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Pension and Postretirement Health and Life Benefits (Schedule of Changes in Projected Benefit Obligations) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Defined Benefit Plan, Actuarial (Gain) Loss From Remeasurement $ 24.6 $ (7.8) $ 50.5
Defined Benefit Plan, Plan Assets, Amount 291.0 486.8  
Pension Plan, Defined Benefit [Member]      
Defined Benefit Plan, Benefit Obligation 308.2 527.3 696.2
Defined Benefit Plan, Actuarial (Gain) Loss From Remeasurement (25.2) (138.0)  
Defined Benefit Plan, Service Cost 2.9 2.7 2.7
Defined Benefit Plan, Interest Cost 27.8 19.1 18.1
Defined Benefit Plan, Benefit Obligation, Increase for Plan Amendment (0.4) 0.0  
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement (171.4) 0.0  
Defined Benefit Plan, Benefit Obligation, Administrative Expenses Paid (3.0) (2.3)  
Defined Benefit Plan, Plan Assets, Amount 290.5 483.3 672.7
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss) 31.8 (137.1)  
Defined Benefit Plan, Plan Assets, Contributions by Employer 0.4 0.4  
Defined Benefit Plan, Plan Assets, Benefits Paid 50.6 50.4  
Defined Benefit Plan, Plan Assets, Payment for Settlement (171.4) 0.0  
Defined Benefit Plan, Plan Assets, Administration Expense (3.0) (2.3)  
Defined Benefit Plan, Funded (Unfunded) Status of Plan (17.7) (44.0)  
Amounts Recognized In Current Liabilities (0.4) (0.4)  
Amounts Recognized In Noncurrent Liabilities (17.3) (43.6)  
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position (17.7) (44.0)  
Recognized In Accumulated Other Comprehensive Income Pre Tax Prior Service Cost Credit (0.1) (0.7)  
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax (0.1) (0.7) (0.9)
Other Postretirement Benefits Plan [Member]      
Defined Benefit Plan, Benefit Obligation 91.3 95.3 131.1
Defined Benefit Plan, Actuarial (Gain) Loss From Remeasurement 1.4 (27.0)  
Defined Benefit Plan, Service Cost 0.0 0.0 0.0
Defined Benefit Plan, Interest Cost 5.0 3.5 3.4
Defined Benefit Plan, Benefit Obligation, Increase for Plan Amendment 0.0 0.0  
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement 0.0 0.0  
Defined Benefit Plan, Benefit Obligation, Administrative Expenses Paid 0.0 0.0  
Defined Benefit Plan, Plan Assets, Amount 0.0 3.5 9.2
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss) 0.1 (0.1)  
Defined Benefit Plan, Plan Assets, Contributions by Employer 6.8 6.7  
Defined Benefit Plan, Plan Assets, Benefits Paid 10.4 12.3  
Defined Benefit Plan, Plan Assets, Payment for Settlement 0.0 0.0  
Defined Benefit Plan, Plan Assets, Administration Expense 0.0 0.0  
Defined Benefit Plan, Funded (Unfunded) Status of Plan (91.3) (91.8)  
Amounts Recognized In Current Liabilities (10.1) (7.3)  
Amounts Recognized In Noncurrent Liabilities (81.2) (84.5)  
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position (91.3) (91.8)  
Recognized In Accumulated Other Comprehensive Income Pre Tax Prior Service Cost Credit (1.8) (1.9)  
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax (1.8) (1.9) $ (2.0)
Plan paid [Member] | Pension Plan, Defined Benefit [Member]      
Defined Benefit Plan, Benefit Obligation, Benefits Paid (50.2) (50.0)  
Plan paid [Member] | Other Postretirement Benefits Plan [Member]      
Defined Benefit Plan, Benefit Obligation, Benefits Paid (10.4) (12.3)  
Company paid [Member] | Pension Plan, Defined Benefit [Member]      
Defined Benefit Plan, Benefit Obligation, Benefits Paid (0.4) (0.4)  
Company paid [Member] | Other Postretirement Benefits Plan [Member]      
Defined Benefit Plan, Benefit Obligation, Benefits Paid $ 0.0 $ 0.0