Inventory And Vehicle Floorplan Payable (Narrative) (Details) (USD $) In Millions, unless otherwise specified			9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Used Vehicle Floorplan Facilities [Member]	Sep. 30, 2012 Used Vehicle Floorplan Facilities [Member]	Sep. 30, 2013 New Vehicle Floorplan Facilities [Member]	Sep. 30, 2012 New Vehicle Floorplan Facilities [Member]
Floorplan Payable [Line Items]
Vehicle floorplan facilities, average LIBOR-based interest rates			1.80%	2.10%	2.00%	2.10%
Vehicle floorplan facilities, maximum borrowing capacity			$ 275.0		$ 3,000.0
Vehicle floorplan facilities, amount outstanding	2,600.9	2,540.2	174.1		2,400.0
Used vehicle floorplan facilities, remaining borrowing capacity	100.9
Used vehicle floorplan facilities, current borrowing capacity	$ 47.6