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Jointly-Owned Facilities and Assets - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) MW	Dec. 31, 2022
Boswell Unit 4 | Boswell Unit 4
Jointly-Owned Facilities and Assets [Line Items]
% Ownership	80.00%	80.00%
Generating capacity jointly owned (MW) | MW	585
Boswell Unit 4 | Boswell Unit 4 | Minnesota Power
Jointly-Owned Facilities and Assets [Line Items]
% Ownership	80.00%
Boswell Unit 4 | Boswell Unit 4 | WPPI Energy
Jointly-Owned Facilities and Assets [Line Items]
WPPI Energy ownership	20.00%
Nemadji Trail Energy Center
Jointly-Owned Facilities and Assets [Line Items]
Estimated capital expenditures, including past expenditures | $	$ 700
Nemadji Trail Energy Center | Natural Gas-Fired
Jointly-Owned Facilities and Assets [Line Items]
Generating capacity jointly owned (MW) | MW	600
Nemadji Trail Energy Center | South Shore Energy
Jointly-Owned Facilities and Assets [Line Items]
Capital cost spent to date | $	$ 9
Nemadji Trail Energy Center | South Shore Energy | Natural Gas-Fired
Jointly-Owned Facilities and Assets [Line Items]
Expected output entitlement	20.00%

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Generating Capacity Jointly Owned (MW)

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Jointly-Owned Electric Facility Percentage Not Owned

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 980
-SubTopic 360
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 10.C)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479960/980-360-S99-1

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Share of plant output being purchased under a long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 980
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 10.D)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480114/980-10-S99-1

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