Benefit Plans and Other Postretirement Benefits (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Jan. 31, 2018 USD ($) Plan	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)		Sep. 30, 2017 USD ($)
Pension Plan [Member]
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		$ 2,429	$ 2,439	$ 7,289		$ 7,319
Interest cost		4,603	4,928	13,808	[1]	14,783	[1]
Expected return on plan assets		(7,082)	(6,971)	(21,246)	[1]	(20,913)	[1]
Amortization of prior service cost (credit)		(34)	0	(103)	[1]	0	[1]
Amortization of net loss (gain)		3,517	3,245	10,551	[1]	9,735	[1]
Net periodic benefit cost (credit)		3,433	3,641	10,299		10,924
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation		(468)	553	1,267		1,275
Net benefit cost (credit) recognized for financial reporting		2,965	4,194	11,566		12,199
Total contributions to the pension plans during the period	$ 8,000
Pension Plan [Member] | Xcel Energy Inc.
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Total contributions to the pension plans during the period	$ 150,000
Number of Xcel Energy's pension plans to which contributions were made | Plan	4
Other Postretirement Benefits Plan [Member]
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		280	219	839		657
Interest cost		410	415	1,231	[1]	1,245	[1]
Expected return on plan assets		(615)	(589)	(1,846)	[1]	(1,767)	[1]
Amortization of prior service cost (credit)		(101)	(100)	(302)	[1]	(300)	[1]
Amortization of net loss (gain)		(114)	(155)	(340)	[1]	(465)	[1]
Net periodic benefit cost (credit)		(140)	(210)	(418)		(630)
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation		0	0	0		0
Net benefit cost (credit) recognized for financial reporting		$ (140)	$ (210)	$ (418)		$ (630)

[1] The components of net periodic cost other than the service cost component are included in the line item “other expense, net” in the income statement or capitalized on the balance sheet as a regulatory asset.