Benefit Plans and Other Postretirement Benefits (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended		6 Months Ended
		Jan. 31, 2024	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Components of Net Periodic Benefit Cost [Abstract]
Operating and maintenance expenses			$ 59	$ 57	$ 115	$ 115
Pension Plan [Member]
Components of Net Periodic Benefit Cost [Abstract]
Service cost			1	1	2	2
Interest cost (a)	[1]		1	2	3	3
Expected return on plan assets (a)	[1]		(2)	(2)	(4)	(4)
Amortization of net loss (a)	[1]		1	0	1	1
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	[2]		5	0	5	0
Net periodic benefit cost			6	1	7	2
Effects of regulation			(2)	0	(2)	0
Net benefit cost recognized for financial reporting			4	$ 1	$ 5	$ 2
Contributions to pension plans		$ 7
Operating and maintenance expenses			$ 1
Pension Plan [Member] | Parent Company [Member]
Components of Net Periodic Benefit Cost [Abstract]
Contributions to pension plans		$ 100

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

[2] A settlement charge is required when the amount of lump-sum distributions during the year is greater than the sum of the service and interest cost components of the annual net periodic pension cost. In the second quarter of 2024, as a result of lump-sum distributions during the 2024 plan year, NSP-Wisconsin recorded a pension settlement charge of $5 million, of which $1 million was recognized in the consolidated statement of income after considering the effects of regulation.