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Commitments and Contingencies - Coal Supply (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Jan. 31, 2016
Other Commitments [Line Items] |  |  |  |
Coal requirement, minimum required payment, year one | $ 39.9 |  |  |
Coal requirement, minimum required payment, year two | 81.8 |  |  |
Public Utilities, Coal Requirement, Coal requirement, minimum required payment, year three | 83.8 |  |  |
Coal requirement, minimum required payment, year four | 111.6 |  |  |
PNM | Loss on long-term purchase commitment | San Juan Generating Station |  |  |  |
Other Commitments [Line Items] |  |  |  |
Annual funding post-term reclamation trust | 2.7 | $ 10.0 | $ 5.2 |
PNM | Mine Reclamation Trust | Four Corners |  |  |  |
Other Commitments [Line Items] |  |  |  |
Funds contributed to mine reclamation trust | 0.2 | 2.4 | $ 2.2 |
Funds contributed next fiscal year through year five | 2.1 |  |  |
PNM | Mine Reclamation Trust | San Juan Generating Station And Four Corners |  |  |  |
Other Commitments [Line Items] |  |  |  |
Customer reclamation funding cost, maximum | 100.0 |  |  |
PNM | Surface | Loss on long-term purchase commitment |  |  |  |
Other Commitments [Line Items] |  |  |  |
Liability for interim storage costs | 50.0 | 62.6 |  |
PNM | Underground | Loss on long-term purchase commitment |  |  |  |
Other Commitments [Line Items] |  |  |  |
Liability for interim storage costs | 26.2 | $ 28.2 |  |
PNM | San Juan Generating Station | Surface | Loss on long-term purchase commitment |  |  |  |
Other Commitments [Line Items] |  |  |  |
Estimate of possible loss | 53.6 |  |  |
PNM | San Juan Generating Station | Underground | Loss on long-term purchase commitment |  |  |  |
Other Commitments [Line Items] |  |  |  |
Estimate of possible loss | 30.4 |  |  |
NM Capital | San Juan Generating Station | Coal Supply |  |  |  |
Other Commitments [Line Items] |  |  |  |
Coal mine reclamation bonds to be posted with NMMMD | 118.7 |  |  |
Issuance in letters of credit | $ 30.3 |  |  | $ 30.3

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