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Subsequent Events (Details) - Forecast - Subsequent Event
$ in Millions
1 Months Ended
Oct. 31, 2020
USD ($)
Minimum  
Subsequent Event [Line Items]  
Unamortized net unrecognized postretirement benefit costs $ 45.0
Maximum  
Subsequent Event [Line Items]  
Unamortized net unrecognized postretirement benefit costs $ 55.0