Benefit Plans and Other Postretirement Benefits (Details) $ in Thousands	1 Months Ended	3 Months Ended
	Jan. 31, 2018 USD ($) Plan	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)
Pension Plan [Member]
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		$ 2,430	$ 2,440
Interest cost		4,603	4,928
Expected return on plan assets		(7,082)	(6,971)
Amortization of prior service cost (credit)		(35)	0
Amortization of net loss (gain)		3,517	3,245
Net periodic benefit cost (credit)		3,433	3,642
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation		974	148
Net benefit cost (credit) recognized for financial reporting		4,407	3,790
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		279	219
Interest cost		410	415
Expected return on plan assets		(615)	(589)
Amortization of prior service cost (credit)		(101)	(100)
Amortization of net loss (gain)		(113)	(155)
Net periodic benefit cost (credit)		(140)	(210)
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation		0	0
Net benefit cost (credit) recognized for financial reporting		$ (140)	$ (210)