Initial Lease Terms.

No definition available.

Name:	kmx_InitialLeaseTerms
Namespace Prefix:	kmx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Reflects when a long term loan terminates, which may be presented in a variety of ways (year, month and year, day, month and year, quarter).

+ References

No definition available.

+ Details

Name:	kmx_TermLoanExpiratonDate
Namespace Prefix:	kmx_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

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.

+ References

No definition available.

+ Details

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

- Definition

Amount of total borrowing capacity currently available under the warehouse facilities (current borrowing capacity less the amount of borrowings outstanding).

+ References

No definition available.

+ Details

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

- Definition

Warehouse Facility Additional Limit

+ References

No definition available.

+ Details

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

- Definition

Warehouse Facility Additional Term Of Facility

+ References

No definition available.

+ Details

Name:	kmx_WarehouseFacilityAdditionalTermOfFacility
Namespace Prefix:	kmx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Reflects when a warehouse facility terminates, which may be presented in a variety of ways (year, month and year, day, month and year, quarter).

+ References

No definition available.

+ Details

Name:	kmx_WarehouseFacilityExpirationDate
Namespace Prefix:	kmx_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Definition

Latest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(2))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentMaturityDateRangeEnd1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

Name:	us-gaap_LineOfCreditFacilityExpirationDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of increase (decrease) of the credit facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(f))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph f

-Article 4

+ Details

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

- Definition

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

+ References

+ Details

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

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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

- Definition

Amount of debt for which creditor does not have general recourse to the debtor but rather has recourse only to the property used for collateral in the transaction or other specific property.

+ References

No definition available.

+ Details

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

- Definition

Carrying value as of the balance sheet date of debt not otherwise defined (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

+ Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=kmx_TermSecuritizationsDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=kmx_WarehouseFacilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=us-gaap_LongTermDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=kmx_WarehouseFacilityOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=kmx_WarehouseFacilityTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_ScenarioPreviouslyReportedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt (Narrative) (Details) (USD $)	3 Months Ended	9 Months Ended
Debt (Narrative) (Details) (USD $)	Nov. 30, 2014	Nov. 30, 2014	Feb. 28, 2014	Nov. 25, 2014	Jul. 02, 2014
Debt Instrument [Line Items]
Non-recourse notes payable	$ 8,180,000,000us-gaap_NonRecourseDebt	$ 8,180,000,000us-gaap_NonRecourseDebt	$ 7,250,000,000us-gaap_NonRecourseDebt
Other Long-term Debt, Noncurrent	300,000,000us-gaap_OtherLongTermDebtNoncurrent	300,000,000us-gaap_OtherLongTermDebtNoncurrent	0us-gaap_OtherLongTermDebtNoncurrent
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity of revolving credit facility	1,000,000,000	1,000,000,000
Revolving credit facility, expiration date		Aug. 01, 2016
Revolving Credit Facility, Remaining Borrowing Capacity	997,000,000	997,000,000
Revolving Credit Facility, Increase (Decrease)	300,000,000
Warehouse Facilities [Member]
Debt Instrument [Line Items]
Non-recourse notes payable	959,000,000	959,000,000
Warehouse facilities maximum borrowing capacity	2,300,000,000	2,300,000,000
Remaining borrowing capacity	1,340,000,000	1,340,000,000
Term Securitizations Debt [Member]
Debt Instrument [Line Items]
Debt maturity, end		May 01, 2021
Non-recourse notes payable	7,220,000,000	7,220,000,000
Long-term Debt [Member]
Debt Instrument [Line Items]
Term Loan expiraton date		Nov. 01, 2017
Warehouse Facility One [Member] \| Warehouse Facilities [Member]
Debt Instrument [Line Items]
Warehouse facilities maximum borrowing capacity	800,000,000	800,000,000
Warehouse facility expiration date	Jul. 01, 2015
Warehouse facility additional term of facility, days		364 days
Warehouse Facility Two [Member] \| Warehouse Facilities [Member]
Debt Instrument [Line Items]
Warehouse Facility Additional Limit				200,000,000	300,000,000
Warehouse facilities maximum borrowing capacity	1,500,000,000	1,500,000,000
Warehouse facility expiration date		Feb. 01, 2015
Previously Reported [Member] \| Warehouse Facility One [Member] \| Warehouse Facilities [Member]
Debt Instrument [Line Items]
Warehouse facilities maximum borrowing capacity	$ 800,000,000	$ 800,000,000
Minimum [Member] \| Finance And Capital Lease Obligation [Member]
Debt Instrument [Line Items]
Initial lease terms, in years		15 years
Maximum [Member] \| Finance And Capital Lease Obligation [Member]
Debt Instrument [Line Items]
Initial lease terms, in years		20 years