Item as percent of total ending managed receivables

No definition available.

Name:	kmx_ItemAsPercentOfTotalEndingManagedReceivables
Namespace Prefix:	kmx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

+ References

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-Publisher FASB
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+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of increase in allowance for credit loss on financing receivable from recovery.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
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+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of writeoff of financing receivable, charged against allowance for credit loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.

+ References

+ Details

Name:	us-gaap_ProvisionForLoanLeaseAndOtherLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_ValuationAllowancesAndReservesTypeAxis=us-gaap_AllowanceForLoanAndLeaseLossesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
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- Details

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Auto Loan Receivables (Allowance For Loan Losses) (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Nov. 30, 2020	May 31, 2020	Nov. 30, 2019	Nov. 30, 2020	Nov. 30, 2019	Nov. 30, 2020	Aug. 31, 2020	Mar. 01, 2020	Feb. 29, 2020	Nov. 30, 2019	Aug. 31, 2019	Feb. 28, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance as of beginning of period	$ 432,500	$ 157,796	$ 150,400	$ 157,796	$ 138,200
Financing Receivable, Allowance for Credit Loss	432,500	157,796	153,600	157,796	153,600	$ 431,592	$ 432,500	$ 359,800	$ 157,796	$ 153,600	$ 150,400	$ 138,200
Financing Receivable, Allowance for Credit Loss, Writeoff	(49,900)		(81,200)	(174,500)	(223,400)
Financing Receivable, Allowance for Credit Loss, Recovery	40,800		35,400	90,200	106,100
Provision for loan losses	8,200	$ 122,000	49,000	156,100	132,700
Balance as of end of period	$ 431,592		$ 153,600	$ 431,592	$ 153,600
Allowance For Loan Losses, percent
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Item as percent of total ending managed receivables						3.17%	3.23%	2.64%	1.16%	1.15%	1.15%	1.10%
Accounting Standards Update 2016-13 [Member] \| Financing Receivable [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss								$ 202,000