Benefit Plans and Other Postretirement Benefits (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Jan. 31, 2017 USD ($) Plan	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Other Postretirement Benefits Plan [Member]
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		$ 192	$ 192	$ 576	$ 576
Interest cost		4,191	4,518	12,573	13,554
Expected return on plan assets		(5,476)	(5,575)	(16,428)	(16,725)
Amortization of prior service credit		(1,562)	(1,562)	(4,686)	(4,686)
Amortization of net loss		961	483	2,883	1,449
Net periodic benefit cost (credit)		(1,694)	(1,944)	(5,082)	(5,832)
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation		0	0	0	0
Net benefit cost (credit) recognized for financial reporting		(1,694)	(1,944)	(5,082)	(5,832)
Pension Plan [Member]
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		6,820	6,487	20,460	19,445
Interest cost		12,639	13,852	37,919	41,554
Expected return on plan assets		(17,134)	(17,692)	(51,402)	(53,076)
Amortization of prior service credit		(803)	(801)	(2,409)	(2,408)
Amortization of net loss		7,089	6,692	21,267	20,078
Net periodic benefit cost (credit)		8,611	8,538	25,835	25,593
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation		736	682	1,898	1,947
Net benefit cost (credit) recognized for financial reporting		$ 9,347	$ 9,220	$ 27,733	$ 27,540
Total contributions to the pension plans during the period	$ 16,800
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