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Regulatory Matters - Electric Rates (Details) $ in Millions |  |  |  |  | 3 Months Ended | 4 Months Ended | 8 Months Ended | 12 Months Ended | 18 Months Ended
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jan. 13, 2022 USD ($) | Nov. 01, 2021 USD ($) | Nov. 01, 2019 USD ($) | Dec. 20, 2018 | Jun. 30, 2020 USD ($) | Apr. 30, 2020 USD ($) | Dec. 31, 2020 | Dec. 31, 2021 USD ($) Customers Years | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2019 USD ($)
Cost Recovery Riders [Member] |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |
Alternative Revenue Program, Required Collection Period |  |  |  |  |  |  |  | 2 years |  |  |
MPUC [Member] | Fuel Adjustment Clause Filing [Member] | Minnesota Power [Member] |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |
Forced Outage Costs |  |  |  |  |  |  |  |  |  |  | $ 8.0
Administrative Law Judge Recommended Refund |  |  |  |  |  |  |  | $ 5.0 |  |  |
MPUC [Member] | Fuel Adjustment Clause Filing [Member] | Minnesota Power [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |
Commission Approved Refund | $ 5.0 |  |  |  |  |  |  |  |  |  |
MPUC [Member] | Minnesota Power Land Sales | Minnesota Power [Member] |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |
Estimated Market Value - Reservoir Land to be Sold |  |  |  |  |  |  |  | 100.0 |  |  |
PSCW [Member] | 2018 Wisconsin General Rate Case [Member] | SWL&P [Member] | Retail Customers [Member] |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |
Approved Return on Common Equity |  |  |  | 10.40% |  |  |  |  |  |  |
Approved Equity Ratio |  |  |  | 55.00% |  |  |  |  |  |  |
Electric Rates [Member] | MPUC [Member] | Minnesota Cost Recovery Riders [Member] | Minnesota Power [Member] | Retail Customers [Member] |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Cost Recovery Riders |  |  |  |  |  |  |  | $ 38.9 | $ 29.9 | $ 31.8 |
Electric Rates [Member] | MPUC [Member] | 2020 Minnesota General Rate Review [Member] | Minnesota Power [Member] | Retail Customers [Member] |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |
Requested Average Rate Increase |  |  | 10.60% |  |  |  |  |  |  |  |
Requested Return on Equity |  |  | 10.05% |  |  |  |  |  |  |  |
Requested Equity Ratio |  |  | 53.81% |  |  |  |  |  |  |  |
Annual Additional Revenue Generated from Requested Final Rate Increase |  |  | $ 66.0 |  |  |  |  |  |  |  |
Public Utilities, Interim Rate Increase (Decrease), Amount |  |  |  |  |  | $ 36.1 |  |  |  |  |
Proposed Ongoing Customer Rate Increase |  |  |  |  |  |  | 4.10% |  |  |  |
Public Utilities, Interim Rate Increase (Decrease), Percentage |  |  |  |  |  | 5.80% |  |  |  |  |
Public Utilities Reserve for Interim Rates (Recorded During Period) |  |  |  |  | $ 11.7 |  |  |  |  |  |
Electric Rates [Member] | MPUC [Member] | 2022 Minnesota General Rate Review | Minnesota Power [Member] | Retail Customers [Member] |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  |  |
Public Utilities, Interim Rate Increase (Decrease), Amount |  | 80.0 |  |  |  |  |  |  |  |  |
Electric Rates [Member] | MPUC [Member] | 2022 Minnesota General Rate Review | Minnesota Power [Member] | Residential [Member] |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |
Deferred Interim Rates |  | $ 8.0 |  |  |  |  |  |  |  |  |
Electric Rates [Member] | FERC [Member] | FERC-Approved Wholesale Rates [Member] | Minnesota Power [Member] | Municipal Customers [Member] |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Customers | Customers |  |  |  |  |  |  |  | 15 |  |  |
Notice Required to Terminate (Years) | Years |  |  |  |  |  |  |  | 3 |  |  |
Electric Rates [Member] | FERC [Member] | FERC-Approved Wholesale Rates [Member] | Minnesota Power [Member] | Municipal Customers [Member] | Wholesale Electric Contract (Cost-Based Formula Methodology for Entire Term) [Member] |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Customers | Customers |  |  |  |  |  |  |  | 2 |  |  |
Electric Rates [Member] | FERC [Member] | FERC-Approved Wholesale Rates [Member] | Minnesota Power [Member] | Municipal Customers [Member] | Wholesale Electric Contracts (expire December 2024) [Member] |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Customers | Customers |  |  |  |  |  |  |  | 1 |  |  |
Electric Rates [Member] | FERC [Member] | FERC-Approved Wholesale Rates [Member] | Minnesota Power [Member] | Municipal Customers [Member] | Wholesale Electric Contracts (Through 2029) |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Customers | Customers |  |  |  |  |  |  |  | 13 |  |  |

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