Inventory And Vehicle Floorplan Payable (Components Of Vehicle Floorplan Payable) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Floorplan Payable [Line Items]
Vehicle floorplan payable	$ 3,630.5	$ 3,849.2
Trade [Member]
Floorplan Payable [Line Items]
Vehicle floorplan payable	2,069.3	2,308.8
Non-Trade [Member]
Floorplan Payable [Line Items]
Vehicle floorplan payable	$ 1,561.2	$ 1,540.4