Benefit Plans and Other Postretirement Benefits (Details) - Pension Plan [Member] $ in Millions		1 Months Ended	3 Months Ended
		Jan. 31, 2021 USD ($) Plan	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost			$ 2.0	$ 2.0
Interest cost (a)	[1]		4.0	5.0
Expected return on plan assets (a)	[1]		(7.0)	(7.0)
Amortization of net loss (gain) (a)	[1]		4.0	3.0
Net periodic benefit cost (credit)			$ 3.0	$ 3.0
Contributions to pension plans		$ 14.0
Xcel Energy Inc.
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Contributions to pension plans		$ 125.0
Number of 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 income (expense), net” in the statements of income or capitalized on the balance sheets as a regulatory asset.