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NDPSC (Details 2) - Electricity [Member] - Montana-Dakota Utilities Co. [Member] - NDPSC [Member] - USD ($) | Mar. 01, 2020 | Oct. 28, 2019
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Public Utilities, General Disclosures [Line Items] |  |
Total Transmission Cost Adjustment Rider |  | $ 9,200,000
Public Utilities, Approved Rate Increase (Decrease), Amount |  | $ 600,000
Public utilities, approved rate increase (decrease), percentage |  | 7.20%
Transmission Capital Projects Increase (Decrease) |  | $ 1,500,000
Subsequent Event [Member] |  |
Public Utilities, General Disclosures [Line Items] |  |
Public Utilities, Approved Rate Increase (Decrease), Amount | $ (800,000) |
Renewable Resource Cost Adjustment Rate Tariff | $ 14,700,000 |

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