Inventory And Vehicle Floorplan Payable (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Floorplan Payable [Line Items]
Vehicle floorplan facilities, amount outstanding	$ 3,270.9	$ 3,382.4
Used vehicle floorplan facilities, remaining borrowing capacity	310.4
Used vehicle floorplan facilities, current borrowing capacity	$ 0.3
New Vehicle Floorplan Facilities
Floorplan Payable [Line Items]
Vehicle floorplan facilities, weighted-average interest rate (percent)	7.00%	7.10%
Vehicle floorplan facilities, maximum borrowing capacity	$ 4,700.0
Vehicle floorplan facilities, amount outstanding	$ 2,800.0
Used Vehicle Floorplan Facilities
Floorplan Payable [Line Items]
Vehicle floorplan facilities, weighted-average interest rate (percent)	6.80%	6.90%
Vehicle floorplan facilities, maximum borrowing capacity	$ 810.0
Vehicle floorplan facilities, amount outstanding	$ 499.6