Inventory And Vehicle Floorplan Payable (Components Of Vehicle Floorplan Payable) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Floorplan Payable [Line Items]
Vehicle floorplan payable	$ 3,682.5	$ 3,575.8
Trade [Member]
Floorplan Payable [Line Items]
Vehicle floorplan payable	2,197.2	2,120.6
Non-Trade [Member]
Floorplan Payable [Line Items]
Vehicle floorplan payable	$ 1,485.3	$ 1,455.2