Regulatory matters - NDPSC (Details) - Electric Transmission - NDPSC - Subsequent Event - Montana-Dakota Utilities Co. $ in Millions	Jul. 15, 2025 USD ($)
Public Utilities, General Disclosures [Line Items]
Transmission cost adjustment rider, requested revenue recovery	$ 6.3
Public utilities, requested rate increase (decrease), amount	7.2
Capital investment in transmission projects, requested revenue recovery amount	$ 8.6

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