Commitments, Guarantees and Contingencies - Power Purchase Agreements (Details) - Square Butte PPA [Member] - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2023	Jun. 30, 2022
Square Butte [Member]
Power Purchase Agreements [Line Items]
PPA Counterparty Total Debt Outstanding	$ 182.4
Square Butte [Member] \| Minnesota Power [Member]
Power Purchase Agreements [Line Items]
Cost of Power Purchased	44.0	$ 41.0
Pro Rata Share of PPA Counterparty Interest Expense	$ 2.7	$ 2.6
Square Butte [Member] \| Minnesota Power [Member] \| Square Butte Coal-fired Unit [Member]
Power Purchase Agreements [Line Items]
Expected Output Entitlement	50.00%
Minnkota Power [Member] \| Minnesota Power [Member] \| Square Butte Coal-fired Unit [Member] \| Minnkota Power PSA [Member]
Power Purchase Agreements [Line Items]
Expected Output Entitlement	37.00%	32.00%

Under long-term contracts with public utility districts, cooperatives or other organizations, a utility company receives a portion of the output of a production plant constructed and financed by the district or cooperative. The utility has only a nominal or no investment at all in the plant but pays a proportionate part of the plant's costs, including debt service.

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- Definition

The allocable portion of interest included in charges under a long-term contract to purchase electric power.

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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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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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- Definition

Amount of operating expense for purchased power procured under arrangements extending beyond one year or the normal operating cycle, if longer, by regulated operation.

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