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Postretirement Benefit Cost - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Pension contributions $ 0.5  
Scenario, Forecast | Minimum    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Pension contributions   $ 4.0
Scenario, Forecast | Maximum    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Pension contributions   $ 6.0