Benefit Plans and Other Postretirement Benefits, Pension Plan Benefit Obligations, Cash Flows and Benefit Costs (Details) $ in Millions		1 Months Ended	12 Months Ended
		Jan. 31, 2018 USD ($) Plan	Dec. 31, 2017 USD ($) Plan	Dec. 31, 2016 USD ($) Plan	Dec. 31, 2015 USD ($) Plan
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Settlement Charge Recognized in Operating and Maintenance Expenses			$ 2,303	$ 2,326	$ 2,330
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated Benefit Obligation at Dec. 31			3,612	3,489
Change in Projected Benefit Obligation [Roll Forward]
Obligation at Jan. 1		$ 3,828	3,682	3,568
Service cost			94	92	99
Interest cost			147	160	149
Plan amendments			(13)	2
Actuarial loss			259	186
Benefit payments	[1]		(341)	(326)
Obligation at Dec. 31			3,828	3,682	3,568
Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		$ 3,088	2,856	2,884
Actual return (loss) on plan assets			411	172
Employer contributions			162	125
Benefit payments	[1]		(341)	(325)
Fair value of plan assets at Dec. 31			3,088	2,856	$ 2,884
Defined Benefit Plan, Plan Assets, Payment for Settlement			174
Funded Status of Plans at Dec. 31 [Abstract]
Funded status	[2]		(740)	(826)
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost [Abstract]
Net loss			1,709	1,836
Prior service (credit) cost			(25)	(5)
Total			1,684	1,831
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			100	101
Noncurrent regulatory assets			1,511	1,650
Deferred income taxes			19	31
Net-of-tax accumulated other comprehensive income			54	49
Total			$ 1,684	$ 1,831
Significant Assumptions Used to Measure Benefit Obligations [Abstract]
Discount rate for year-end valuation (as a percent)			3.63%	4.13%
Expected average long-term increase in compensation level (as a percent)			3.75%	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			$ 162	$ 125	$ 90
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost			94	92	99
Interest cost			147	160	149
Expected return on plan assets			(209)	(210)	(214)
Amortization of prior service cost (credit)			(2)	(2)	(2)
Amortization of net loss			107	97	125
Settlement charge	[3]		81	0	0
Net periodic benefit cost			218	137	157
Costs not recognized due to regulation			(79)	(15)	(29)
Net benefit cost recognized for financial reporting			139	$ 122	$ 128
Settlement Charge Recognized in Operating and Maintenance Expenses			$ 8
Significant Assumptions Used to Measure Costs [Abstract]
Discount rate (as a percent)			4.13%	4.66%	4.11%
Expected average long-term increase in compensation level (as a percent)			3.75%	4.00%	3.75%
Expected average long-term rate of return on assets (as a percent)			6.87%	6.87%	7.09%
Expected average long-term rate of return on assets for next fiscal year (as a percent)			6.87%
Subsequent Event | Pension Plan [Member]
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		$ 150

[1] 2017 amount includes approximately $174 million of lump-sum benefit payments used in the determination of a settlement charge.

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

[3] A settlement charge is required when the amount of all lump-sum distributions during the year is greater than the sum of the service and interest cost components of the annual net periodic pension cost. In the fourth quarter of 2017 as a result of lump-sum distributions during the 2017 plan year, Xcel Energy recorded a total pension settlement charge of $81 million, the majority of which was not recognized due to the effects of regulation. A total of $8 million of that amount was recorded in O&M expenses in the fourth quarter of 2017.