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Summary of the Business and Significant Accounting Policies - Narrative (Details) | 12 Months Ended
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Dec. 31, 2021 USD ($) utility | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($)
Accounting Policies Disclosures [Line Items] |  |  |
Payment defaults | $ 0 |  |
Allowance for equity funds used during construction | $ 13,217,000 | $ 11,254,000 | $ 9,478,000
PNMR |  |  |
Accounting Policies Disclosures [Line Items] |  |  |
Number of regulated utilities | utility | 2 |  |
Restricted cash | $ 0 | 0 |
Public Service Company of New Mexico |  |  |
Accounting Policies Disclosures [Line Items] |  |  |
Restricted cash | 0 | 0 |
Allowance for funds used during construction, capitalized interest | $ 3,400,000 | $ 3,000,000 | $ 5,000,000
Allowance for funds used during construction, capitalized interest rate | 1.70% | 2.40% | 2.99%
Allowance for equity funds used during construction | $ 9,905,000 | $ 6,958,000 | $ 6,656,000
Allowance for funds used during construction, capitalized cost of equity rate | 4.94% | 3.42% | 3.95%
Impairment losses on securities held in the NDT | $ (700,000) | $ 3,200,000 | $ 5,700,000
Texas-New Mexico Power Company |  |  |
Accounting Policies Disclosures [Line Items] |  |  |
Restricted cash | 0 | 0 |
Allowance for funds used during construction, capitalized interest | $ 1,600,000 | $ 2,100,000 | $ 2,400,000
Allowance for funds used during construction, capitalized interest rate | 1.80% | 2.20% | 3.23%
Allowance for equity funds used during construction | $ 3,300,000 | $ 4,300,000 | $ 2,800,000
Allowance for funds used during construction, capitalized cost of equity rate | 3.67% | 4.42% | 3.78%

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- Definition Amount of other-than-temporary impairment (OTTI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), recognized in earnings and other comprehensive loss (OCI). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 8A -URI http://asc.fasb.org/extlink&oid=124260329&loc=SL6284422-111562 + Details
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