Related Party Transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	$ 8	$ 53
Accounts payable	58	44
NSP-Minnesota
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	0	19
Accounts payable	1	0
NSP-Wisconsin
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	0	0
Accounts payable	1	0
SPS
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	0	0
Accounts payable	6	0
Other subsidiaries of Xcel Energy Inc.
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	8	34
Accounts payable	50	44
Other Expense
Operating expenses
Costs and Expenses, Related Party	571	532	$ 519
Other Revenue
Operating revenues
Operating Revenue from Related Parties	$ 5	$ 5	$ 4