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Other Postretirement Employee Benefit Plans (Components Of Net Periodic Benefit Cost) (Details) - Other postretirement benefits - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]      
Service cost $ (0.4) $ (0.4) $ (0.7)
Interest cost (5.3) (5.0)  
Amortization of prior service (cost) credit 2.1 2.5  
Net periodic pension benefit (cost) $ (3.6) $ (2.9) $ (2.9)