Related Party Transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating expenses [Abstract]
Interest expense	$ 0	$ 0	$ 1
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	9	4
Accounts payable	17	20
NSP-Minnesota
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	3	4
Accounts payable	0	0
PSCo
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	6	0
Accounts payable	0	0
Other Subsidiaries of Xcel Energy Inc.
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	0	0
Accounts payable	17	20
Other Expense [Member]
Operating expenses [Abstract]
Costs and Expenses, Related Party	$ 200	$ 192	$ 195