Benefit Plans and Other Postretirement Benefits, Pension Plan Benefit Obligations, Cash Flows and Benefit Costs (Details) - Pension Plans $ in Thousands		1 Months Ended	12 Months Ended
		Jan. 31, 2016 USD ($) Plan	Dec. 31, 2015 USD ($) Plan	Dec. 31, 2014 USD ($) Plan	Dec. 31, 2013 USD ($) Plan
Defined Benefit Plan Disclosure [Line Items]
Accumulated Benefit Obligation at Dec. 31			$ 3,368,239	$ 3,545,928
Change in Projected Benefit Obligation [Roll Forward]
Obligation at Jan. 1		$ 3,567,927	3,746,752	3,440,704
Service cost			99,311	88,342	$ 96,282
Interest cost			148,524	156,619	140,690
Actuarial (gain) loss			(169,678)	342,826
Benefit payments			(256,982)	(281,739)
Obligation at Dec. 31			3,567,927	3,746,752	3,440,704
Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		$ 2,883,780	3,083,771	3,010,140
Actual return (loss) on plan assets			(33,102)	224,808
Employer contributions			90,093	130,562
Benefit payments			(256,982)	(281,739)
Fair value of plan assets at Dec. 31			2,883,780	3,083,771	$ 3,010,140
Funded Status of Plans at Dec. 31 [Abstract]
Funded status	[1]		(684,147)	(662,981)
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost [Abstract]
Net loss			1,710,097	1,757,935
Prior service (credit) cost			(9,073)	(10,878)
Total			1,701,024	1,747,057
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			105,426	113,432
Noncurrent regulatory assets			1,520,975	1,558,649
Deferred income taxes			29,002	29,143
Net-of-tax accumulated other comprehensive income			45,621	45,833
Total			$ 1,701,024	$ 1,747,057
Significant Assumptions Used to Measure Benefit Obligations [Abstract]
Measurement date			December 31, 2015	December 31, 2014
Discount rate for year-end valuation (as a percent)			4.66%	4.11%
Expected average long-term increase in compensation level (as a percent)			4.00%	3.75%
Mortality table			RP 2014	RP 2014
Cash Flows [Abstract]
Number of pension plans to which contributions were made | Plan			4	4	4
Total contributions to Xcel Energy's pension plans during the period			$ 90,100	$ 130,600	$ 192,400
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost			99,311	88,342	96,282
Interest cost			148,524	156,619	140,690
Expected return on plan assets			(213,890)	(207,205)	(198,452)
Amortization of prior service cost (credit)			(1,805)	(1,746)	5,871
Amortization of net loss			125,152	116,762	144,151
Net periodic benefit cost			157,292	152,772	188,542
Costs not recognized due to regulation			(29,633)	(26,315)	(36,724)
Net benefit cost recognized for financial reporting			$ 127,659	$ 126,457	$ 151,818
Significant Assumptions Used to Measure Costs [Abstract]
Discount rate (as a percent)			4.11%	4.75%	4.00%
Expected average long-term increase in compensation level (as a percent)			3.75%	3.75%	3.75%
Expected average long-term rate of return on assets (as a percent)			7.09%	7.05%	6.88%
Expected average long-term rate of return on assets for next fiscal year (as a percent)			6.87%
Subsequent Event
Cash Flows [Abstract]
Number of pension plans to which contributions were made | Plan		4
Total contributions to Xcel Energy's pension plans during the period		$ 125,000

[1] Amounts are recognized in noncurrent liabilities on Xcel Energy’s consolidated balance sheets.