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Employee Benefit Plans (Narrative) (Details)
$ in Millions
6 Months Ended
Jun. 30, 2018
USD ($)
Defined Benefit Pension Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Employer contributions $ 17.2
Estimated minimum contributions 32.9
Postretirement Health Coverage [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Employer contributions 0.7
Estimated minimum contributions $ 1.6