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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
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Feb. 28, 2015 | Nov. 30, 2013
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%

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- Definition Percentage of public utility's requested base return on equity charged to customers through transmission formula rates filed with regulatory agency. + References No definition available. + Details
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