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MTPSC (Details 2) - Gas Distribution [Member] - MTPSC [Member] - Montana-Dakota Utilities Co. [Member] - USD ($) $ in Millions	Mar. 15, 2021	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		7.70%
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 7.3
Public Utilities, Approved Rate Increase (Decrease), Percentage	11.40%

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Percentage of public utility's approved rate increase (decrease) by 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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