Inventory And Vehicle Floorplan Payable (Components Of Vehicle Floorplan Payable) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Floorplan Payable [Line Items]
Vehicle floorplan payable	$ 3,481.1	$ 3,997.7
Trade [Member]
Floorplan Payable [Line Items]
Vehicle floorplan payable	2,073.5	2,388.0
Non-Trade [Member]
Floorplan Payable [Line Items]
Vehicle floorplan payable	$ 1,407.6	$ 1,609.7