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Regulatory matters - SDPUC (Details) - Pending Rate Case - SDPUC - Montana-Dakota Utilities Co. $ in Millions | Jan. 26, 2024 USD ($) | Aug. 15, 2023 USD ($) | Jul. 26, 2024 USD ($)
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Public Utilities, General Disclosures [Line Items] |  |  |
Public utilities, interim rate increase (decrease), amount | $ 2.7 |  |
Public utilities, interim rate increase (decrease), percentage | 15.40% |  |
Subsequent Event |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Public utilities, annual revenue increase (decrease) |  |  | $ 1.4
Public utilities, annual revenue increase (decrease), percentage |  |  | 0.086
Electric |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Public utilities, requested rate increase (decrease), amount |  | $ 3.0 |
Public utilities, requested rate increase (decrease), percentage |  | 17.30% |
Natural gas distribution |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Public utilities, requested rate increase (decrease), amount |  | $ 7.4 |
Public utilities, requested rate increase (decrease), percentage |  | 11.20% |
Natural gas distribution | Subsequent Event |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Public utilities, annual revenue increase (decrease) |  |  | $ 5.4
Public utilities, annual revenue increase (decrease), percentage |  |  | 0.081

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