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- Definition

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

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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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Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

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No definition available.

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Amount of realized gain on 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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Amount of realized loss on 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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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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- 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

Amount of transfer of financial instrument classified as an asset into (out of) level 3 of the fair value hierarchy.

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- Definition

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

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Amount of cash inflow from sale 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

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 - Non-Derivative Financial Instruments (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018	Jan. 01, 2017
Debt Securities, Available-for-sale [Line Items]
Cumulative effect adjustment				$ 0	$ 10,382,000
Available for sale securities realized impairment losses	$ 3,000,000.0	$ 9,400,000	$ 3,300,000
Debt securities, unrealized loss position	0
Transfer to fair value hierarchy Level 2		0
PNMR and PNM
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale	249,818,000
Proceeds from sales	494,528,000	984,533,000	637,492,000
Gross realized gains	25,760,000	19,358,000	36,896,000
Gross realized (losses)	(17,453,000)	(16,624,000)	$ (12,993,000)
Impairment losses other than temporary included in AOCI	0
Nuclear Decommissioning Trust \| Measured on a recurring basis \| PNMR and PNM
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale	336,000,000.0	287,100,000
Mine Reclamation Trust \| Measured on a recurring basis \| PNMR and PNM
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale	$ 52,800,000	$ 41,100,000
Retained Earnings
Debt Securities, Available-for-sale [Line Items]
Cumulative effect adjustment				11,208,000	$ 10,382,000
Accounting Standards Update 2016-01 \| Retained Earnings
Debt Securities, Available-for-sale [Line Items]
Cumulative effect adjustment				$ 11,200,000
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
Pension Plan \| Equity Securities
Debt Securities, Available-for-sale [Line Items]
Investment allocation targets	30.00%
Pension Plan \| Alternative Investments
Debt Securities, Available-for-sale [Line Items]
Investment allocation targets	20.00%
Pension Plan \| Fixed income
Debt Securities, Available-for-sale [Line Items]
Investment allocation targets	50.00%