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Fair Value of Derivative and Other Financial Instruments - Narrative (Details)		4 Months Ended
	Apr. 23, 2024 MW	Sep. 30, 2023 MW	Jun. 30, 2024 USD ($)	Dec. 31, 2023 USD ($)
Debt Securities, Available-for-sale [Line Items]
Obligations to return cash			$ 200,000	$ 200,000
PNM
Debt Securities, Available-for-sale [Line Items]
Amounts recognized for right to reclaim cash			0	0
Cash collateral under margin arrangements			600,000	200,000
PNM \| Recurring
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities			402,386,000
PNM \| Nuclear Decommissioning Trust \| Recurring
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities			370,900,000	361,000,000.0
PNM \| SJGS Decommissioning Trust \| Recurring
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities			9,600,000	12,300,000
PNM \| Mine Reclamation Trust \| Recurring
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities			60,700,000	71,100,000
PNM \| Commodity derivatives \| Designated as Hedging Instrument
Debt Securities, Available-for-sale [Line Items]
Other current assets			846,000	826,000
Current derivative liability			$ 4,558,000	0
PNM \| Portfolio One
Debt Securities, Available-for-sale [Line Items]
Number of megawatts available in purchase power agreement (in megawatts) \| MW	150	85
PNM \| Portfolio Two
Debt Securities, Available-for-sale [Line Items]
Number of megawatts available in purchase power agreement (in megawatts) \| MW	100	50
PNM \| Fuel and purchased power costs \| Commodity derivatives \| Designated as Hedging Instrument
Debt Securities, Available-for-sale [Line Items]
Other current assets				800,000
Current derivative liability				$ 0