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Regulatory Matters - Narrative (Details) $ in Thousands |  |  |  |  |  |  |  | 3 Months Ended | 12 Months Ended | 36 Months Ended |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
May 03, 2024 USD ($) | Mar. 29, 2024 USD ($) | Dec. 19, 2023 USD ($) | Nov. 01, 2023 USD ($) | Oct. 01, 2023 | Feb. 28, 2023 | Dec. 20, 2022 USD ($) | Mar. 31, 2025 | Dec. 31, 2024 USD ($) contract customer MW | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($) | Dec. 31, 2022 USD ($) | Jan. 30, 2025 MW | Oct. 17, 2024 | Dec. 15, 2023 MW | Oct. 02, 2023 MW | Sep. 30, 2023 USD ($) | Feb. 01, 2021 MW
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory asset |  |  |  |  |  |  |  |  | $ 371,700 | $ 425,400 |  |  |  |  |  |  |  |
Regulatory liability |  |  |  |  |  |  |  |  | 570,500 | 574,000 |  |  |  |  |  |  |  |
Depreciation |  |  |  |  |  |  |  |  | $ 271,300 | 251,700 | $ 242,000 |  |  |  |  |  |  |
ATC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Authorized return on equity |  |  |  |  |  |  |  |  | 10.02% |  |  |  |  |  |  |  |  |
Authorized return on equity, including incentive adder |  |  |  |  |  |  |  |  | 10.52% |  |  |  |  | 10.48% |  |  |  |
Solar Project |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Solar project, generating production (MW) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 119.5 |  |
Minnesota Power | Solar Generation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Solar project, generating production (MW) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 300 |  |
Minnesota Power | Solar Generation | Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Distributed solar project, generating production (MW) | MW |  |  |  |  |  |  |  |  |  |  |  |  | 10 |  |  |  |  |
Minnesota Power | Solar Project |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Solar project, generating production (MW) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 85 |  |
Minnesota Power | Wind Generation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Solar project, generating production (MW) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 400 |  |  |
Minnesota Power | Maximum | Solar Generation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Distributed solar project, generating production (MW) | MW |  |  |  |  |  |  |  |  | 85 |  |  |  |  |  |  |  |  |
Minnesota Power | Minimum | Solar Generation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Distributed solar project, generating production (MW) | MW |  |  |  |  |  |  |  |  | 65 |  |  |  |  |  |  |  |  |
MPUC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Minnesota solar energy standard - overall mandate percentage |  |  |  |  |  |  |  |  | 1.50% |  |  |  |  |  |  |  |  |
MPUC | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cip spending minimum - percentage |  |  |  |  |  |  |  |  | 1.50% |  |  |  |  |  |  |  |  |
Minnesota solar energy standard - overall mandate percentage |  |  |  |  |  |  |  |  | 1.50% |  |  |  |  |  |  |  |  |
Minnesota solar energy standard - small scale solar mandate percentage |  |  |  |  |  |  |  |  | 10.00% |  |  |  |  |  |  |  |  |
Distributed Minnesota solar energy standard - overall mandate percentage |  |  |  |  |  |  |  |  | 3.00% |  |  |  |  |  |  |  |  |
MPUC | Minnesota Power | Solar Generation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Generating capacity (MW) | MW |  |  |  |  |  |  |  |  | 40 |  |  |  |  |  |  |  |  |
FERC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
FERC authorized return on common equity |  |  |  |  |  |  |  |  | 10.02% |  |  |  |  |  |  |  |  |
FERC authorized return on equity including incentive adder |  |  |  |  |  |  |  |  | 10.52% |  |  |  |  |  |  |  |  |
Authorized return on equity |  |  |  |  |  |  |  |  |  |  |  |  |  | 9.98% |  |  |  |
2021 Integrated Resource Plan | MPUC | Maximum | Renewable Generation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Generating capacity (MW) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 700
CIP Consolidated Filing Member | MPUC | Minnesota Power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue from cost recovery riders |  |  |  |  |  |  |  |  | $ 2,200 |  |  |  |  |  |  |  |  |
CIP Consolidated Filing | MPUC | Minnesota Power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue from cost recovery riders |  |  |  |  |  |  |  |  |  | 2,200 | 1,900 |  |  |  |  |  |  |
ECO Triennial Filing | MPUC | Minnesota Power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Conservation improvement program goal, next fiscal year |  |  |  |  |  |  |  |  | 12,700 |  |  |  |  |  |  |  |  |
Energy conservation and optimization plan goal, second fiscal year |  |  |  |  |  |  |  |  | 12,800 |  |  |  |  |  |  |  |  |
Electric Rates | Fuel Adjustment Clause 2022 | MPUC | Minnesota Power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory asset |  |  |  |  |  |  |  |  |  |  | 13,000 | $ 13,000 |  |  |  |  |  |
Electric Rates | Fuel Adjustment Clause 2023 | MPUC | Minnesota Power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability |  |  |  |  |  |  |  |  | 4,500 | 15,500 |  |  |  |  |  |  |  |
Retail Customers | Deferred Accounting Petition | MPUC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Depreciation |  |  |  |  |  |  |  |  | 4,200 |  |  |  |  |  |  |  |  |
Retail Customers | 2018 Wisconsin General Rate Case | PSCW | SWL&P |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested return on equity |  | 10.40% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested equity ratio |  | 55.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Retail Customers | 2022 Wisconsin General Rate Case | PSCW | SWL&P |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Authorized return on equity |  |  |  |  |  |  | 10.00% |  |  |  |  | 10.00% |  |  |  |  |  |
Return on common equity |  |  |  |  |  |  | 55.00% |  |  |  |  | 55.00% |  |  |  |  |  |
Additional revenue from base rates |  |  |  |  |  |  | $ 3,300 |  |  |  |  |  |  |  |  |  |  |
Retail Customers | 2024 Wisconsin General Rate Case | PSCW | SWL&P |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Authorized return on equity |  |  |  |  |  |  |  |  |  |  |  | 9.80% |  |  |  |  |  |
Return on common equity |  |  |  |  |  |  |  |  |  |  |  | 55.00% |  |  |  |  |  |
Requested return on equity |  | 10.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested equity ratio |  | 55.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested average rate increase |  | 5.90% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual additional revenue generated from requested final rate increase |  | $ 7,300 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional revenue from base rates |  | $ 5,500 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Retail Customers | Electric Rates | Current Cost Recovery Rider | MPUC | Minnesota Power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue from cost recovery riders |  |  |  |  |  |  |  |  | 20,000 | $ 57,000 | $ 38,800 |  |  |  |  |  |  |
Retail Customers | Electric Rates | 2016 Minnesota General Rate Review | MPUC | Minnesota Power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Authorized return on equity |  |  |  |  |  |  |  |  |  |  | 9.25% |  |  |  |  |  |  |
Return on common equity |  |  |  |  |  |  |  |  |  |  | 53.81% |  |  |  |  |  |  |
Retail Customers | Electric Rates | 2022 Minnesota General Rate Review | MPUC | Minnesota Power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Authorized return on equity |  |  |  |  | 9.65% | 9.65% |  |  |  |  |  |  |  |  |  |  |  |
Return on common equity |  |  |  |  | 52.50% | 52.50% |  |  |  |  |  |  |  |  |  |  |  |
Customer refund |  |  |  |  |  |  |  |  |  |  | $ 18,000 | $ 18,000 |  |  |  |  | $ 39,000 |
Retail Customers | Electric Rates | 2024 Minnesota General Rate Case | MPUC | Minnesota Power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested return on equity | 9.78% |  |  | 10.30% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested equity ratio | 53.00% |  |  | 53.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested average rate increase |  |  |  | 12.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual additional revenue generated from requested final rate increase | $ 33,970 |  | $ 64,000 | $ 89,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities |  |  |  |  |  |  |  |  | $ 23,000 |  |  |  |  |  |  |  |  |
Retail Customers | Electric Rates | 2024 Minnesota General Rate Case | MPUC | Minnesota Power | Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested return on equity |  |  |  |  |  |  |  | 9.78% |  |  |  |  |  |  |  |  |  |
Requested equity ratio |  |  |  |  |  |  |  | 53.00% |  |  |  |  |  |  |  |  |  |
Municipal Customers | Electric Rates | FERC-Approved Wholesale Rates | FERC | Minnesota Power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of customers | customer |  |  |  |  |  |  |  |  | 14 |  |  |  |  |  |  |  |  |
Notice required to terminate |  |  |  |  |  |  |  |  | 3 years |  |  |  |  |  |  |  |  |
Municipal Customers | Electric Rates | FERC-Approved Wholesale Rates | FERC | Minnesota Power | Wholesale Electric Contract (Cost-Based Formula Methodology for Entire Term) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of customers | contract |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |
Municipal Customers | Electric Rates | FERC-Approved Wholesale Rates | FERC | Minnesota Power | Wholesale Electric Contracts (Through 2029) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of customers | customer |  |  |  |  |  |  |  |  | 13 |  |  |  |  |  |  |  |  |

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- Definition Minnesota Next Generation Act of 2007 introduced a spend goal of 1.5% of net gross operating revenues from service provided in the state on energy CIPs each year. + References No definition available. + Details
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- Definition Distributed Solar Energy Standard Mandate, Overall Mandate Percentage + References No definition available. + Details
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- Definition The approved percentage return on common equity dedicated to the utility plant in the investee accounted for under the equity method of accounting. + References No definition available. + Details
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- Definition The approved percentage return on common equity, including an incentive adder for participation in a regional transmission organization dedicated to the utility plant in the investee accounted for under the equity method of accounting. + References No definition available. + Details
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- Definition Minnesota's solar energy mandate for total retail electric sales, excluding sales to certain industrial customers, by the end of 2020. + References No definition available. + Details
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- Definition Minnesota's solar energy mandate for small scale solar with photovoltaic devices with a nameplate capacity of 20 kilowatts or less by the end of 2020. Expressed as a percentage of the overall mandate. + References No definition available. + Details
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- Definition Percentage of public utility's requested equity to capital, including debt and equity. + References No definition available. + Details
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