Benefit Plans and Other Postretirement Benefits, Postretirement Benefit Plan Benefit Obligations, Cash Flows and Benefit Costs (Details) - USD ($)		1 Months Ended		12 Months Ended
		Jan. 31, 2024		Dec. 31, 2023		Dec. 31, 2022	Dec. 31, 2021
Funded Status of Plans at Dec. 31 [Abstract]
Noncurrent liabilities				$ (27,000,000)		$ (23,000,000)
Pension Plan [Member]
Change in Projected Benefit Obligation [Roll Forward]
Obligation at Jan. 1		$ 112,000,000		112,000,000		141,000,000
Service cost				4,000,000		5,000,000	$ 5,000,000
Interest cost				6,000,000		4,000,000	4,000,000
Actuarial loss				1,000,000		(21,000,000)
Benefit payments				(11,000,000)		(17,000,000)
Obligation at Dec. 31				112,000,000		112,000,000	141,000,000
Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		95,000,000	[1]	97,000,000		137,000,000
Actual return (loss) on plan assets				5,000,000		(24,000,000)
Employer contributions				4,000,000		1,000,000
Benefit payments				(11,000,000)		(17,000,000)
Fair value of plan assets at Dec. 31				95,000,000	[1]	97,000,000	137,000,000
Funded Status of Plans at Dec. 31 [Abstract]
Funded status				(17,000,000)		(15,000,000)
Current liabilities				0		0
Noncurrent liabilities				(17,000,000)		(15,000,000)
Net postretirement amounts recognized on consolidated balance sheets				(17,000,000)		(15,000,000)
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost [Abstract]
Net loss				48,000,000		45,000,000
Prior service (credit) cost				0		0
Total				48,000,000		45,000,000
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]
Current regulatory assets				2,000,000		1,000,000
Noncurrent regulatory assets				46,000,000		44,000,000
Total				$ 48,000,000		$ 45,000,000
Significant Assumptions Used to Measure Benefit Obligations [Abstract]
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%
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost				$ 4,000,000		$ 5,000,000	5,000,000
Interest cost				6,000,000		4,000,000	4,000,000
Expected return on plan assets				(8,000,000)		(8,000,000)	(8,000,000)
Amortization of net loss				2,000,000		3,000,000	5,000,000
Settlement charge	[2]			0		6,000,000	5,000,000
Net periodic benefit cost				$ 4,000,000		$ 10,000,000	$ 11,000,000
Significant Assumptions Used to Measure Costs [Abstract]
Discount rate (as a percent)				5.80%		3.08%	2.71%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase				4.25%		3.75%	3.75%
Expected average long-term rate of return on assets (as a percent)				7.25%		6.60%	6.60%
Defined Benefit Plan Credits (Costs) Not Recognized Due To Effects of Regulation				$ 0		$ (2,000,000)	$ (3,000,000)
Net benefit cost recognized for financial reporting				4,000,000		8,000,000	8,000,000
Other Postretirement Benefits Plan [Member]
Change in Projected Benefit Obligation [Roll Forward]
Obligation at Jan. 1		8,000,000		8,000,000		11,000,000
Service cost				0		0	0
Interest cost				1,000,000		1,000,000	1,000,000
Actuarial loss				0		(3,000,000)
Benefit payments				(1,000,000)		(1,000,000)
Obligation at Dec. 31				8,000,000		8,000,000	11,000,000
Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		0		0		0
Actual return (loss) on plan assets				0		0
Employer contributions				1,000,000		1,000,000
Benefit payments				(1,000,000)		(1,000,000)
Fair value of plan assets at Dec. 31				0		0	0
Funded Status of Plans at Dec. 31 [Abstract]
Funded status				(8,000,000)		(8,000,000)
Current liabilities				(1,000,000)		0
Noncurrent liabilities				(7,000,000)		(8,000,000)
Net postretirement amounts recognized on consolidated balance sheets				(8,000,000)		(8,000,000)
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost [Abstract]
Net loss				3,000,000		4,000,000
Prior service (credit) cost				0		0
Total				3,000,000		4,000,000
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]
Current regulatory assets						0
Noncurrent regulatory assets				3,000,000		4,000,000
Total				$ 3,000,000		$ 4,000,000
Significant Assumptions Used to Measure Benefit Obligations [Abstract]
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
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost				0		0	0
Interest cost				1,000,000		1,000,000	1,000,000
Expected return on plan assets				0		0	0
Amortization of net loss				0		0	0
Settlement charge	[2]			0		0	0
Net periodic benefit cost				$ 1,000,000		$ 1,000,000	$ 1,000,000
Significant Assumptions Used to Measure Costs [Abstract]
Discount rate (as a percent)				5.80%		3.09%	2.65%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase				0.00%		0.00%	0.00%
Expected average long-term rate of return on assets (as a percent)				5.00%		4.10%	4.10%
Defined Benefit Plan Credits (Costs) Not Recognized Due To Effects of Regulation				$ 0			$ 0
Net benefit cost recognized for financial reporting				$ 1,000,000		$ 1,000,000	$ 1,000,000
Subsequent Event | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Payment for Pension Benefits		$ 100,000,000

[1] See Note 8 for further information on fair value measurement inputs and methods.

[2] 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.