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Regulatory matters - MTPSC (Details) - Natural gas distribution - MTPSC - Montana-Dakota Utilities Co. $ in Millions | Jan. 14, 2025 USD ($) | Oct. 15, 2024 USD ($) | Jul. 15, 2024 USD ($) | Apr. 03, 2025 USD ($)
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Public Utilities, General Disclosures [Line Items] |  |  |  |
Public utilities, requested rate increase (decrease), amount |  | $ 8.0 | $ 9.4 |
Public utilities, requested rate increase (decrease), percentage |  | 10.20% | 11.10% |
Public utilities, interim rate increase (decrease), amount | $ 7.7 |  |  |
Public utilities, annual revenue increase (decrease) |  |  |  | $ 7.3
Public utilities, annual revenue increase (decrease), percentage |  |  |  | 0.086

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