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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 | 3 Months Ended | 7 Months Ended | 16 Months Ended | 17 Months Ended | 23 Months Ended
--- | --- | --- | --- | --- | --- | ---
Feb. 28, 2015 | Nov. 30, 2013 | Jun. 30, 2017 | Dec. 31, 2020 | Sep. 30, 2021 | Sep. 30, 2021 | Sep. 30, 2021
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |
Public Utilities, Base Return On Equity Charged To Customers Through Transmission Formula Rates | 1238.00% | 1238.00% |  |  |  |  |
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, Recommended By Third Parties | 867.00% | 915.00% |  |  |  |  |
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, Approved |  |  | 1032.00% |  |  |  |
Public Utilities, ROE developed with new approach |  |  |  |  |  |  | 988.00%
Public Utilities, ROE New Base, Complaint Number 1 |  |  |  |  |  | 1002.00% |
Basis Point Reduction |  |  |  |  | 1000.00% |  |
Basis Point Reduction - First Complaint |  |  |  | 100000000.00% |  |  |
Basis Point Reduction - Second Complaint |  |  |  | 100000000.00% |  |  |
Basis Point Reduction - Third Complaint |  |  |  | 200000000.00% |  |  |

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