Borrowings and Other Financing Instruments Bilateral Credit Agreement (Details) - USD ($) $ in Millions		Dec. 31, 2024	Dec. 31, 2023
Short-term Debt [Line Items]
Amount outstanding at period end		$ 695	$ 785
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	[1]	3,550
Letter of Credit
Short-term Debt [Line Items]
Amount outstanding at period end		42	$ 44
NSP Minnesota | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	[1]	700
NSP Minnesota | Letter of Credit | Bilateral Credit Agreement [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		75
Amount outstanding at period end		$ 74

[1] These credit facilities mature in September 2027.