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Pension and Other Postretirement Benefits (Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]      
COVID-19 related regulatory asset $ 2,580.8 $ 2,492.2  
Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Accumulated Benefit Obligation 1,416.8 1,834.4  
Funded status of plan 4.6 (129.3)  
Employer contributions 2.7 4.0  
Settlement loss 12.4 11.4 $ 10.5
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement 5.7 $ 4.0  
Expected contribution $ 2.6    
Expected return on plan assets 4.80% 5.20% 5.70%
Other Postretirement Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Funded status of plan $ 224.1 $ 262.5  
Employer contributions 21.3 19.8  
Settlement loss 0.0 $ 0.0 $ 1.5
Expected contribution $ 23.7    
Expected return on plan assets 5.72% 5.50% 5.67%
Unrecognized Pension Benefit And Other Postretirement Benefit Costs      
Defined Benefit Plan Disclosure [Line Items]      
COVID-19 related regulatory asset $ 607.5 $ 512.1