Regulatory Matters - Conservation Improvement Program (Details) - MPUC [Member] - USD ($) $ in Millions	3 Months Ended
Sep. 30, 2018	Jun. 30, 2017
CIP Consolidated Filing [Member] \| Minnesota Power [Member]
Regulatory Matters [Line Items]
Approved Financial Incentive	$ 3.0	$ 5.5
Minimum [Member]
Regulatory Matters [Line Items]
CIP Spending Minimum - Percentage	1.50%

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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