Less current maturities |  |  | 430,000 |  |  |  | 77,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net, excluding current maturities |  |  | $ 8,795,000 |  |  |  | 7,748,000 |  |  |
Public Service Company of New Mexico | PNM 2019 $250.0 Million Term Loan due July 2020 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  | $ 250,000,000.0 |
Public Service Company of New Mexico | PNM 2019 $40.0 Million Term Loan due June 2021 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  | $ 40,000,000.0 |  |
Public Service Company of New Mexico | Senior Unsecured Notes, Pollution Control Revenue Bonds: | 1.875% due April 2033, mandatory tender - October 1, 2021 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 1.875% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 146,000,000 |  |  |  | 146,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 301,000 |  |  |  | 662,000 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes, Pollution Control Revenue Bonds: | 6.25% due January 2038 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 6.25% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 0 |  |  |  | 36,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 0 |  |  |  | 205,000 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes, Pollution Control Revenue Bonds: | 2.125% due June 2040, mandatory tender - June 1, 2022 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 2.125% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 37,000,000 |  |  |  | 37,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 135,000 |  |  |  | 224,000 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes, Pollution Control Revenue Bonds: | 5.20% due June 2040, mandatory tender - June 1, 2020 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 5.20% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 0 |  |  |  | 40,045,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 0 |  |  |  | 17,000 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes, Pollution Control Revenue Bonds: | 5.90% due June 2040 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 5.90% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 0 |  |  |  | 255,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 0 |  |  |  | 1,857,000 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes, Pollution Control Revenue Bonds: | 6.25% due June 2040 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 6.25% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 0 |  |  |  | 11,500,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 0 |  |  |  | 84,000 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes, Pollution Control Revenue Bonds: | 2.45% due September 2042, mandatory tender - June 1, 2022 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 2.45% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 20,000,000 |  |  |  | 20,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 50,000 |  |  |  | 85,000 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes, Pollution Control Revenue Bonds: | 2.40% due June 2043, mandatory tender - June 1, 2020 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 2.40% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 0 |  |  |  | 39,300,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 0 |  |  |  | 50,000 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes, Pollution Control Revenue Bonds: | 5.20% due June 2043, mandatory tender - June 1, 2020 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 5.20% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 0 |  |  |  | 21,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | 0 |  |  |  | 10,000 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes, Pollution Control Revenue Bonds: | Floating rate, weekly-mode |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | 100,345,000 |  |  |  | 0 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 798,000 |  |  |  | 0 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes, Pollution Control Revenue Bonds: | 1.05% due January 2038, mandatory tender - June 1, 2022 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 1.05% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 36,000,000 |  |  |  | 0 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 226,000 |  |  |  | 0 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes, Pollution Control Revenue Bonds: | 1.20% due June 2040, mandatory tender - June 1, 2022 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 1.20% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 11,500,000 |  |  |  | 0 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 72,000 |  |  |  | 0 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes, Pollution Control Revenue Bonds: | 1.10% due June 2040, mandatory tender June 1, 2023 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 1.10% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 130,000,000 |  |  |  | 0 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 892,000 |  |  |  | 0 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes, Pollution Control Revenue Bonds: | 1.15% due June 2040, mandatory tender - June 1, 2024 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 1.15% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 125,000,000 |  |  |  | 0 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 894,000 |  |  |  | 0 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes: | 5.35% due October 2021 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 5.35% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 160,000,000 |  |  |  | 160,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 129,000 |  |  |  | 292,000 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes: | 3.15% due May 2023 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 3.15% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 55,000,000 |  |  |  | 55,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 184,000 |  |  |  | 261,000 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes: | 3.45% due May 2025 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 3.45% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 104,000,000 |  |  |  | 104,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 457,000 |  |  |  | 562,000 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes: | 3.85% due August 2025 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 3.85% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 250,000,000 |  |  |  | 250,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 1,375,000 |  |  |  | 1,675,000 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes: | 3.68% due May 2028 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 3.68% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 88,000,000 |  |  |  | 88,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 457,000 |  |  |  | 518,000 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes: | 3.78% due August 2028 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 3.78% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 15,000,000 |  |  |  | 15,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 80,000 |  |  |  | 91,000 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes: | 3.93% due May 2033 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 3.93% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 38,000,000 |  |  |  | 38,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 221,000 |  |  |  | 238,000 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes: | 4.22% due May 2038 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 4.22% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 45,000,000 |  |  |  | 45,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 275,000 |  |  |  | 291,000 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes: | 4.50% due May 2048 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 4.50% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 20,000,000 |  |  |  | 20,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 128,000 |  |  |  | 133,000 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes: | 4.60% due August 2048 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 4.60% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 85,000,000 |  |  |  | 85,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 550,000 |  |  |  | 570,000 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes: | 3.21% due April 2030 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 3.21% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 150,000,000 |  |  |  | 0 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 1,490,000 |  |  |  | 0 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes: | 3.57% due April 2039 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 3.57% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 50,000,000 |  |  |  | 0 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | 511,000 |  |  |  | 0 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes: | PNM 2019 $250.0 Million Term Loan due July 2020 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Term loans |  |  | 0 |  |  |  | 250,000,000.0 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | 0 |  |  |  | 0 |  |  |
Public Service Company of New Mexico | Senior Unsecured Notes: | PNM 2019 $40.0 Million Term Loan due June 2021 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Term loans |  |  | 40,000,000 |  |  |  | 40,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | 0 |  |  |  | 0 |  |  |
Texas-New Mexico Power Company |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Total |  |  | 843,198,000 |  |  |  | 658,198,000 |  |  |
Principal, less current maturities |  |  | 0 |  |  |  | 0 |  |  |
Long-term debt, excluding current maturities, gross |  |  | 843,198,000 |  |  |  | 658,198,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | (10,475,000) |  |  |  | (12,493,000) |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net, Less current maturities |  |  | 0 |  |  |  | 0 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net, excluding current maturities |  |  | $ (10,475,000) |  |  |  | (12,493,000) |  |  |
Texas-New Mexico Power Company | First Mortgage Bonds: | 6.95% due April 2043 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 6.95% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 93,198,000 |  |  |  | 93,198,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ (15,917,000) |  |  |  | (16,632,000) |  |  |
Texas-New Mexico Power Company | First Mortgage Bonds: | 4.03% due July 2024 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 4.03% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 80,000,000 |  |  |  | 80,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 369,000 |  |  |  | 475,000 |  |  |
Texas-New Mexico Power Company | First Mortgage Bonds: | 3.53% due February 2026 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 3.53% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 60,000,000 |  |  |  | 60,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 420,000 |  |  |  | 502,000 |  |  |
Texas-New Mexico Power Company | First Mortgage Bonds: | 3.22% due August 2027 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 3.22% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 60,000,000 |  |  |  | 60,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 380,000 |  |  |  | 437,000 |  |  |
Texas-New Mexico Power Company | First Mortgage Bonds: | 3.85% due June 2028 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 3.85% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 60,000,000 |  |  |  | 60,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 469,000 |  |  |  | 531,000 |  |  |
Texas-New Mexico Power Company | First Mortgage Bonds: | 3.79% due March 2034 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 3.79% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 75,000,000 |  |  |  | 75,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 497,000 |  |  |  | 535,000 |  |  |
Texas-New Mexico Power Company | First Mortgage Bonds: | 3.92% due March 2039 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 3.92% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 75,000,000 |  |  |  | 75,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 514,000 |  |  |  | 542,000 |  |  |
Texas-New Mexico Power Company | First Mortgage Bonds: | 4.06% due March 2044 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 4.06% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 75,000,000 |  |  |  | 75,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 524,000 |  |  |  | 546,000 |  |  |
Texas-New Mexico Power Company | First Mortgage Bonds: | 3.60% due July 2029 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 3.60% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 80,000,000 |  |  |  | 80,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 511,000 |  |  |  | 571,000 |  |  |
Texas-New Mexico Power Company | First Mortgage Bonds: | 2.73% due April 24, 2030 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 2.73% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 85,000,000 |  |  |  | 0 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 784,000 |  |  |  | 0 |  |  |
Texas-New Mexico Power Company | First Mortgage Bonds: | 3.36% due April 24, 2050 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 3.36% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 25,000,000 |  |  |  | 0 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 243,000 |  |  |  | 0 |  |  |
Texas-New Mexico Power Company | First Mortgage Bonds: | 2.93% due July 15, 2035 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 2.93% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 25,000,000 |  |  |  | 0 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 241,000 |  |  |  | 0 |  |  |
Texas-New Mexico Power Company | First Mortgage Bonds: | 3.36% due July 15, 2050 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 3.36% |  |  |  |  |  |  |
Unsecured long-term debt, noncurrent |  |  | $ 50,000,000 |  |  |  | 0 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | 490,000 |  |  |  | 0 |  |  |
PNMR |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Total |  |  | 745,000,000 |  |  |  | 590,000,000 |  |  |
Principal, less current maturities |  |  | 230,000,000 |  |  |  | 140,000,000 |  |  |
Long-term debt, excluding current maturities, gross |  |  | 515,000,000 |  |  |  | 450,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | 143,000 |  |  |  | 994,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net, Less current maturities |  |  | 52,000 |  |  |  | 0 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net, excluding current maturities |  |  | 91,000 |  |  |  | 994,000 |  |  |
PNMR | PNMR 3.25% 2018 SUNs due March 2021 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Term loans |  |  | $ 300,000,000 |  |  |  | 300,000,000 |  |  |
Stated percentage |  |  | 3.25% |  |  |  |  |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 137,000 |  |  |  | 917,000 |  |  |
PNMR | PNMR Development Term Loan due January 2022 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Term loans |  |  | 65,000,000 |  |  |  | 90,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | 0 |  |  |  | 42,000 |  |  |
PNMR | PNMR 2018 Two-Year Term Loan due December 2020 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Term loans |  |  | 0 |  |  |  | 50,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | 0 |  |  |  | 0 |  |  |
PNMR | PNMR 2019 Term Loan due June 2021 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Term loans |  |  | 150,000,000 |  |  |  | 150,000,000 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | 6,000 |  |  |  | 35,000 |  |  |
PNMR | PNMR 2020 Term Loan due January 2022 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Term loans |  |  | 150,000,000 |  |  |  | 0 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | 0 |  |  |  | 0 |  |  |
PNMR | PNMR 2020 Delayed-Draw Term Loan due January 2022 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Repayments of debt |  | $ 220,000,000.0 |  |  |  |  |  |  |  |
Term loans |  |  | 80,000,000 |  |  |  | 0 |  |  |
Unamortized Discounts, (Premiums), and Issuance Costs, net |  |  | $ 0 |  |  |  | $ 0 |  |  |

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