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Inventory And Vehicle Floorplan Payable (Components Of Inventory) (Details) - USD ($)
$ in Millions
Jun. 30, 2019
Dec. 31, 2018
Inventory [Line Items]    
Inventory $ 3,517.9 $ 3,650.5
New Vehicle [Member]    
Inventory [Line Items]    
Inventory 2,733.8 2,874.8
Used Vehicle [Member]    
Inventory [Line Items]    
Inventory 546.6 553.8
Parts and Service [Member]    
Inventory [Line Items]    
Inventory $ 237.5 $ 221.9