XML 117 R99.htm IDEA: XBRL DOCUMENT v3.24.0.1
Pension and Other Postretirement Benefits (Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]      
COVID-19 related regulatory asset $ 2,460.2 $ 2,580.8  
Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Accumulated Benefit Obligation 1,390.9 1,416.8  
Funded status of plan (25.0) 4.6  
Employer contributions 3.1 2.7  
Settlement loss 9.2 12.4 $ 11.4
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement   $ 5.7  
Expected contribution $ 2.2    
Expected return on plan assets 7.00% 4.80% 5.20%
Other Postretirement Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Funded status of plan $ 232.3 $ 224.1  
Employer contributions 23.4 21.3  
Settlement loss 0.0 $ 0.0 $ 0.0
Expected contribution $ 23.1    
Expected return on plan assets 6.96% 5.72% 5.50%
Unrecognized Pension Benefit And Other Postretirement Benefit Costs      
Defined Benefit Plan Disclosure [Line Items]      
COVID-19 related regulatory asset $ 561.6 $ 607.5