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Inventory And Vehicle Floorplan Payable (Components Of Inventory) (Details) - USD ($)
$ in Millions
Mar. 31, 2016
Dec. 31, 2015
Inventory [Line Items]    
Inventory $ 3,927.8 $ 3,612.0
New Vehicle [Member]    
Inventory [Line Items]    
Inventory 3,186.1 2,888.1
Used Vehicle [Member]    
Inventory [Line Items]    
Inventory 551.3 539.7
Parts and Service [Member]    
Inventory [Line Items]    
Inventory $ 190.4 $ 184.2