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Regulatory and Rate Matters - SJGS, Fours Corners and PVNGS Leased Interest Abandonment Applications (Details) $ in Thousands |  |  |  |  |  | 1 Months Ended |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
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Apr. 02, 2021 lease MW | Feb. 03, 2021 | Jan. 08, 2021 USD ($) | Nov. 01, 2020 USD ($) | Jul. 01, 2019 USD ($) | Nov. 30, 2020 USD ($) | Jul. 28, 2021 MW | Jul. 22, 2021 resource_project MW | Jun. 30, 2021 USD ($) MW | Jun. 23, 2021 MW | May 27, 2021 MW | Apr. 14, 2021 MW | Mar. 12, 2021 MW | Feb. 08, 2021 MW | Jan. 28, 2021 MW | Dec. 31, 2020 USD ($) | Dec. 18, 2020 USD ($) | Nov. 13, 2020 MW | Sep. 28, 2020 USD ($) | Jul. 29, 2020 MW | Mar. 31, 2020 USD ($) | Feb. 21, 2020 USD ($)
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory time frame for proposed PPAs and battery storage agreements | 6 months |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage |  |  |  |  |  |  |  |  | 50.00% |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets | $ |  |  |  |  |  |  |  |  | $ 549,286 |  |  |  |  |  |  | $ 557,790 |  |  |  |  |  |
Regulatory liabilities | $ |  |  |  |  |  |  |  |  | 852,655 |  |  |  |  |  |  | 850,228 |  |  |  |  |  |
COVID-19 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Temporary mandatory moratorium on disconnection period |  | 100 days |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disconnection transition period |  | 90 days |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Facebook Data Center |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Solar generation capacity (in megawatts) |  |  |  |  |  |  |  |  |  |  |  |  |  | 190 |  |  |  |  |  |  |  |
Number of megawatts in battery storage facilities (in megawatts) |  |  |  |  |  |  |  |  |  | 100 |  | 100 |  | 100 |  |  |  |  |  |  |  |
Solar generation capacity expected to be operational (in megawatts) |  |  |  |  |  |  |  |  |  |  |  |  |  | 50 |  |  |  |  |  |  |  |
Facebook Data Center | Subsequent event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Solar generation capacity (in megawatts) |  |  |  |  |  |  | 190 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatts in battery storage facilities (in megawatts) |  |  |  |  |  |  | 100 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Solar generation capacity expected to be operational (in megawatts) |  |  |  |  |  |  | 50 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatts in battery storage facilities approved (in megawatts) |  |  |  |  |  |  | 50 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatts in battery storage facilities disapproved (in megawatts) |  |  |  |  |  |  | 50 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Solar generation capacity (in megawatts) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 650 |  |
Number of megawatts in battery storage facilities (in megawatts) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 300 |  |
Number of leases under which lease term was extended | lease | 5 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets | $ |  |  |  |  |  |  |  |  | 454,151 |  |  |  |  |  |  | 457,953 |  |  |  |  |  |
Regulatory liabilities | $ |  |  |  |  |  |  |  |  | 663,245 |  |  |  |  |  |  | 664,873 |  |  |  |  |  |
Solar generation capacity related to unexecuted transmission service agreement (in megawatts) |  |  |  |  |  |  |  |  |  |  |  |  | 145 |  |  |  |  |  |  |  |  |
PNM | Subsequent event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of additional approved replacement resource projects | resource_project |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNM | Four Corners |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Request issuance of energy transition bonds | $ |  |  | $ 300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forecasted undepreciated investment | $ |  |  | 272,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Plant decommissioning and coal mine reclamation costs | $ |  |  | 4,600 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Upfront financing costs | $ |  |  | 7,300 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from securitization bonds | $ |  |  | $ 16,500 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Solar generation capacity (in megawatts) |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 200 |  |  |  |  |  |  |
Payments for relief from obligations | $ |  |  |  | $ 75,000 |  | $ 15,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Final payment for relief from obligations | $ |  |  |  |  |  | 60,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Initial payment for relief from obligations | $ |  |  |  |  |  | $ 15,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNM | Four Corners | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Noncontrolling interest, ownership percentage by noncontrolling owners |  |  |  | 13.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNM | COVID-19 | COVID-19 Costs Savings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 900 |  |  |  |  |  |
PNM | Deferred COVID-19 Costs | COVID-19 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets | $ |  |  |  |  |  |  |  |  | $ 12,200 |  |  |  |  |  |  | 8,800 |  |  |  |  |  |
PNM | NMPRC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Solar generation capacity, amount requested for approval to abandon (in megawatts) | 114 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNM | Leased Interest Termination on January 15, 2023 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of leases under which lease term was extended | lease | 4 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNM | Leased Interest Termination on January 15, 2023 | NMPRC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Solar generation capacity (in megawatts) | 104 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNM | Leased Interest Termination on January 15, 2024 | NMPRC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Solar generation capacity (in megawatts) | 10 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNM | Replacement Resource Portfolio One |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Solar generation capacity (in megawatts) | 150 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 200 |  |  |  |
Number of megawatts in battery storage facilities (in megawatts) | 40 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100 |  |  |  |
PNM | Replacement Resource Portfolio One | Subsequent event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Solar generation capacity (in megawatts) |  |  |  |  |  |  |  | 200 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatts in battery storage facilities (in megawatts) |  |  |  |  |  |  |  | 100 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatts available in battery storage facilities (in megawatts) |  |  |  |  |  |  |  | 50 |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNM | Replacement Resource Portfolio Two |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Solar generation capacity (in megawatts) |  |  |  |  |  |  |  |  |  |  | 100 |  |  |  |  |  |  | 100 |  |  |  |
Number of megawatts in battery storage facilities (in megawatts) | 100 |  |  |  |  |  |  |  |  |  | 30 |  |  |  |  |  |  | 30 |  |  |  |
PNM | Replacement Resource Portfolio Two | Subsequent event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Solar generation capacity (in megawatts) |  |  |  |  |  |  |  | 300 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatts in battery storage facilities (in megawatts) |  |  |  |  |  |  |  | 150 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatts available in battery storage facilities (in megawatts) |  |  |  |  |  |  |  | 150 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatts available in solar facilities (in megawatts) |  |  |  |  |  |  |  | 150 |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNM | Replacement Resource Portfolio Three |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Solar generation capacity (in megawatts) | 300 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatts in battery storage facilities (in megawatts) | 150 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNM | Transportation Electrification Program |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Expected budgeted expenditures | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 8,400 |  |  |  |  |
Budget flexibility (percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 25.00% |  |  |  |  |
Budget portion dedicated to low and moderate income customers (percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 25.00% |  |  |  |  |
PNMR Development |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Solar generation capacity (in megawatts) |  |  |  |  |  |  |  |  | 130 |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage |  |  |  |  |  |  |  |  | 50.00% |  |  |  |  |  |  |  |  |  |  |  |  |
San Juan Generating Station |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated costs of replacement resources | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 8,100 |  |  |
San Juan Generating Station | Other deferred credits |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Restructuring reserve | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 38,100 |  |  |  |  |  |
San Juan Generating Station | Employee Severance |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Restructuring reserve | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 9,400 |
San Juan Generating Station | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Request issuance of energy transition bonds | $ |  |  |  |  | $ 361,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forecasted undepreciated investment | $ |  |  |  |  | 283,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 361,000
Plant decommissioning and coal mine reclamation costs | $ |  |  |  |  | 28,600 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Upfront financing costs | $ |  |  |  |  | 9,600 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Severance costs | $ |  |  |  |  | 20,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from securitization bonds | $ |  |  |  |  | $ 19,800 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
San Juan Generating Station | PNM | Other deferred credits |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Restructuring reserve | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 36,800 |  |  |  |  |  |
San Juan Generating Station | PNM | Employee Severance |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Restructuring reserve | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8,100 |
San Juan Generating Station | PNM | Other Restructuring |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Restructuring reserve | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8,900 |
San Juan Generating Station | PNM | Economic Development and Workforce Training Costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Restructuring reserve | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 19,800 |

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