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 [Abstract]
Service cost		$ 1,195	$ 1,154
Interest cost		1,360	1,554
Expected return on plan assets		(2,256)	(2,295)
Amortization of prior service cost (credit)		(8)	35
Amortization of net loss		1,418	1,462
Defined Benefit Plan Net Benefit Cost (Credit) Recognized Before Regulatory Adjustments		1,709	1,910
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation		221	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		1,930	1,910
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
Interest cost		142	148
Expected return on plan assets		(16)	(8)
Amortization of prior service cost (credit)		(88)	(88)
Amortization of net loss		139	109
Defined Benefit Plan Net Benefit Cost (Credit) Recognized Before Regulatory Adjustments		186	168
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation		0	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		$ 186	$ 168
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