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Pension and Postretirement Health and Life Benefits (Narrative) (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Actuarial (gain) loss from remeasurement, net   $ 25.8 $ (1.4)
Defined Contribution Plan, Cost   2.3 2.4
Scenario, Forecast [Member]      
Expected defined benefit plan contributions for next fiscal year for qualified plans $ 12.8    
Expected defined benefit plan contributions for next fiscal year for non-qualified plans 1.8    
Expected defined benefit plan contributions for next fiscal year for postretirement health and life benefit plans $ 14.6    
Pension Plan, Defined Benefit [Member]      
Defined Benefit Plan, Accumulated Benefit Obligation   817.9 814.6
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)   $ (15.7) 8.1
Approximate Number of Plan Participants   5,000  
Defined Benefit Plan, Plan Assets, Contributions by Employer   $ 1.5 4.1
Actuarial (gain) loss from remeasurement, net   $ 32.8 $ 19.1
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate   3.70% 4.10%
Defined Benefit Plan, Expected Return (Loss) on Plan Assets   $ 40.7 $ 42.0
Other Postretirement Benefit Plan, Defined Benefit [Member]      
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)   $ (7.8) (1.9)
Approximate Number of Plan Participants   3,100  
Defined Benefit Plan, Plan Assets, Contributions by Employer   $ 8.5 6.7
Actuarial (gain) loss from remeasurement, net   $ (24.8) $ (9.2)
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate   3.60% 3.90%
Defined Benefit Plan, Expected Return (Loss) on Plan Assets   $ 0.0 $ 0.3