MTPSC (Details 2) - Pending Rate Case [Member] - Gas Distribution [Member] - MTPSC [Member] - Montana-Dakota Utilities Co. [Member] - USD ($) $ in Millions	Feb. 01, 2021	Jun. 22, 2020
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 8.6
Public Utilities, Requested Rate Increase (Decrease), Percentage		13.40%
Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Interim Rate Increase (Decrease), Amount	$ 4.9
Public Utilities, Interim Rate Increase (Decrease), Percentage	8.20%

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Amount of public utility's interim rate increase (decrease) allowed while waiting final decision of regulatory agency.

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Percentage of public utility's interim rate increase (decrease) allowed while waiting final decision of regulatory agency.

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Amount of public utility's requested rate increase (decrease) with regulatory agency.

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Percentage of public utility's requested rate increase (decrease) with regulatory agency.

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