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NDPSC (Details 3) - NDPSC [Member] - Montana-Dakota Utilities Co. [Member] - USD ($) $ in Millions | Jul. 15, 2021 | Jun. 01, 2021
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Gas Distribution [Member] |  |
Public Utilities, General Disclosures [Line Items] |  |
Public Utilities, Approved Rate Increase (Decrease), Amount |  | $ 13.5
Pending Rate Case [Member] | Electric | Subsequent Event [Member] |  |
Public Utilities, General Disclosures [Line Items] |  |
Total Transmission Cost Adjustment Rider | $ 14.5 |
Public Utilities, Requested Rate Increase (Decrease), Amount | (1.1) |
Transmission Capital Projects Increase (Decrease) | $ 5.1 |

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