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Fair Value of Derivative and Other Financial Instruments - Narrative (Details) |  |  | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | ---
Mar. 18, 2022 MW | Feb. 17, 2022 MW | Mar. 31, 2022 USD ($) MW gal | Mar. 31, 2021 USD ($) | Dec. 31, 2021 USD ($) MW power_purchase_agreement | Dec. 31, 2021 USD ($) MWh MW power_purchase_agreement gal
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Number of purchase power agreements | power_purchase_agreement |  |  |  |  | 3 |
Number of purchase power agreements, non derivatives | power_purchase_agreement |  |  |  |  |  | 2
Obligations to return cash |  |  | $ 900,000 |  | $ 900,000 | $ 900,000
Contract in a liability position |  |  | 0 |  | 0 | 0
Debt securities, available-for-sale, unrealized loss position |  |  | 0 |  | 0 | 0
Other than temporary impairments |  |  | $ 0 |  |  | $ 0
PNM |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Number of purchase power agreements | power_purchase_agreement |  |  |  |  |  | 3
Number of megawatts available in purchase power agreement (in megawatts) | MW | 65 | 327 |  |  |  |
Expected exposure to market risk (in megawatts) | MW |  |  | 65 |  |  |
Power to be sold to third party (in megawatts) | MW |  |  | 36 |  |  |
Amounts recognized for right to reclaim cash |  |  | $ 0 |  | 0 | $ 0
Cash collateral under margin arrangements |  |  | 500,000 |  | 500,000 | $ 500,000
(Increase)/decrease in other than temporary losses of available-for-sale securities, net portion recognized in earnings |  |  | $ (8,900,000) | $ 1,100,000 |  |
PNM | Natural Gas Cost | Unusual Weather |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Cost of energy |  |  |  | 20,000,000 |  |
PNM | Electricity, Purchased | Unusual Weather |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Cost of energy |  |  |  | 8,000,000 |  |
PNM | Commodity derivatives | Fair value hedging |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Economic Hedges (in mmbtu and mwh) | MWh |  |  |  |  |  | 122,400
Open gas commodity volume positions | gal |  |  | 0 |  |  | 0
PNM | Commodity derivatives | Designated as Hedging Instrument |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Derivative asset, gross liability |  |  | $ 200,000 |  |  |
Derivative asset, gross asset |  |  |  |  | 500,000 | $ 500,000
Other current assets |  |  | 183,000 |  | 684,000 | 684,000
Current derivative liability |  |  | 3,852,000 |  | $ 2,275,000 | $ 2,275,000
PNM | Commodity derivatives | Designated as Hedging Instrument | Cost of energy |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Total gain |  |  | 100,000 | $ 100,000 |  |
PNM | Portfolio One |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Number of megawatts available in purchase power agreement (in megawatts) | MW |  |  |  |  | 85 | 85
PNM | Portfolio Three |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Number of megawatts available in purchase power agreement (in megawatts) | MW |  |  |  |  | 40 | 40
PNM | Portfolio Two |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Number of megawatts available in purchase power agreement (in megawatts) | MW |  |  |  |  | 150 | 150
PNM | Fuel and purchased power costs | Commodity derivatives | Designated as Hedging Instrument |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Other current assets |  |  | 0 |  | $ 200,000 | $ 200,000
Current derivative liability |  |  | $ 3,700,000 |  | 1,800,000 | 1,800,000
PNM | Tri-State |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Power to be sold to third party (in megawatts) | MW |  |  | 100 |  |  |
PNM | Recurring |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Available-for-sale debt securities |  |  | $ 431,097,000 |  | 463,126,000 | 463,126,000
Nuclear Decommissioning Trust | PNM | Recurring |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Available-for-sale debt securities |  |  | 364,100,000 |  | 394,500,000 | 394,500,000
Mine Reclamation Trust | PNM | Recurring |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Available-for-sale debt securities |  |  | $ 67,000,000 |  | $ 68,600,000 | $ 68,600,000

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