Inventory and Vehicle Floorplan Payable (Components Of Vehicle Floorplan Payable) (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Floorplan Payable [Line Items]
Vehicle floorplan payable	$ 3,796.6	$ 3,709.7
Trade
Floorplan Payable [Line Items]
Vehicle floorplan payable	2,161.4	2,216.2
Non-Trade
Floorplan Payable [Line Items]
Vehicle floorplan payable	$ 1,635.2	$ 1,493.5

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