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MTPSC (Details 2) - Electric Rate Proceeding [Member] - MTPSC [Member] - USD ($) $ in Millions	Dec. 21, 2018	Sep. 28, 2018
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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Public Utilities, Approved One-Time Increase (Decrease) to Customers, Amount [Line Items]

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Amount of public utility's requested rate increase (decrease) with regulatory agency.

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Percentage of public utility's requested rate increase (decrease) with regulatory agency.

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