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 ($)
Other Postretirement Benefits Plan [Member]
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		$ 152	$ 192
Interest cost		3,749	4,191
Expected return on plan assets		(5,675)	(5,476)
Amortization of prior service credit		(1,545)	(1,562)
Amortization of net loss		1,021	961
Net periodic benefit cost (credit)		(2,298)	(1,694)
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation		0	0
Net benefit cost (credit) recognized for financial reporting		(2,298)	(1,694)
Pension Plan [Member]
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		7,271	6,820
Interest cost		11,814	12,640
Expected return on plan assets		(17,130)	(17,134)
Amortization of prior service credit		(845)	(803)
Amortization of net loss		7,815	7,089
Net periodic benefit cost (credit)		8,925	8,612
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation		1,475	736
Net benefit cost (credit) recognized for financial reporting		$ 10,400	$ 9,348
Total contributions to the pension plans during the period	$ 22,000
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