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MTPSC (Details 2) - Electric Rate Proceeding [Member] - MTPSC [Member] - USD ($) $ in Millions | Dec. 21, 2018 | Sep. 28, 2018
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Public Utilities, General Disclosures [Line Items] |  |
Public utilities, requested rate increase (decrease), amount |  | $ 11.9
Public utilities, requested rate increase (decrease), percentage |  | 18.90%
Tax Cuts and Jobs Act [Member] |  |
Public Utilities, General Disclosures [Line Items] |  |
Public Utilities, Approved One-Time Increase (Decrease) to Customers, Amount | $ (1.5) |

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