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Regulatory matters - NDPSC (Details) - NDPSC - Montana-Dakota Utilities Co. $ in Millions | Nov. 01, 2024 USD ($) | Dec. 13, 2023 USD ($) | Nov. 01, 2023 USD ($) | Sep. 16, 2024 USD ($)
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Public Utilities, General Disclosures [Line Items] |  |  |  |
Public utilities, annual revenue increase (decrease) |  |  |  | $ 9.4
Public utilities, annual revenue increase (decrease), percentage |  |  |  | 0.061
Natural gas distribution | Pending Rate Case |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Public utilities, requested rate increase (decrease), amount |  |  | $ 11.6 |
Public utilities, requested rate increase (decrease), percentage |  |  | 7.50% |
Public utilities, interim rate increase (decrease), amount |  | $ 10.1 |  |
Public utilities, interim rate increase (decrease), percentage |  | 6.50% |  |
Electric | Subsequent Event |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Requested renewable resource cost adjustment rate tariff | $ 18.3 |  |  |
Public utilities, approved rate increase (decrease), amount | $ 2.8 |  |  |

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