Benefit Plans and Other Postretirement Benefits, Defined Contribution Plans (Details) - USD ($)		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
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)		5.54%	5.80%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Pre-65		6.50%	6.50%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Post-65		5.50%	5.50%
Ultimate health care trend assumption rate (as a percent)		4.50%	4.50%
Period until ultimate trend rate is reached (in years)		$ 6	$ 7
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)		5.49%	5.80%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase		4.25%	4.25%
Net benefit cost recognized for financial reporting		$ 4,000,000	$ 8,000,000	8,000,000
Settlement charge	[1]	0	6,000,000	5,000,000
Pension Plan [Member] | NSP Wisconsin [Member]
Defined Benefit Plan Disclosure [Line Items]
Settlement charge			5,000,000	$ 0
Supplemental Executive Retirement Plan (SERP) and Nonqualified Pension Plan | Parent Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Net benefit cost recognized for financial reporting		$ 2,000,000	$ 17,000,000

[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. There were no settlement charges recorded to the qualified pension plans in 2023. In 2022, as a result of lump-sum distributions during the plan years, NSP-Wisconsin recorded a total pension settlement charge of $5 million, of which $1 million was recorded in the income statement.