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Regulatory Matters - Electric Rates (Details) - USD ($) $ in Millions |  |  | 4 Months Ended | 6 Months Ended |
--- | --- | --- | --- | --- | ---
May 01, 2020 | Nov. 01, 2019 | Apr. 30, 2020 | Jun. 30, 2020 | Jun. 30, 2019 | Dec. 31, 2019
Regulatory Matters [Line Items] |  |  |  |  |  |  |
Public Utilities Reserve for Interim Rates | [1] |  |  |  | $ 11.7 |  | $ 0.0
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 |  |  |  |  | 14.9 | $ 17.4 |
Electric Rates [Member] | MPUC [Member] | 2020 Minnesota General Rate Case [Member] | Minnesota Power [Member] | Retail Customers [Member] |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |
Annual Additional Revenue Generated from Requested Final Rate Increase |  |  | $ 66.0 |  |  |  |
Requested Rate Increase Percent |  |  | 10.60% |  |  |  |
Interim Rate Increase |  |  | $ 36.1 |  |  |  |
Requested Return on Equity |  |  | 10.05% |  |  |  |
Requested Equity Capital Structure |  |  | 53.81% |  |  |  |
Ongoing Customer Rate Increase |  | 4.10% |  |  |  |  |
Public Utilities, Interim Rate Increase (Decrease), Percentage |  |  |  | 5.80% |  |  |
Public Utilities Reserve for Interim Rates |  |  |  |  | $ 11.7 |  |
[1] | Provision for Interim Rate Refund represents reserves for interim rates resulting from the MPUC’s approval of Minnesota Power’s petition and proposal to resolve and withdraw its rate case. (See Note 2. Regulatory Matters.)

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