Benefit Plans and Other Postretirement Benefits (Details) - Pension Plan [Member] $ in Millions		1 Months Ended	3 Months Ended		6 Months Ended
		Jan. 31, 2021 USD ($) Plan	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)
Components of Net Periodic Benefit Cost [Abstract]
Service cost			$ 1	$ 1	$ 3	$ 2
Interest cost (a)	[1]		1	1	2	2
Expected return on plan assets (a)	[1]		(2)	(2)	(4)	(4)
Amortization of net loss (a)	[1]		1	1	2	3
Net periodic benefit cost			1	1	3	3
Effects of regulation			0	2	0	4
Net benefit cost recognized for financial reporting			$ 1	$ 3	$ 3	$ 7
Contributions to pension plans		$ 5
Parent Company [Member]
Components of Net Periodic Benefit Cost [Abstract]
Contributions to pension plans		$ 125
Number of Xcel Energy's pension plans to which contributions were made | Plan		4

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