Inventory and Vehicle Floorplan Payable (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Floorplan Payable [Line Items]
Vehicle floorplan facilities, amount outstanding	$ 3,029.0	$ 2,540.2
Used vehicle floorplan facilities, current borrowing capacity	50.0
Used vehicle floorplan facilities, remaining borrowing capacity	97.7
Used Vehicle Floorplan Facilities [Member]
Floorplan Payable [Line Items]
Vehicle floorplan facilities, amount outstanding	177.3
Vehicle floorplan facilities, maximum borrowing capacity	275.0
Vehicle floorplan facilities, average LIBOR-based interest rates	1.80%	2.00%
New Vehicle Floorplan Facilities [Member]
Floorplan Payable [Line Items]
Vehicle floorplan facilities, amount outstanding	2,900.0
Vehicle floorplan facilities, maximum borrowing capacity	$ 3,300.0
Vehicle floorplan facilities, average LIBOR-based interest rates	1.90%	2.10%