Operations and Significant Accounting Policies - ALLETE Clean Energy Asset Acquisition (Details)	May 03, 2019 MW
Diamond Spring [Member] \| ALLETE Clean Energy [Member]
Business Segments [Line Items]
Generating Capacity Owned (MW)	300

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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