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Regulatory Matters - Narrative (Details) $ in Millions |  |  |  |  |  |  | 12 Months Ended | 36 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 19, 2023 USD ($) | Nov. 01, 2023 USD ($) | Feb. 28, 2023 USD ($) | Feb. 27, 2023 | Dec. 20, 2022 USD ($) | Nov. 01, 2021 USD ($) | Dec. 31, 2023 USD ($) contract customer MW | Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($) | Dec. 31, 2022 USD ($) | Dec. 15, 2023 MW | Oct. 02, 2023 MW | Sep. 30, 2023 USD ($) | Feb. 01, 2021 MW
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets |  |  |  |  |  |  | $ 425.4 | $ 441.0 |  | $ 441.0 |  |  |  |
Regulatory Liabilities |  |  |  |  |  |  | $ 574.0 | 526.1 |  | 526.1 |  |  |  |
Minnesota Power | Solar Generation |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Anticipated generating capacity to be purchased (MW) | MW |  |  |  |  |  |  | 20 |  |  |  |  | 300 |  |
Minnesota Power | Wind Generation |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Anticipated generating capacity to be purchased (MW) | MW |  |  |  |  |  |  |  |  |  |  | 400 |  |  |
Other | Solar Generation |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated investment amount |  |  |  |  |  |  | $ 40.0 |  |  |  |  |  |  |
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% |  |  |  |  |  |  |
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% |  |  |  |  |  |  |
ECO Triennial Filing | MPUC | Minnesota Power |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Conservation improvement program goal, next fiscal year |  |  |  |  |  |  | $ 12.5 |  |  |  |  |  |  |
Energy conservation and optimization plan goal, second fiscal year |  |  |  |  |  |  | 12.7 |  |  |  |  |  |  |
Energy conservation and optimization plan goal, third fiscal year |  |  |  |  |  |  | 12.8 |  |  |  |  |  |  |
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 |  |  |  |  |  |  | 2.2 |  |  |  |  |  |  |
CIP Consolidated Filing | MPUC | Minnesota Power |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue from cost recovery riders |  |  |  |  |  |  |  | 1.9 | $ 2.4 |  |  |  |  |
Electric Rates | Fuel Adjustment Clause 2022 | MPUC | Minnesota Power |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets |  |  |  |  |  |  |  | $ 13.0 |  | $ 13.0 |  |  |  |
Electric Rates | Fuel Adjustment Clause 2023 | MPUC | Minnesota Power |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Liabilities |  |  |  |  |  |  | 15.5 |  |  |  |  |  |  |
Electric Rates | Fuel Adjustment Clause | MPUC | Minnesota Power |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets |  |  |  |  |  |  |  |  | 56.0 |  |  |  |  |
Retail Customers | 2018 Wisconsin General Rate Case | PSCW | SWL&P |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Authorized return on equity |  |  |  |  |  |  |  |  |  | 10.40% |  |  |  |
Return on common equity |  |  |  |  |  |  |  |  |  | 55.00% |  |  |  |
Retail Customers | 2022 Wisconsin General Rate Review | PSCW | SWL&P |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested average rate increase |  |  |  |  |  |  |  | 3.60% |  |  |  |  |  |
Requested return on equity |  |  |  |  |  |  |  | 10.40% |  |  |  |  |  |
Requested equity ratio |  |  |  |  |  |  |  | 55.00% |  |  |  |  |  |
Annual additional revenue generated from requested final rate increase |  |  |  |  |  |  |  | $ 4.3 |  |  |  |  |  |
Additional revenue from base rates |  |  |  |  | $ 3.3 |  |  |  |  |  |  |  |  |
Retail Customers | 2022 Wisconsin General Rate Case | PSCW | SWL&P |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Authorized return on equity |  |  |  |  | 10.00% |  |  |  |  |  |  |  |  |
Return on common equity |  |  |  |  | 55.00% |  |  |  |  |  |  |  |  |
Retail Customers | Electric Rates | Current Cost Recovery Rider | MPUC | Minnesota Power |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue from cost recovery riders |  |  |  |  |  |  | $ 57.0 | 38.8 | $ 38.9 |  |  |  |  |
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% |  |  |  |  |  |  |  |  |  |  |
Return on common equity |  |  | 52.50% |  |  |  |  |  |  |  |  |  |  |
Requested average rate increase |  |  |  |  |  | 18.00% |  |  |  |  |  |  |  |
Requested return on equity |  |  |  |  |  | 10.25% |  |  |  |  |  |  |  |
Requested equity ratio |  |  |  |  |  | 53.81% |  |  |  |  |  |  |  |
Annual additional revenue generated from requested final rate increase |  |  |  |  |  | $ 108.0 |  |  |  |  |  |  |  |
Additional revenue from base rates |  |  | $ 60.0 |  |  |  |  |  |  |  |  |  |  |
Public utility - additional rider revenue |  |  | $ 10.0 |  |  |  |  |  |  |  |  |  |  |
Customer refund |  |  |  |  |  |  |  | $ 18.0 |  | $ 18.0 |  |  | $ 39.0 |
Retail Customers | Electric Rates | 2024 Minnesota General Rate Case | MPUC | Minnesota Power |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested average rate increase |  | 12.00% |  |  |  |  |  |  |  |  |  |  |  |
Requested return on equity |  | 10.30% |  |  |  |  |  |  |  |  |  |  |  |
Requested equity ratio |  | 53.00% |  |  |  |  |  |  |  |  |  |  |  |
Annual additional revenue generated from requested final rate increase | $ 64.0 | $ 89.0 |  |  |  |  |  |  |  |  |  |  |  |
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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