Accumulated Other Comprehensive Income (Loss) (Narrative) (Details) - USD ($) $ in Millions	Aug. 31, 2026	Feb. 28, 2026
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Deferred tax	$ 1.2	$ 10.5

The balance of deferred taxes on items remaining in accumulated other comprehensive income loss

No definition available.

Name:	kmx_AccumulatedOtherComprehensiveIncomeLossDeferredTaxes
Namespace Prefix:	kmx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant