Jointly-Owned Facilities and Assets (Details) $ in Millions	Dec. 31, 2022 USD ($) MW	Dec. 31, 2021 USD ($)
Jointly-Owned Facilities and Assets [Line Items]
Plant in Service	$ 813.0	$ 783.7
Accumulated Depreciation	361.2	329.6
Construction Work in Progress	3.3	30.1
Transmission [Member] \| Transmission Assets [Member]
Jointly-Owned Facilities and Assets [Line Items]
Plant in Service	101.0	101.0
Accumulated Depreciation	21.1	18.5
Construction Work in Progress	$ 0.0	$ 0.0
Transmission [Member] \| Transmission Assets [Member] \| Minimum [Member]
Jointly-Owned Facilities and Assets [Line Items]
Minnesota Power Ownership %	9.30%	9.30%
Transmission [Member] \| Transmission Assets [Member] \| Maximum [Member]
Jointly-Owned Facilities and Assets [Line Items]
Minnesota Power Ownership %	14.70%	14.70%
Boswell Unit 4 [Member] \| Jointly-Owned Electricity Generation Plant [Member]
Jointly-Owned Facilities and Assets [Line Items]
Minnesota Power Ownership %	80.00%	80.00%
Generating Capacity Jointly Owned (MW) \| MW	585
Plant in Service	$ 712.0	$ 682.7
Accumulated Depreciation	340.1	311.1
Construction Work in Progress	$ 3.3	$ 30.1
Boswell Unit 4 [Member] \| Jointly-Owned Electricity Generation Plant [Member] \| Minnesota Power [Member]
Jointly-Owned Facilities and Assets [Line Items]
Minnesota Power Ownership %	80.00%
Boswell Unit 4 [Member] \| Jointly-Owned Electricity Generation Plant [Member] \| WPPI Energy [Member]
Jointly-Owned Facilities and Assets [Line Items]
WPPI Energy Ownership %	20.00%

Generating Capacity Jointly Owned (MW)

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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 https://asc.fasb.org/extlink&oid=122136288&loc=d3e659983-123033

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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.

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- Definition

The period end amount of construction work in progress at a jointly owned electricity generation plant.

+ References

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- Definition

The period end amount of accumulated depreciation in a jointly owned electricity generation plant.

+ References

+ Details

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- Definition

The proportionate share of interest (percent) in a jointly owned utility plant.

+ References

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