Regulatory Matters - Conservation Improvement Program (Details) - MPUC [Member] - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2017	Dec. 31, 2016
Minimum [Member]
Regulatory Matters [Line Items]
CIP Spending Requirement	1.50%
CIP Annual Filing [Member] \| Minnesota Power [Member]
Regulatory Matters [Line Items]
Financial Incentive	$ 5.5	$ 7.5

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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