FLOOR PLAN NOTES PAYABLE—NON-TRADE - Consist of (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Debt Disclosure [Abstract]
Floor plan notes payable—new non-trade	$ 1,359.8	$ 1,328.1
Floor plan notes payable—used non-trade	100.7	307.1
Floor plan notes payable offset account	(115.7)	(44.7)
Total floor plan notes payable—non-trade, net	$ 1,344.8	$ 1,590.6

Amounts borrowed to finance the purchase of 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:	abg_FloorPlanNotesPayableNonTrade
Namespace Prefix:	abg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant