Benefit Plans and Other Postretirement Benefits, Defined Contribution Plans (Details) - USD ($)		12 Months Ended
		Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Administrative Expense		$ 2,000,000	$ 2,000,000	$ 2,000,000
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for year-end valuation (as a percent)		5.88%	5.54%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Pre-65		7.00%	6.50%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Post-65		7.50%	5.50%
Ultimate health care trend assumption rate (as a percent)		4.50%	4.50%
Period until ultimate trend rate is reached (in years)		$ 9	$ 6
Net benefit cost recognized for financial reporting		1,000,000	1,000,000	1,000,000
Settlement charge	[1]	$ 0	$ 0	0
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for year-end valuation (as a percent)		5.88%	5.49%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase		4.25%	4.25%
Net benefit cost recognized for financial reporting		$ 8,000,000	$ 4,000,000	8,000,000
Settlement charge	[1]	$ 6,000,000	$ 0	6,000,000
Pension Plan [Member] | NSP Wisconsin [Member]
Defined Benefit Plan Disclosure [Line Items]
Settlement charge				$ 0

[1] A settlement charge is required when the amount of all 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 2024 and 2022, as a result of lump-sum distributions during the plan years, NSP-Wisconsin recorded a total pension settlement charge of $6 million, of which $1 million was recorded in the income statement. There were no settlement charges recorded to the qualified pension plans in 2023.