Benefit Plans and Other Postretirement Benefits (Details) $ in Millions		1 Months Ended	3 Months Ended		9 Months Ended
		Jan. 31, 2021 USD ($) Plan	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)
Pension Plan [Member]
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost			$ 3	$ 2	$ 8	$ 7
Interest cost (a)	[1]		3	5	11	13
Expected return on plan assets (a)	[1]		(7)	(7)	(22)	(22)
Amortization of net loss (gain) (a)	[1]		4	3	11	10
Net periodic benefit cost (credit)			3	3	8	8
Contributions to pension plans		$ 14
Effects of regulation			(1)	0	0	2
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)			2	3	8	10
Pension Plan [Member] | Xcel Energy Inc.
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Contributions to pension plans		$ 125
Number of pension plans to which contributions were made | Plan		4
Other Postretirement Benefits Plan [Member]
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost			0	0	0	0
Interest cost (a)	[1]		0	0	0	1
Expected return on plan assets (a)	[1]		0	0	(1)	(1)
Amortization of net loss (gain) (a)	[1]		0	0	0	0
Net periodic benefit cost (credit)			0	0	(1)	0
Effects of regulation			0	0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)			$ 0	$ 0	$ (1)	$ 0

[1] The components of net periodic cost other than the service cost component are included in the line item “Other income (expense), net” in the statements of income or capitalized on the balance sheets as a regulatory asset.