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Commitments and Contingencies - Coal Supply (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Jun. 30, 2024 | Jun. 30, 2024 | Dec. 31, 2023 | Jan. 31, 2016
PNM | Four Corners CSA |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |
Funds contributed, mine reclamation trust |  | $ 3.2 | $ 0.2 |
Reclamation trust funding, 2025 |  | 1.9 |  |
Reclamation trust funding, year 2026 |  | 2.8 |  |
Coal supply | San Juan Generating Station |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |
Cash used to support bank letter or credit arrangement |  |  |  | $ 30.3
Coal supply | NM Capital | San Juan Generating Station |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |
Requirement to post reclamation bonds | $ 118.7 | 118.7 |  |
Cash used to support bank letter or credit arrangement | 30.3 | 30.3 |  |
Underground | PNM | Loss on long-term purchase commitment |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |
Loss contingency accrual | 48.6 | 48.6 | 26.2 |
Underground | PNM | San Juan Generating Station | Loss on long-term purchase commitment |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |
Estimate of possible loss | 59.7 | 59.7 |  |
Surface | PNM | Loss on long-term purchase commitment |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |
Loss contingency accrual | 39.9 | 39.9 | 50.0 |
Surface | PNM | San Juan Generating Station | Loss on long-term purchase commitment |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |
Estimate of possible loss | 46.5 | 46.5 |  |
San Juan Generating Station |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |
Reclamation costs |  | 20.9 |  |
Regulatory disallowance | 4.5 |  |  |
San Juan Generating Station | PNM | Loss on long-term purchase commitment |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |
Annual funding post-term reclamation trust |  |  | $ 2.7 |
Annual funding post-term reclamation trust, remainder of year |  | 21.5 |  |
Annual funding post-term reclamation trust, year one |  | 3.6 |  |
Annual funding post-term reclamation trust, year two |  | 3.7 |  |
San Juan Generating Station | Underground |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |
Increase in regulatory liabilities | 17.0 |  |  |
San Juan Generating Station | Surface |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |
Increase in regulatory liabilities | 4.0 |  |  |
Decrease in deferred regulatory assets | $ 0.5 |  |  |
Reclamation, maximum collection from customers |  | 100.0 |  |
San Juan Generating Station and Four Corners | PNM | Mine Reclamation Trust |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |
Customer reclamation funding cost |  | $ 100.0 |  |

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