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Commitments and Contingencies - Coal Supply (Details) - USD ($) | 9 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Sep. 30, 2023 | Dec. 31, 2022 | Jan. 31, 2016
PNM | Loss on long-term purchase commitment | Surface |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |
Loss contingency accrual | $ 52,900,000 | $ 62,600,000 |
PNM | Loss on long-term purchase commitment | Underground |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |
Loss contingency accrual | 28,900,000 | 28,200,000 |
PNM | Loss on long-term purchase commitment | San Juan Generating Station | Surface |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |
Estimate of possible loss | 56,800,000 |  |
PNM | Loss on long-term purchase commitment | San Juan Generating Station | Underground |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |
Estimate of possible loss | 33,300,000 |  |
Coal supply | San Juan Generating Station |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |
Cash used to support bank letter or credit arrangement |  |  | $ 30,300,000
Coal supply | NM Capital | San Juan Generating Station |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |
Requirement to post reclamation bonds | 118,700,000 |  |
Cash used to support bank letter or credit arrangement | 30,300,000 |  |
Four Corners CSA | PNM |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |
Funds contributed, mine reclamation trust |  | 2,400,000 |
Reclamation trust funding, remainder of year | 200,000 |  |
San Juan Generating Station | Loss on long-term purchase commitment | PNM |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |
Annual funding post-term reclamation trust |  | $ 10,000,000 |
Annual funding post-term reclamation trust, remainder of year | 0 |  |
Annual funding post-term reclamation trust, year one | 0 |  |
Annual funding post-term reclamation trust, year two | 0 |  |
San Juan Generating Station and Four Corners | Mine Reclamation Trust | PNM |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |
Customer reclamation funding cost | $ 100,000,000 |  |

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