Benefit Plans and Other Postretirement Benefits (Details) $ in Millions	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		$ 24	$ 24	$ 47	$ 48
Interest cost (a)		33	36	67	72
Expected return on plan assets (a)		(52)	(52)	(104)	(104)
Amortization of prior service credit (a)		(1)	0	(2)	(1)
Amortization of net loss (a)		27	26	55	53
Net periodic benefit cost (credit)		31	34	63	68
Costs not recognized due to the effects of regulation		(1)	(4)	(2)	(8)
Net benefit cost (credit) recognized for financial reporting		30	30	61	60
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	1	2
Interest cost (a)		5	6	11	12
Expected return on plan assets (a)		(6)	(6)	(13)	(12)
Amortization of prior service credit (a)		(3)	(3)	(5)	(5)
Amortization of net loss (a)		2	1	3	2
Net periodic benefit cost (credit)		(1)	(1)	(3)	(1)
Costs not recognized due to the effects of regulation		0	0	0	0
Net benefit cost (credit) recognized for financial reporting		$ (1)	$ (1)	$ (3)	$ (1)