Fair Value of Derivative and Other Financial Instruments - Narrative (Details)				1 Months Ended	3 Months Ended		6 Months Ended	9 Months Ended		12 Months Ended
	Mar. 18, 2022 MW	Feb. 17, 2022 MW	Nov. 15, 2015 power_purchase_agreement	Jun. 30, 2022 MW	Sep. 30, 2022 USD ($) MW	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($) power_purchase_agreement MW	Sep. 30, 2022 USD ($) MW	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($) MW power_purchase_agreement	May 31, 2022 MW	Jan. 01, 2018 MW
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					$ 200,000		$ 900,000	$ 200,000		$ 900,000
Contractual liability					20,100,000		0	20,100,000		$ 0
Cash collateral					0			0
Net exposure					$ 14,900,000			$ 14,900,000
PNM
Debt Securities, Available-for-sale [Line Items]
Expected exposure to market risk (in megawatts) | MW					36			36			50	65
Number of purchase power agreements | power_purchase_agreement			2							3
Number of megawatts available in purchase power agreement (in megawatts) | MW	65	327		35
Amounts recognized for right to reclaim cash					$ 0		0	$ 0		$ 0
Cash collateral under margin arrangements					500,000		500,000	500,000		500,000
(Increase)/decrease in other than temporary losses of available-for-sale securities, net portion recognized in earnings					(7,100,000)	$ 600,000		(28,700,000)	$ 1,200,000
PNM | Commodity derivatives | Designated as Hedging Instrument
Debt Securities, Available-for-sale [Line Items]
Derivative asset, gross asset							500,000			500,000
Other current assets					5,466,000		684,000	5,466,000		684,000
Other deferred charges					170,000		0	170,000		0
Other deferred credits					2,723,000		0	2,723,000		0
Current derivative liability					17,346,000		$ 2,275,000	17,346,000		$ 2,275,000
Total gain					$ 100,000	$ 100,000		$ 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					125		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			40
PNM | Portfolio Two
Debt Securities, Available-for-sale [Line Items]
Number of megawatts available in purchase power agreement (in megawatts) | MW					35		150			150
PNM | Fuel and purchased power costs | Commodity derivatives | Designated as Hedging Instrument
Debt Securities, Available-for-sale [Line Items]
Other current assets							$ 200,000			$ 200,000
Current derivative liability							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			100
PNM | Recurring
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities					$ 376,662,000		463,126,000	$ 376,662,000		463,126,000
Nuclear Decommissioning Trust | PNM | Recurring
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities					310,200,000		394,500,000	310,200,000		394,500,000
Mine Reclamation Trust | PNM | Recurring
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities					$ 66,500,000		$ 68,600,000	$ 66,500,000		$ 68,600,000