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 [Abstract]
Service cost		$ 1,194	$ 1,155	$ 2,389	$ 2,309
Interest cost		1,360	1,555	2,720	3,109
Expected return on plan assets		(2,257)	(2,295)	(4,513)	(4,590)
Amortization of prior service cost (credit)		(6)	34	(14)	69
Amortization of net loss		1,419	1,461	2,837	2,923
Defined Benefit Plan Net Benefit Cost (Credit) Recognized Before Regulatory Adjustments		1,710	1,910	3,419	3,820
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation		0	0	221	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		1,710	1,910	3,640	3,820
Total contributions to the pension plans during the period	$ 10,000
Other Postretirement Benefits Plan [Member]
Components of Net Periodic Benefit Cost [Abstract]
Service cost		9	7	18	14
Interest cost		142	148	284	296
Expected return on plan assets		(16)	(8)	(32)	(16)
Amortization of prior service cost (credit)		(88)	(88)	(176)	(176)
Amortization of net loss		139	109	278	218
Defined Benefit Plan Net Benefit Cost (Credit) Recognized Before Regulatory Adjustments		186	168	372	336
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation		0	0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		$ 186	$ 168	$ 372	$ 336
Xcel Energy Inc. | Pension Plan [Member]
Components of Net Periodic Benefit Cost [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