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NDPSC (Details 3) - Gas Distribution [Member] - NDPSC [Member] - Montana-Dakota Utilities Co. [Member] - USD ($)	Jun. 01, 2021	Mar. 31, 2021	Mar. 02, 2021	Jan. 01, 2021	Aug. 26, 2020
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount					$ 9,000,000.0
Public Utilities, Requested Rate Increase (Decrease), Percentage					7.80%
Public Utilities, Interim Rate Increase (Decrease), Amount				$ 6,900,000
Public Utilities, Interim Rate Increase (Decrease), Percentage				6.00%
Generation Resource Recovery Rider			$ 0
Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 6,900,000
Public Utilities, Approved Rate Increase (Decrease), Percentage	6.00%
Pending Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 13,500,000

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