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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