Benefit Plans and Other Postretirement Benefits (Details) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Jan. 31, 2018 USD ($) Plan	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)
Pension Plan [Member]
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		$ 2,430	$ 2,440	$ 4,860	$ 4,880
Interest cost		4,602	4,927	9,205	9,855
Expected return on plan assets		(7,082)	(6,971)	(14,164)	(13,942)
Amortization of prior service cost (credit)		(34)	0	(69)	0
Amortization of net loss (gain)		3,517	3,245	7,034	6,490
Net periodic benefit cost (credit)		3,433	3,641	6,866	7,283
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation		761	574	1,735	722
Net benefit cost (credit) recognized for financial reporting		4,194	4,215	8,601	8,005
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	559	438
Interest cost		411	415	821	830
Expected return on plan assets		(616)	(589)	(1,231)	(1,178)
Amortization of prior service cost (credit)		(100)	(100)	(201)	(200)
Amortization of net loss (gain)		(113)	(155)	(226)	(310)
Net periodic benefit cost (credit)		(138)	(210)	(278)	(420)
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation		0	0	0	0
Net benefit cost (credit) recognized for financial reporting		$ (138)	$ (210)	$ (278)	$ (420)