Related Party Transactions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating revenues [Abstract]
Electric	$ 0	$ 23	$ 1,331
Operating expenses [Abstract]
Purchased power	8,632	9,614	8,136
Other operating expenses - paid to Xcel Energy Services Inc.	197,134	145,917	127,669
Interest expense	156	73	178
Interest income	6	3	$ 0
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	1,079	1,983
Accounts payable	29,135	19,790
NSP-Minnesota
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	1,066	1,983
Accounts payable	0	0
NSP-Wisconsin
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	0	0
Accounts payable	71	31
PSCo
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	0	0
Accounts payable	414	5,803
Other Subsidiaries of Xcel Energy Inc.
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	13	0
Accounts payable	$ 28,650	$ 13,956