Related Party Transactions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating revenues [Abstract]
Electric	$ 56	$ 0	$ 23
Operating expenses [Abstract]
Purchased power	8,809	8,632	9,614
Other operating expenses - paid to Xcel Energy Services Inc.	188,175	197,134	145,917
Interest expense	189	156	73
Interest income	0	6	$ 3
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	949	1,079
Accounts payable	14,414	29,135
NSP-Minnesota
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	935	1,066
Accounts payable	0	0
NSP-Wisconsin
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	0	0
Accounts payable	333	71
PSCo
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	0	0
Accounts payable	745	414
Other Subsidiaries of Xcel Energy Inc.
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	14	13
Accounts payable	$ 13,336	$ 28,650