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Regulatory and Rate Matters - PNM (Details) |  |  |  |  |  |  |  |  |  | 1 Months Ended | 3 Months Ended | 6 Months Ended | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jun. 01, 2020 USD ($) | May 28, 2020 USD ($) | Apr. 15, 2020 USD ($) MMBTU meter | Feb. 01, 2018 | Jan. 10, 2018 USD ($) | Jul. 03, 2017 | Dec. 07, 2016 USD ($) | Sep. 28, 2016 USD ($) lease MW | Aug. 27, 2015 USD ($) | Aug. 31, 2016 USD ($) lease MW | Jun. 30, 2020 USD ($) MW | Sep. 30, 2019 | Jun. 30, 2019 USD ($) | Mar. 31, 2019 USD ($) | Jun. 30, 2020 USD ($) MW | Jun. 30, 2019 USD ($) | Dec. 31, 2019 USD ($) GWh | Dec. 31, 2017 | Mar. 27, 2020 MW | May 16, 2019 MW | Sep. 30, 2016 MW | Jan. 31, 2016 MW
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income taxes (benefit) |  |  |  |  |  |  |  |  |  |  | $ (4,275,000) |  | $ 42,831,000 |  | $ (2,395,000) | $ 41,608,000 |  |  |  |  |  |
Regulatory disallowances and restructuring costs |  |  |  |  |  |  |  |  |  |  | $ 0 |  | 149,254,000 |  | $ 0 | 150,599,000 |  |  |  |  |  |
Percent of non-fuel revenue requirement change implemented |  |  |  | 50.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Excess return on jurisdictional equity that would require refund |  |  |  |  |  |  |  |  |  |  | 0.50% |  |  |  | 0.50% |  |  |  |  |  |  |
PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income taxes (benefit) |  |  |  |  |  |  |  |  |  |  | $ (4,895,000) |  | 43,481,000 |  | $ (2,536,000) | 41,508,000 |  |  |  |  |  |
Regulatory disallowances and restructuring costs |  |  |  |  |  |  |  |  |  |  | $ 0 |  | 149,254,000 |  | $ 0 | 150,599,000 |  |  |  |  |  |
Solar generation capacity (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 300 |  |  |
Action plan, covered period |  |  |  |  |  | 4 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2015 Electric Rate Case | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested rate increase (decrease) |  |  |  |  |  |  |  |  | $ 123,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Requested rate increase (decrease) of non-fuel revenue |  |  |  |  |  |  |  |  | $ 121,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Approved rate increase (decrease) |  |  |  |  |  |  |  | $ 61,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Renewable Portfolio Standard | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatts of Solar PV facilities | MW |  |  |  |  |  |  |  |  |  |  | 157 |  |  |  | 157 |  |  |  |  |  |  |
Current output in the geothermal facility (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  | 15 |  |  |  | 15 |  |  |  |  |  |  |
Solar generation capacity (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  | 138.6 |  |  |  | 138.6 |  |  |  |  |  |  |
Energy Efficiency and Load Management Program | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Energy efficiency and load management programs targeted energy savings (in Gigawatts) | MMBTU |  |  | 80 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Program costs related to energy efficiency, in year two |  |  | $ 31,400,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Program costs related to energy efficiency, in year three |  |  | 31,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Program costs related to energy efficiency, in year four |  |  | $ 29,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of AMI meters to be installed | meter |  |  | 5,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Program costs related to meter installation |  |  | $ 2,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Integrated Resource Plan, 2011 | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Frequency of IRP filings |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3 years |  |  |  |  |  |  |
Planning period covered of IRP |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20 years |  |  |  |  |  |  |
Integrated Resource Plan, 2017 | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Planning period covered of IRP |  |  |  |  |  | 20 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Integrated Resource Plan, 2020 | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Planning period covered of IRP |  |  |  |  |  |  |  |  |  |  |  | 20 years |  |  |  |  |  |  |  |  |  |
NMPRC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested rate increase (decrease) |  |  |  |  |  |  | $ 99,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested return on equity |  |  |  |  |  |  | 10.125% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period of time for proposed return to customers the benefit of the reduction in New Mexico's corporate income tax rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3 years |  |  |  |
Action plan, covered period |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4 years |  |  |  |  |  |  |
NMPRC | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested rate increase (decrease) |  |  |  |  | $ 10,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested return on equity |  |  |  |  | 9.575% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period of time for proposed return to customers the benefit of the reduction in New Mexico's corporate income tax rate |  |  |  |  | 3 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proposed revision to rider that will allow for recovery |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 49,600,000 |  |  |  |  |
NMPRC | Renewable Energy Rider | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proposed revision to rider that will allow for recovery | $ 67,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue from renewable energy rider, year two |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 58,900,000 |  |  |  |  |  |  |
Recorded revenues from renewable rider |  |  |  |  |  |  |  |  |  |  | $ 15,200,000 |  | $ 12,800,000 |  | $ 30,300,000 | 25,500,000 |  |  |  |  |  |
NMPRC | Renewable Energy Rider, Sky Blue Energy Program | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proposed revision to rider that will allow for recovery | $ 2,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Required Percentage by 2011 | Renewable Portfolio Standard | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Required percentage of renewable energy in portfolio to electric sales |  |  |  |  |  |  |  |  |  |  | 10.00% |  |  |  | 10.00% |  |  |  |  |  |  |
Required Percentage by 2015 | Renewable Portfolio Standard | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Required percentage of renewable energy in portfolio to electric sales |  |  |  |  |  |  |  |  |  |  | 15.00% |  |  |  | 15.00% |  |  |  |  |  |  |
Required Percentage by 2020 | Renewable Portfolio Standard | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Required percentage of renewable energy in portfolio to electric sales |  |  |  |  |  |  |  |  |  |  | 20.00% |  |  |  | 20.00% |  |  |  |  |  |  |
Minimum | Renewable Portfolio Standard | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Profit incentive sliding scale multiplier |  |  | 0.071 |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.071 |  |  |  |  |
Energy efficiency and load management programs targeted energy savings (in Gigawatts) | MMBTU |  |  | 80 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum | Renewable Portfolio Standard | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reasonable cost threshold in megawatts per hour |  |  |  |  |  |  |  |  |  |  | $ 60 |  |  |  | $ 60 |  |  |  |  |  |  |
Palo Verde Nuclear Generating Station, Unit 2 Leases | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatts purchased (in megawatts) | MW |  |  |  |  |  |  |  | 64.1 |  | 64.1 |  |  |  |  |  |  |  |  |  |  | 64.1 | 64.1
Number of megawatts nuclear generation (in megawatts) | MW |  |  |  |  |  |  |  | 114.6 |  | 114.6 |  |  |  |  |  |  |  |  |  | 114.6 | 114.6 |
Number of leases under which assets were purchased | lease |  |  |  |  |  |  |  | 3 |  | 3 |  |  |  |  |  |  |  |  |  |  |  |
Public utilities, aggregate annual rent expense |  |  |  |  |  |  |  |  |  | $ 18,100,000 |  |  |  |  |  |  |  |  |  |  |  |
Palo Verde Nuclear Generating Station, Unit 2 Leases | 2015 Electric Rate Case | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Hearing examiner's proposed disallowance of recovery |  |  |  |  |  |  |  |  |  | $ 163,300,000 |  |  |  |  |  |  |  |  |  |  |  |
Initial rate base value |  |  |  |  |  |  |  | $ 83,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disallowance of the recovery undepreciated costs of capitalized leasehold improvements |  |  |  |  |  |  |  | $ 43,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax regulatory disallowance |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 19,700,000 |  |  |  |  |  |  |  |
New Mexico Wind | Renewable Portfolio Standard 2014 | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatts for wind energy | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 204 |  |  |  |  |  |  |
Red Mesa Wind | Renewable Portfolio Standard 2014 | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatts for wind energy | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 102 |  |  |  |  |  |  |
La Joya Wind | Renewable Portfolio Standard | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatts for wind energy | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 140 |  |  |  |  |  |  |
Four Corners |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory disallowances and restructuring costs |  |  |  |  | $ 47,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory disallowance |  |  |  |  | $ 148,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
New Mexico 2015 Rate Case | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax impairment of investments |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,300,000 |  | $ 150,600,000 |  |  |  |  |  |
Undepreciated capitalized improvements |  |  |  |  |  |  |  |  |  |  | $ 39,700,000 |  |  |  | $ 39,700,000 |  |  |  |  |  |  |
New Mexico 2015 Rate Case | Palo Verde Nuclear Generating Station, Unit 2 Leases | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatts purchased (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  | 64.1 |  |  |  | 64.1 |  |  |  |  | 64.1 |  |
Portion of purchase price |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 73,200,000 |  |  |  |  |  |  |
Income taxes (benefit) |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 45,700,000 |  |  |  |  |  |  |
Leaseholds and Leasehold Improvements | New Mexico 2015 Rate Case | Palo Verde Nuclear Generating Station, Unit 1 and 4 Leases | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Undepreciated capitalized improvements |  |  |  |  |  |  |  |  |  |  | $ 37,700,000 |  |  |  | $ 37,700,000 |  |  |  |  |  |  |
Disincentives and Incentives Added | 2017 Energy Efficiency and Load Management Program | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Energy efficiency and load management programs profit incentive, minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,800,000 |  |  |  |  |
Energy efficiency and load management programs targeted energy savings (in Gigawatts) | GWh |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 59 |  |  |  |  |
Energy efficiency and load management programs additional incentive targeted energy savings (in Gigawatts) | GWh |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 68 |  |  |  |  |
Disincentives and Incentives Added | 2019 Energy Efficiency and Load Management Program | PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Energy efficiency and load management programs profit incentive, minimum |  | $ 500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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