Regulatory Matters - Conservation Improvement Program (CIP) (Details) - MPUC [Member] - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015
Regulatory Matters [Line Items]
CIP Spend Requirement	1.50%
CIP Annual Filing [Member] \| Minnesota Power [Member]
Regulatory Matters [Line Items]
CIP Financial Incentive	$ 7.5	$ 6.2

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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