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	$ 10	$ 0
Accounts payable	15	19
NSP-Minnesota
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	0	0
Accounts payable	6	8
PSCo
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	1	0
Accounts payable	0	0
Other subsidiaries of Xcel Energy Inc.
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	9	0
Accounts payable	9	11
Purchased Power
Operating expenses
Costs and Expenses, Related Party	379	394	$ 411
Transmission Expense
Operating expenses
Costs and Expenses, Related Party	61	64	63
Natural Gas Purchase for Resale
Operating expenses
Costs and Expenses, Related Party	1	1	0
Other Expense
Operating expenses
Costs and Expenses, Related Party	92	87	87
Electricity, US Regulated
Operating revenues
Revenue from Related Parties	$ 168	$ 177	$ 158