Inventory And Vehicle Floorplan Payable (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Floorplan Payable [Line Items]
Vehicle floorplan facilities, amount outstanding	$ 2,522.9		$ 3,575.8
Used vehicle floorplan facilities, remaining borrowing capacity	144.7
Used vehicle floorplan facilities, current borrowing capacity	$ 0.4
New Vehicle Floorplan Facilities [Member]
Floorplan Payable [Line Items]
Vehicle floorplan facilities, average LIBOR-based interest rates (percent)	2.30%	3.90%
Vehicle floorplan facilities, maximum borrowing capacity	$ 4,800.0
Vehicle floorplan facilities, amount outstanding	$ 2,200.0
Used Vehicle Floorplan Facilities [Member]
Floorplan Payable [Line Items]
Vehicle floorplan facilities, average LIBOR-based interest rates (percent)	2.60%	3.80%
Vehicle floorplan facilities, maximum borrowing capacity	$ 482.0
Vehicle floorplan facilities, amount outstanding	$ 337.3