Benefit Plans and Other Postretirement Benefits (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Jan. 31, 2017 USD ($) Plan	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Pension Plan [Member]
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		$ 2,439	$ 2,440	$ 7,319	$ 7,320
Interest cost		4,928	5,315	14,783	15,945
Expected return on plan assets		(6,971)	(6,901)	(20,913)	(20,703)
Amortization of prior service cost (credit)		0	0	0	0
Amortization of net loss (gain)		3,245	2,997	9,735	8,991
Net periodic benefit cost (credit)		3,641	3,851	10,924	11,553
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation		553	637	1,275	1,353
Net benefit cost (credit) recognized for financial reporting		4,194	4,488	12,199	12,906
Total contributions to the pension plans during the period	$ 23,000
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		219	194	657	582
Interest cost		415	455	1,245	1,365
Expected return on plan assets		(589)	(594)	(1,767)	(1,782)
Amortization of prior service cost (credit)		(100)	(100)	(300)	(300)
Amortization of net loss (gain)		(155)	(146)	(465)	(438)
Net periodic benefit cost (credit)		(210)	(191)	(630)	(573)
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation		0	0	0	0
Net benefit cost (credit) recognized for financial reporting		$ (210)	$ (191)	$ (630)	$ (573)