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Commitments and Contingencies MISO ROE Complaints (Details) - NSP Minnesota and NSP Wisconsin - FERC Proceeding, MISO ROE Complaint [Member] - Federal Energy Regulatory Commission (FERC) [Member] | 1 Months Ended | 6 Months Ended | 39 Months Ended |
--- | --- | --- | --- | ---
Feb. 28, 2015 | Nov. 30, 2013 | Jun. 30, 2017 | Dec. 31, 2019 | Sep. 30, 2020
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Public Utilities, Base Return On Equity Charged To Customers Through Transmission Formula Rates | 12.38% | 12.38% |  |  |
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, Recommended By Third Parties | 8.67% | 9.15% |  |  |
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, Approved |  |  | 10.32% |  |
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, with RTO Adder, Approved |  |  | 10.82% |  |
Public Utilities, ROE developed with new approach |  |  |  | 9.88% |
Public Utilities, ROE developed with new approach, with RTO Adder, Approved |  |  |  | 10.38% |
Public Utilities, ROE New Base, Complaint Number 1 |  |  |  | 10.02% |
Minimum [Member] |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Basis points |  |  |  |  | 50
Maximum [Member] |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Basis points |  |  |  |  | 100

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