v3.25.2
Benefit Plans and Other Postretirement Benefits (Details) - USD ($)
$ in Millions
 1 Months Ended 3 Months Ended 6 Months Ended
Jan. 31, 2025
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Components of Net Periodic Benefit Cost [Abstract]          
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement     $ (5.0)    
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement, Recognized in Earnings     1.0    
Pension Plan [Member]          
Components of Net Periodic Benefit Cost [Abstract]          
Service cost   $ 1.0 1.0 $ 2.0 $ 2.0
Interest cost (a) [1]   1.0 1.0 2.0 3.0
Expected return on plan assets (a) [1]   (2.0) (2.0) (4.0) (4.0)
Net periodic benefit cost   0.0 6.0 0.0 7.0
Net benefit cost recognized for financial reporting   1.0 4.0 1.0 5.0
Contributions to pension plans $ 9.0        
Amortization of net loss (a) [1]   0.0 1.0 0.0 1.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement [2]   0.0 5.0 0.0 5.0
Effects of regulation   $ 1.0 $ (2.0) $ 1.0 $ (2.0)
Pension Plan [Member] | Parent Company [Member]          
Components of Net Periodic Benefit Cost [Abstract]          
Contributions to pension plans $ 125.0        
[1] The components of net periodic cost other than the service cost component are included 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.