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- Definition

Defined Benefit Plan, Periodic Distribution Period

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No definition available.

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- Definition

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

+ References

No definition available.

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- Definition

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

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No definition available.

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- Definition

Public Utilities, Concentration Risk, Potential Market Risk

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No definition available.

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- Definition

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

Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

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- Definition

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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- Definition

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

+ References

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- Definition

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

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- Definition

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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- Definition

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.

+ References

No definition available.

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Fair Value of Derivative and Other Financial Instruments - Narrative (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) MW	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 MW
Debt Securities, Available-for-sale [Line Items]
Contract in a net liability position	$ 0	$ 0
Available for sale securities realized impairment losses	$ (3,200,000)	3,000,000.0	$ (9,400,000)
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]
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	500,000
Obligations to return cash collateral	900,000	900,000
PNM \| Commodity Contract \| Designated as hedging instrument
Debt Securities, Available-for-sale [Line Items]
Other current assets	1,096,000	1,089,000
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	$ 0	0
PNM \| Tri-State
Debt Securities, Available-for-sale [Line Items]
Power to be sold to third party (in megawatts) \| MW	100
Measured on a recurring basis \| PNM
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale	$ 440,115,000	388,832,000
Nuclear Decommissioning Trust \| Measured on a recurring basis \| PNM
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale	379,200,000	336,000,000.0
Mine Reclamation Trust \| Measured on a recurring basis \| PNM
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale	$ 60,900,000	$ 52,800,000