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Pension and Other Postretirement Benefits (Schedule Of Reconciliation Of The Plans Funded Status And Amounts Reflected) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]      
Noncurrent liabilities $ (231.3) $ (223.1)  
COVID-19 related regulatory asset 2,460.2 2,580.8  
Regulatory Liabilities 1,789.3 2,012.6  
Unrecognized Pension Benefit And Other Postretirement Benefit Costs      
Defined Benefit Plan Disclosure [Line Items]      
Regulatory Liabilities 0.0 0.0  
Unrecognized Pension Benefit And Other Postretirement Benefit Costs      
Defined Benefit Plan Disclosure [Line Items]      
COVID-19 related regulatory asset 561.6 607.5  
Fair Value, Inputs, Level 1, 2 and 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets at beginning of year 1,647.7    
Fair value of plan assets at end of year 1,663.6 1,647.7  
Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Benefit obligation at beginning of year 1,427.4 1,852.4  
Service cost 20.5 27.8 $ 30.2
Interest cost 68.4 40.5 31.4
Plan participants' contributions 0.0 0.0  
Plan amendments 0.0 0.2  
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) 27.4 (318.7)  
Defined Benefit Plan, Benefit Obligation, Benefits Paid 141.9 174.8  
Estimated benefits paid by incurred subsidy 0.0 0.0  
Projected benefit obligation at end of year 1,401.8 1,427.4 1,852.4
Actual return on plan assets 142.8 (386.8)  
Employer contributions 3.1 2.7  
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant 0.0 0.0  
Benefits paid (141.9) (174.8)  
Defined Benefit Plan, Funded (Unfunded) Status of Plan 25.0 (4.6)  
Noncurrent assets 44.1 18.3  
Current liabilities (2.2) (2.6)  
Noncurrent liabilities (16.9) (20.3)  
Net amount recognized at end of year 25.0 (4.6)  
Unrecognized prior service cost 0.3 0.4  
Unrecognized actuarial loss 500.4 564.2  
Defined Benefit Plan Amounts Recognized In Other Comprehensive Income Or Regulatory Asset Or Liability 500.7 564.6  
Pension Plan | Underfunded Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Benefit obligation at beginning of year 1,404.5    
Projected benefit obligation at end of year 1,382.7 1,404.5  
Fair value of plan assets at beginning of year 1,422.8    
Fair value of plan assets at end of year 1,426.8 1,422.8  
Defined Benefit Plan, Funded (Unfunded) Status of Plan 44.1 18.3  
Pension Plan | Underfunded Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Benefit obligation at beginning of year 22.9    
Projected benefit obligation at end of year 19.1 22.9  
Fair value of plan assets at beginning of year 0.0    
Fair value of plan assets at end of year 0.0 0.0  
Defined Benefit Plan, Funded (Unfunded) Status of Plan (19.1) (22.9)  
Pension Plan | Fair Value, Inputs, Level 1, 2 and 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets at beginning of year 1,422.8 1,981.7  
Fair value of plan assets at end of year 1,426.8 1,422.8 1,981.7
Other Postretirement Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Benefit obligation at beginning of year 449.0 556.2  
Service cost 5.1 6.5 6.2
Interest cost 21.8 12.0 9.9
Plan participants' contributions 4.2 4.1  
Plan amendments 3.4 2.1  
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) 29.1 (89.9)  
Defined Benefit Plan, Benefit Obligation, Benefits Paid 44.3 42.3  
Estimated benefits paid by incurred subsidy 0.5 0.3  
Projected benefit obligation at end of year 468.8 449.0 556.2
Actual return on plan assets 28.2 (51.9)  
Employer contributions 23.4 21.3  
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant 4.3 4.1  
Benefits paid (44.3) (42.3)  
Defined Benefit Plan, Funded (Unfunded) Status of Plan (232.3) (224.1)  
Noncurrent assets 0.0 0.0  
Current liabilities (1.0) (1.0)  
Net amount recognized at end of year (232.3) (224.1)  
Unrecognized prior service cost 2.1 (3.4)  
Unrecognized actuarial loss 76.6 64.0  
Defined Benefit Plan Amounts Recognized In Other Comprehensive Income Or Regulatory Asset Or Liability 78.7 60.6  
Other Postretirement Benefits | Fair Value, Inputs, Level 1, 2 and 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets at beginning of year 224.9 293.7  
Fair value of plan assets at end of year $ 236.5 $ 224.9 $ 293.7