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Regulatory matters - WYPSC (Details) - WYPSC - Montana-Dakota Utilities Co. $ in Millions | Jun. 30, 2025 USD ($) | Oct. 31, 2024 USD ($) | May 09, 2025 USD ($)
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Natural gas distribution |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Public utilities, annual revenue increase (decrease) |  |  | $ 2.1
Public utilities, annual revenue increase (decrease), percentage |  |  | 0.117
Natural gas distribution | Pending Rate Case |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Public utilities, requested rate increase (decrease), amount |  | $ 2.6 |
Public utilities, requested rate increase (decrease), percentage |  | 14.00% |
Electric distribution | Pending Rate Case |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Public utilities, requested rate increase (decrease), amount | $ 7.5 |  |
Public utilities, requested rate increase (decrease), percentage | 24.40% |  |

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