Auto Loan Receivables Auto Loan Receivables (Narrative) (Details) $ in Millions	Nov. 30, 2016 USD ($)
Warehouse Facility Three [Member]
Debt Instrument [Line Items]
Warehouse Facilities Maximum Borrowing Capacity	$ 100

Maximum borrowing capacity under all warehouse facilities without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facilities.

No definition available.

Name:	kmx_WarehouseFacilitiesMaximumBorrowingCapacity
Namespace Prefix:	kmx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant