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(Increase)/Decrease In Other Than Temporary Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities

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Public Utilities, Concentration Risk, Amount To Sell Due To Agreement

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Public Utilities, Concentration Risk, Potential Market Risk

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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- Definition

The aggregate costs related to goods produced and sold and services rendered by an entity during the reporting period. This excludes costs incurred during the reporting period related to financial services rendered and other revenue generating activities.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss.

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Fair value, after the effects of master netting arrangements, of a financial asset or other 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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- Definition

Amount of obligation to return cash collateral under master netting arrangements that have not been offset against derivative assets.

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Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities.

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

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Nominal energy measure used to calculate payments on a derivative instrument.

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The amount of cash or securities placed with a broker or counterparty as security for a trading or derivatives securities position which was partially obtained with funds provided by the broker dealer.

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Amount before tax of other than temporary impairment (OTTI) loss on investments in available-for-sale and held-to-maturity debt securities, recognized in other comprehensive loss.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Fair Value of Derivative and Other Financial Instruments - Narrative (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2021 USD ($) MMBTU MW	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($) MMBTU
Debt Securities, Available-for-sale [Line Items]
Obligations to return cash	$ 900,000		$ 900,000
Contract in a liability position	0		0
Debt securities, available-for-sale, unrealized loss position	0		0
Other than temporary impairments	$ 0		0
PNM
Debt Securities, Available-for-sale [Line Items]
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
Cash collateral under margin arrangements	500,000		$ 500,000
(Increase)/decrease in other than temporary losses of available-for-sale securities, net portion recognized in earnings	1,100,000	$ (12,700,000)
PNM \| Electricity, Purchased \| Unusual Weather
Debt Securities, Available-for-sale [Line Items]
Cost of energy	20,000,000
PNM \| Natural Gas Cost \| 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) \| MMBTU	0		0
PNM \| Commodity derivatives \| Designated as Hedging Instrument
Debt Securities, Available-for-sale [Line Items]
Other current assets	$ 1,097,000		$ 1,096,000
PNM \| Commodity derivatives \| Designated as Hedging Instrument \| Cost of energy
Debt Securities, Available-for-sale [Line Items]
Total gain	100,000	$ 100,000
PNM \| Fuel and purchased power costs \| Commodity derivatives \| Designated as Hedging Instrument
Debt Securities, Available-for-sale [Line Items]
Other current assets	$ 0		0
PNM \| Tri-State
Debt Securities, Available-for-sale [Line Items]
Power to be sold to third party (in megawatts) \| MW	100
Recurring \| PNM
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities	$ 437,028,000		440,115,000
Nuclear Decommissioning Trust \| Recurring \| PNM
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities	376,800,000		379,200,000
Mine Reclamation Trust \| Recurring \| PNM
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities	$ 60,200,000		$ 60,900,000