Inventory And Vehicle Floorplan Payable (Components Of Vehicle Floorplan Payable) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Floorplan Payable [Line Items]
Vehicle floorplan payable	$ 2,200.8	$ 1,898.8
Trade [Member]
Floorplan Payable [Line Items]
Vehicle floorplan payable	1,559.4	1,362.3
Non-Trade [Member]
Floorplan Payable [Line Items]
Vehicle floorplan payable	$ 641.4	$ 536.5

Amounts borrowed to finance the purchase of specific new vehicle inventories with the corresponding manufacturers' captive finance subsidiaries ("trade lenders") and specific new and, to a lesser extent, used vehicle inventories with non-trade lenders (lenders that are not captive finance subsidiaries of the manufacturer).

No definition available.

Name:	an_VehicleFloorplanPayable
Namespace Prefix:	an_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant