Benefit Plans and Other Postretirement Benefits, Postretirement Benefit Plan Benefit Obligations, Cash Flows and Benefit Costs (Details) (Postretirement Benefit Plan [Member], USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Change in Projected Benefit Obligation [Roll Forward]
Obligation at Jan. 1	$ 55,165,000		$ 50,582,000
Service cost	1,259,000		1,092,000		951,000
Interest cost	2,831,000		2,722,000		2,899,000
Medicare subsidy reimbursements	404,000		404,000
Early Retiree Reinsurance Program proceeds shared with retirees	0		260,000
Plan amendments	(4,334,000)		0
Plan participants' contributions	2,004,000		2,315,000
Actuarial loss	7,120,000		4,065,000
Benefit payments	(5,189,000)		(6,275,000)
Obligation at Dec. 31	59,260,000		55,165,000		50,582,000
Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1	39,679,000		39,946,000
Actual return on plan assets	5,375,000		61,000
Plan participants' contributions	2,004,000		2,315,000
Employer contributions	4,353,000		3,632,000
Benefit payments	(5,189,000)		(6,275,000)
Fair value of plan assets at Dec. 31	46,222,000		39,679,000		39,946,000
Funded Status of Plans at Dec. 31 [Abstract]
Funded status	(13,038,000)	[1]	(15,486,000)	[1]
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost [Abstract]
Net loss	(90,000)		(3,281,000)
Prior service credit	(4,317,000)		(131,000)
Transition obligation	0		1,545,000
Total	(4,407,000)		(1,867,000)
Amounts Related to the Funded Status of the Plans Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]
Current regulatory liabilities	(954,000)		(1,867,000)
Noncurrent regulatory liabilities	(3,453,000)		0
Total	(4,407,000)		(1,867,000)
Significant Assumptions Used to Measure Benefit Obligations [Abstract]
Measurement date	2012-12-31		2011-12-31
Discount rate for year-end valuation (in hundredths)	4.10%		5.00%
Mortality table	RP 2000		RP 2000
Health care costs trend rate - initial (in hundredths)	7.50%		6.31%
Ultimate health care trend assumption rate (in hundredths)	4.50%		5.00%
Period until ultimate trend rate is reached (in years)	7 years
Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rate [Abstract]
1-percent increase in APBO	5,220,000
1-percent decrease in APBO	(4,196,000)
1-percent increase in service and interest components	472,000
1-percent decrease in service and interest components	(380,000)
Cash Flows [Abstract]
Total contributions to Xcel Energy's postretirement health care plans during the year	4,400,000		3,600,000
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	1,259,000		1,092,000		951,000
Interest cost	2,831,000		2,722,000		2,899,000
Expected return on plan assets	(2,701,000)		(3,006,000)		(2,639,000)
Amortization of transition obligation	1,545,000		1,669,000		1,669,000
Amortization of prior service cost	(148,000)		(51,000)		(51,000)
Amortization of net loss	1,256,000		855,000		772,000
Net periodic benefit cost	4,042,000		3,281,000		3,601,000
Significant Assumptions Used to Measure Costs [Abstract]
Discount rate (in hundredths)	5.00%		5.50%		6.00%
Expected average long-term rate of return on assets (in hundredths)	6.75%		7.50%		7.50%
Xcel Energy Inc. [Member]
Cash Flows [Abstract]
Total contributions to Xcel Energy's postretirement health care plans during the year	47,100,000		49,000,000
Expected contribution to postretirement health care plans during 2013	$ 21,800,000

[1] Amounts are recognized in noncurrent liabilities on SPS' balance sheet.