Benefit Plans and Other Postretirement Benefits, Postretirement Benefit Plan Benefit Obligations, Cash Flows and Benefit Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Funded Status of Plans at Dec. 31 [Abstract]
Noncurrent liabilities	$ (941,002)	$ (936,907)
Postretirement Benefit Plan
Change in Projected Benefit Obligation [Roll Forward]
Obligation at Jan. 1	642,869	731,428
Service cost	2,116	3,457	$ 4,079
Interest cost	25,297	34,028	32,141
Medicare subsidy reimbursements	1,958	1,861
Plan participants' contributions	6,718	7,148
Actuarial (gain) loss	(45,793)	(81,699)
Benefit payments	(48,898)	(53,354)
Obligation at Dec. 31	584,267	642,869	731,428
Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1	475,058	492,036
Actual return (loss) on plan assets	(3,570)	12,083
Plan participants' contributions	6,718	7,148
Employer contributions	18,325	17,145
Benefit payments	(48,898)	(53,354)
Fair value of plan assets at Dec. 31	447,633	475,058	492,036
Funded Status of Plans at Dec. 31 [Abstract]
Funded status	(136,634)	(167,811)
Noncurrent assets	1,820	1,014
Current liabilities	(7,495)	(9,110)
Noncurrent liabilities	(130,959)	(159,715)
Net postretirement amounts recognized on consolidated balance sheets	(136,634)	(167,811)
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost [Abstract]
Net loss	103,039	124,064
Prior service (credit) cost	(64,925)	(75,610)
Total	38,114	48,454
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]
Current regulatory assets	352	285
Noncurrent regulatory assets	50,135	59,697
Current regulatory liabilities	(985)	(892)
Noncurrent regulatory liabilities	(16,916)	(17,216)
Deferred income taxes	2,148	2,559
Net-of-tax accumulated other comprehensive income	3,380	4,021
Total	$ 38,114	$ 48,454
Significant Assumptions Used to Measure Benefit Obligations [Abstract]
Measurement date	12/31/2015	12/31/2014
Discount rate for year-end valuation (as a percent)	4.65%	4.08%
Mortality table	RP 2014	RP 2014
Health care costs trend rate - initial (as a percent)	6.00%	6.50%
Ultimate health care trend assumption rate (as a percent)	4.50%
Period until ultimate trend rate is reached (in years)	3 years
Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rate [Abstract]
One-percent increase in APBO	$ 56,383
One-percent decrease in APBO	(47,972)
One-percent increase in service and interest components	3,113
One-percent decrease in service and interest components	(2,594)
Cash Flows [Abstract]
Total contributions to Xcel Energy's postretirement health care plans during the year	18,300	$ 17,100	17,600
Expected contribution to postretirement health care plans during 2016	12,300
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	2,116	3,457	4,079
Interest cost	25,297	34,028	32,141
Expected return on plan assets	(26,600)	(33,954)	(33,011)
Amortization of transition obligation	0	0	825
Amortization of prior service cost (credit)	(10,686)	(10,688)	(12,501)
Amortization of net loss	5,404	11,740	22,325
Net periodic benefit cost	$ (4,469)	$ 4,583	$ 13,858
Significant Assumptions Used to Measure Costs [Abstract]
Discount rate (as a percent)	4.08%	4.82%	4.10%
Expected average long-term rate of return on assets (as a percent)	5.80%	7.17%	7.11%