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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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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]
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