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Jointly-Owned Facilities and Projects (Details) $ in Millions | Dec. 31, 2018 USD ($) MW | Dec. 31, 2017 USD ($)
--- | --- | ---
Jointly-Owned Facilities and Projects [Line Items] |  |
Plant in Service | $ 751.1 | $ 769.2
Accumulated Depreciation | 240.9 | 231.2
Construction Work in Progress | 6.4 | 8.2
Transmission [Member] | CapX2020 Projects [Member] |  |
Jointly-Owned Facilities and Projects [Line Items] |  |
Plant in Service | 101.0 | 101.0
Accumulated Depreciation | 11.0 | 8.4
Construction Work in Progress | $ 0.0 | $ 0.0
Transmission [Member] | CapX2020 Projects [Member] | Minimum [Member] |  |
Jointly-Owned Facilities and Projects [Line Items] |  |
Minnesota Power Ownership % | 9.30% | 9.30%
Transmission [Member] | CapX2020 Projects [Member] | Maximum [Member] |  |
Jointly-Owned Facilities and Projects [Line Items] |  |
Minnesota Power Ownership % | 14.70% | 14.70%
Boswell Unit 4 [Member] | Jointly-Owned Electricity Generation Plant [Member] |  |
Jointly-Owned Facilities and Projects [Line Items] |  |
Minnesota Power Ownership % | 80.00% | 80.00%
Generating Capacity Jointly Owned (MW) | MW | 585 |
Plant in Service | $ 650.1 | $ 668.2
Accumulated Depreciation | 229.9 | 222.8
Construction Work in Progress | $ 6.4 | $ 8.2
Boswell Unit 4 [Member] | Jointly-Owned Electricity Generation Plant [Member] | Minnesota Power [Member] |  |
Jointly-Owned Facilities and Projects [Line Items] |  |
Minnesota Power Ownership % | 80.00% |
Boswell Unit 4 [Member] | Jointly-Owned Electricity Generation Plant [Member] | WPPI Energy [Member] |  |
Jointly-Owned Facilities and Projects [Line Items] |  |
WPPI Energy Ownership % | 20.00% |

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- Definition Jointly-Owned Electric Facility Percentage Not Owned + References No definition available. + Details
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- Definition The period end amount owned by the reporting utility of a jointly owned utility plant in service. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 360 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 10.C) -URI http://asc.fasb.org/extlink&oid=115995737&loc=d3e659983-123033 + Details
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- Definition 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. + References No definition available. + Details
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- Definition The period end amount of construction work in progress at a jointly owned electricity generation plant. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 360 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 10.C) -URI http://asc.fasb.org/extlink&oid=115995737&loc=d3e659983-123033 + Details
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- Definition The period end amount of accumulated depreciation in a jointly owned electricity generation plant. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 360 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 10.C) -URI http://asc.fasb.org/extlink&oid=115995737&loc=d3e659983-123033 + Details
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- Definition The proportionate share of interest (percent) in a jointly owned utility plant. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 360 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 10.C) -URI http://asc.fasb.org/extlink&oid=115995737&loc=d3e659983-123033 + Details
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