MISO ROE Complaints (Details) - NSP Minnesota and NSP Wisconsin [Member] [Member] - FERC Proceeding, MISO ROE Complaint - Federal Energy Regulatory Commission (FERC)	1 Months Ended		6 Months Ended	39 Months Ended
	Feb. 28, 2015	Nov. 30, 2013	Jun. 30, 2017	Dec. 31, 2019	Sep. 30, 2020
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 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%
Maximum [Member]
Rate Matters [Abstract]
basis points					100
Minimum [Member]
Rate Matters [Abstract]
basis points					50