Related Party Transactions (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating revenues
Electric	$ 8,136	$ 9,271	$ 10,896
Other	4,441	4,441	4,441
Operating expenses
Purchased power	1,331	6,539	7,187
Other operating expenses - paid to Xcel Energy Services Inc.	375,766	316,548	338,889
Interest expense	132	114	112
Interest income	273	122	59
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	19,136	93,544
Accounts payable	45,902	30,001
NSP-Minnesota
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	18,065	23,214
Accounts payable	0	0
NSP-Wisconsin
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	8	71
Accounts payable	0	0
SPS
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	1,056	69
Accounts payable	0	0
Other subsidiaries of Xcel Energy Inc.
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	7	70,190
Accounts payable	$ 45,902	$ 30,001