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MTPSC (Details) - MTPSC - Montana-Dakota Utilities Co. [Member] - Electric - USD ($) $ in Millions | Jun. 12, 2023 | Mar. 15, 2023 | Feb. 01, 2023 | Nov. 04, 2022
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Public Utilities, General Disclosures [Line Items] |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount |  |  |  | $ 10.5
Public Utilities, Requested Rate Increase (Decrease), Percentage |  |  |  | 15.20%
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount | $ 6.1 | $ 11.5 |  |
Public Utilities, Requested Rate Increase (Decrease), Amended, Percentage | 9.10% | 17.00% |  |
Public Utilities, Interim Rate Increase (Decrease), Amount |  |  | $ 1.7 |
Public Utilities, Interim Rate Increase (Decrease), Percentage |  |  | 2.70% |
Public Utilities, Requested Return on Equity, Percentage | 9.65% |  |  |

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