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Regulatory Matters - Electric Rates (Details) - USD ($) $ in Thousands						3 Months Ended
	May 03, 2024	Apr. 01, 2024	Mar. 29, 2024	Dec. 19, 2023	Nov. 01, 2023	Mar. 31, 2024	Sep. 30, 2023	Mar. 31, 2023	Dec. 31, 2023
Regulatory Matters [Line Items]
Regulatory Assets						$ 409,000			$ 425,400
Regulatory Liabilities						564,000			$ 574,000
ECO Annual Filing Member | MPUC | Minnesota Power
Regulatory Matters [Line Items]
Revenue from cost recovery riders and other regulatory programs							$ 2,200
ECO Annual Filing Member | MPUC | Minnesota Power | Subsequent Event
Regulatory Matters [Line Items]
Revenue from cost recovery riders and other regulatory programs		$ 2,200
Electric Rates | Fuel Adjustment Clause 2023 | MPUC | Minnesota Power
Regulatory Matters [Line Items]
Regulatory Assets						13,000
Retail Customers | Electric Rates | Current Cost Recovery Rider | MPUC | Minnesota Power
Regulatory Matters [Line Items]
Revenue from cost recovery riders and other regulatory programs						8,300		$ 16,400
Retail Customers | Electric Rates | 2024 Minnesota General Rate Case | MPUC | Minnesota Power
Regulatory Matters [Line Items]
Requested rate increase percent					12.00%
Approved rate increase				$ 64,000
Requested return on equity					10.30%
Requested equity capital structure					53.00%
Annual additional revenue generated from requested final rate increase					$ 89,000
Regulatory liabilities						$ 5,500
Retail Customers | Electric Rates | 2024 Minnesota General Rate Case | MPUC | Minnesota Power | Subsequent Event
Regulatory Matters [Line Items]
Requested return on equity	9.78%
Annual additional revenue generated from requested final rate increase	$ 33,970
Retail Customers | Electric Rates | 2024 Wisconsin General Rate Case | PSCW | SWL&P
Regulatory Matters [Line Items]
Requested rate increase percent			5.90%
Requested return on equity			10.00%
Requested equity capital structure			55.00%
Annual additional revenue generated from requested final rate increase			$ 7,300

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