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Fair Value of Derivative and Other Financial Instruments - Narrative (Details) | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2021 USD ($) | Dec. 31, 2021 USD ($) MWh MW power_purchase_agreement | Dec. 31, 2020 USD ($) MWh | Dec. 31, 2019 USD ($) | Jan. 01, 2018 MW
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Contract in a net liability position |  | $ 0 | $ 0 |  |
Available for sale securities realized impairment losses |  | $ 700,000 | (3,200,000) | $ 3,000,000 |
Minimum |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Investment allocation targets distribution period |  | 10 years |  |  |
Maximum |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Investment allocation targets distribution period |  | 15 years |  |  |
Equity Securities | Pension Plan |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Investment allocation targets |  | 35.00% |  |  |
Alternative Investments | Pension Plan |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Investment allocation targets |  | 15.00% |  |  |
Fixed income | Pension Plan |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Investment allocation targets |  | 50.00% |  |  |
PNM |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Number of purchase power agreements | power_purchase_agreement |  | 3 |  |  |
Expected exposure to market risk (in megawatts) | MW |  | 65 |  |  | 65
Power to be sold to third party (in megawatts) | MW |  | 36 |  |  | 36
Amounts recognized for the legal right to reclaim cash collateral |  | $ 0 | 0 |  |
Amounts posted as cash collateral under margin arrangements |  | 500,000 |  |  |
Obligations to return cash collateral |  | $ 900,000 | $ 900,000 |  |
PNM | Natural Gas Cost | Unusual Weather |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Cost of energy and production costs | $ 20,000,000 |  |  |  |
PNM | Electricity, Purchased | Unusual Weather |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Cost of energy and production costs | $ 8,000,000 |  |  |  |
PNM | Commodity Contract | Fair Value Hedging |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Power-related contracts (MWh) | MWh |  | 122,400 | 0 |  |
PNM | Commodity Contract | Designated as hedging instrument |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Derivative asset, fair value, gross liability |  | $ 500,000 | $ 1,600,000 |  |
Derivative asset, fair value, gross asset |  | 500,000 | 1,600,000 |  |
Other current assets |  | 684,000 | 1,096,000 |  |
Current derivative liability |  | 2,275,000 | 1,096,000 |  |
PNM | Commodity Contract | Designated as hedging instrument | Cost of Sales |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Gain (loss) on derivative |  | 100,000 | 100,000 |  |
PNM | Fuel and purchased power costs | Commodity Contract | Designated as hedging instrument |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Other current assets |  | 200,000 | 0 |  |
Current derivative liability |  | $ 1,800,000 | 0 |  |
PNM | Portfolio One |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Number of megawatts available in purchase power agreement (in megawatts) | MW |  | 85 |  |  |
PNM | Portfolio Three |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Number of megawatts available in purchase power agreement (in megawatts) | MW |  | 40 |  |  |
PNM | Portfolio Two |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Number of megawatts available in purchase power agreement (in megawatts) | MW |  | 150 |  |  |
PNM | Tri-State |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Power to be sold to third party (in megawatts) | MW |  | 100 |  |  |
Texas-New Mexico Power Company |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Cost of energy and production costs |  | $ 113,067,000 | 102,074,000 | $ 95,087,000 |
Texas-New Mexico Power Company | Equity Securities | Pension Plan |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Investment allocation targets |  | 16.00% |  |  |
Texas-New Mexico Power Company | Alternative Investments | Pension Plan |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Investment allocation targets |  | 14.00% |  |  |
Texas-New Mexico Power Company | Fixed income | Pension Plan |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Investment allocation targets |  | 70.00% |  |  |
Measured on a recurring basis | PNM |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Debt securities, available-for-sale |  | $ 463,126,000 | 440,115,000 |  |
Nuclear Decommissioning Trust | Measured on a recurring basis | PNM |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Debt securities, available-for-sale |  | 394,500,000 | 379,200,000 |  |
Mine Reclamation Trust | Measured on a recurring basis | PNM |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Debt securities, available-for-sale |  | $ 68,600,000 | $ 60,900,000 |  |

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