Benefit Plans and Other Postretirement Benefits (Details) $ in Millions	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		$ 24	$ 24
Interest cost (a)		33	36
Expected return on plan assets (a)		(52)	(52)
Amortization of prior service credit (a)		(1)	0
Amortization of net loss (a)		27	26
Net periodic benefit cost (credit)		31	34
Costs not recognized due to the effects of regulation		0	(4)
Net benefit cost (credit) recognized for financial reporting		31	30
Total contributions to Xcel Energy's pension plans during the period	$ 150
Number of pension plans to which contributions were made | Plan	4
Other Postretirement Benefits Plan [Member]
Components of Net Periodic Benefit Cost [Abstract]
Service cost		1	1
Interest cost (a)		5	6
Expected return on plan assets (a)		(6)	(6)
Amortization of prior service credit (a)		(3)	(3)
Amortization of net loss (a)		2	1
Net periodic benefit cost (credit)		(1)	(1)
Costs not recognized due to the effects of regulation		0	0
Net benefit cost (credit) recognized for financial reporting		$ (1)	$ (1)