Benefit Plans and Other Postretirement Benefits, Fair Value of Pension Plan Assets (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2024		Dec. 31, 2023	Dec. 31, 2022
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
assets transferred		$ 0		$ 0
Pension Plan [Member]
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets		89	[1]	95	$ 97
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	[2]	(6)		0	(6)
Pension Plan [Member] | NSP Wisconsin [Member]
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]			95
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement					0
Pension Plan [Member] | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	5		28
Pension Plan [Member] | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	22		22
Pension Plan [Member] | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Pension Plan [Member] | Fair Value Measured at Net Asset Value Per Share
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Plan assets at net asset value	[1]	62		45
Pension Plan [Member] | Cash equivalents
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	4		8
Pension Plan [Member] | Cash equivalents | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	4		8
Pension Plan [Member] | Cash equivalents | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Pension Plan [Member] | Cash equivalents | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Pension Plan [Member] | Cash equivalents | Fair Value Measured at Net Asset Value Per Share
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Plan assets at net asset value	[1]	0		0
Pension Plan [Member] | Commingled funds
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	62		64
Pension Plan [Member] | Commingled funds | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		19
Pension Plan [Member] | Commingled funds | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Pension Plan [Member] | Commingled funds | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Pension Plan [Member] | Commingled funds | Fair Value Measured at Net Asset Value Per Share
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Plan assets at net asset value	[1]	62		45
Pension Plan [Member] | Debt Securities [Member]
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	22		22
Pension Plan [Member] | Debt Securities [Member] | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Pension Plan [Member] | Debt Securities [Member] | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	22		22
Pension Plan [Member] | Debt Securities [Member] | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Pension Plan [Member] | Debt Securities [Member] | Fair Value Measured at Net Asset Value Per Share
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Plan assets at net asset value	[1]	0		0
Pension Plan [Member] | Domestic and international equity securities
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	1		1
Pension Plan [Member] | Domestic and international equity securities | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	1		1
Pension Plan [Member] | Domestic and international equity securities | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Pension Plan [Member] | Domestic and international equity securities | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Pension Plan [Member] | Domestic and international equity securities | Fair Value Measured at Net Asset Value Per Share
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Plan assets at net asset value	[1]	0		0
Other Postretirement Benefits Plan [Member]
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets		0		0	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	[2]	$ 0		$ 0	$ 0

[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. 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.