MISO ROE Complaints (Details) - Federal Energy Regulatory Commission (FERC)	1 Months Ended		3 Months Ended	7 Months Ended	10 Months Ended	11 Months Ended	17 Months Ended
	Feb. 28, 2015	Nov. 30, 2013	Mar. 31, 2017	Dec. 31, 2020	Mar. 31, 2021	Mar. 31, 2021	Mar. 31, 2021	Jun. 30, 2021
NSP Minnesota and NSP Wisconsin [Member] [Member] | FERC Proceeding, MISO ROE Complaint
Rate Matters [Abstract]
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 developed with new approach							9.88%
Public Utilities, ROE New Base, Complaint Number 1						10.02%
Basis Point Reduction - Third Complaint				200000000.00%
Basis Point Reduction - Second Complaint				100000000.00%
Basis Point Reduction - First Complaint				100000000.00%
Basis Point Reduction					1000.00%
NSP Minnesota, NSP Wisconsin and SPS
Rate Matters [Abstract]
ROE incentive adders related to FERC NOPR								0.50%