Cash payment per cash settled restricted stock unit

No definition available.

Name:	kmx_CashPaymentPerCashSettledRestrictedStockUnit
Namespace Prefix:	kmx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Market Stock Units Converted To Common Stock Conversion Ratio Number Of Final Trading Days In Vesting Period

+ References

No definition available.

+ Details

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

- Definition

Market stock units converted to common stock for each unit granted

+ References

No definition available.

+ Details

Name:	kmx_MarketStockUnitsConvertedToCommonStockForEachUnitGranted
Namespace Prefix:	kmx_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Payment related to restricted stock units vested during the period

+ References

No definition available.

+ Details

Name:	kmx_PaymentRelatedToRestrictedStockUnitsVestedDuringPeriod
Namespace Prefix:	kmx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period

+ References

No definition available.

+ Details

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

- Definition

Stock repurchase program, authorization expiration

+ References

No definition available.

+ Details

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

- Definition

Represents the compensation cost capitalized during the period arising from equity-based compensation arrangements (for example, shares of stock, units, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(1)(ii)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

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

- Definition

Aggregate proceeds received by the entity during the annual period from exercises of stock or unit options and conversion of similar instruments granted under equity-based payment arrangements.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (j)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

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

- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Disclosure of the aggregate tax benefit realized from the exercise of stock options and the conversion of similar instruments during the annual period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (j)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

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

- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)(iii)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)(iii)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)(i)-(ii)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Details

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

- Definition

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (d)(2)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

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

- Definition

Net number of share options (or share units) granted during the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(iv)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Gross number of share options (or share units) granted during the period.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (d)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of stock repurchase plan authorized.

+ References

No definition available.

+ Details

Name:	us-gaap_StockRepurchaseProgramAuthorizedAmount1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount remaining of a stock repurchase plan authorized.

+ References

No definition available.

+ Details

Name:	us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Total cost of shares repurchased divided by the total number of shares repurchased.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 30

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655

+ Details

Name:	us-gaap_TreasuryStockAcquiredAverageCostPerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares that have been repurchased during the period and are being held in treasury.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29, 30

-Article 5

+ Details

Name:	us-gaap_TreasuryStockSharesAcquired
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_AwardTypeAxis=kmx_CashSettledRestrictedStockUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=kmx_ShareRepurchaseProgramMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=kmx_StockSettledRestrictedStockUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_StockCompensationPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_StockOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShareRepurchaseProgramAxis=kmx_FY2013ShareRepurchaseAuthorizationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShareRepurchaseProgramAxis=kmx_March2014AuthorizationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShareRepurchaseProgramAxis=kmx_October2014AuthorizationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Stock And Stock-Based Incentive Plans (Narrative) (Details) (USD $)	9 Months Ended	3 Months Ended		9 Months Ended
	Nov. 30, 2014	Nov. 30, 2014	Nov. 30, 2013	Nov. 30, 2013	Feb. 28, 2014
FY 2013 Share Repurchase Authorizations Member
Stock and Stock-Based Incentive Plans
Share repurchase, authorized amount	$ 800,000,000	$ 800,000,000
March 2014 Authorization [Member]
Stock and Stock-Based Incentive Plans
Share repurchase, authorized amount	1,000,000,000	1,000,000,000
Share repurchase, authorization expiration	Dec. 31, 2015
October 2014 Authorization [Member]
Stock and Stock-Based Incentive Plans
Share repurchase, authorized amount	2,000,000,000	2,000,000,000
Share repurchase, authorization expiration	Dec. 31, 2016
Share Repurchase Program [Member]
Stock and Stock-Based Incentive Plans
Shares repurchased during the period	14,101,539	6,234,799	313,042	4,305,293
Share repurchase, average purchase price per share	$ 49.80	$ 52.48	$ 47.39	$ 43.69
Share repurchase, amount remaining for repurchase	2,580,000,000	2,580,000,000
Share Repurchase Program [Member] \| FY 2013 Share Repurchase Authorizations Member
Stock and Stock-Based Incentive Plans
Share repurchase, authorized amount	800,000,000	800,000,000
Stock Compensation Plan [Member]
Stock and Stock-Based Incentive Plans
Incentive stock option grants in period	0
Capitalized share-based compensation	0			0
Stock Option [Member]
Stock and Stock-Based Incentive Plans
Options granted, Number of Shares	2,050,919			1,605,149
Cash received as a result of stock option exercises	54,300,000			26,000,000
Total intrinsic value of options exercised	99,900,000			34,700,000
Related tax benefits	40,200,000			13,900,000
Options granted, weighted average grant date fair value	$ 13.25			$ 15.59
Unrecognized compensation costs related to nonvested options/MSU/RSA	38,200,000	38,200,000
Weighted average period, years	2 years 7 months 6 days
Stock Option [Member] \| Minimum [Member]
Stock and Stock-Based Incentive Plans
Vesting period, in years	1 year
Stock Option [Member] \| Maximum [Member]
Stock and Stock-Based Incentive Plans
Vesting period, in years	4 years
Years until expiration	10 years
Cash-Settled Restricted Stock Units [Member]
Stock and Stock-Based Incentive Plans
Vesting period, in years	3 years
Restricted stock awards granted, number of shares	587,990			541,819
Restricted stock granted, weighted average grant date fair value	$ 44.96			$ 42.68
Related tax benefits	8,700,000			9,300,000
Payment related to restricted stock units vested during the period	21,600,000			23,300,000
Awards outstanding	1,558,000	1,558,000			1,531,000
Cash-Settled Restricted Stock Units [Member] \| Minimum [Member]
Stock and Stock-Based Incentive Plans
Cash payment per RSU, percentage	75.00%
Cash-Settled Restricted Stock Units [Member] \| Maximum [Member]
Stock and Stock-Based Incentive Plans
Cash payment per RSU, percentage	200.00%
Stock-Settled Restricted Stock Units [Member]
Stock and Stock-Based Incentive Plans
Vesting period, in years	3 years
Conversion ratio, number of final trading days in vesting period	40 days
Restricted stock awards granted, number of shares	249,291			237,660
Restricted stock granted, weighted average grant date fair value	$ 55.42			$ 52.02
Related tax benefits	7,500,000			6,700,000
Unrecognized compensation costs related to nonvested options/MSU/RSA	16,200,000	16,200,000
Weighted average period, years	1 year 4 months 24 days
Awards outstanding	800,000	800,000			852,000
Stock-Settled Restricted Stock Units [Member] \| Minimum [Member]
Stock and Stock-Based Incentive Plans
MSUs converted to common stock	0
Stock-Settled Restricted Stock Units [Member] \| Maximum [Member]
Stock and Stock-Based Incentive Plans
MSUs converted to common stock	2
Restricted Stock Awards [Member]
Stock and Stock-Based Incentive Plans
Vesting period, in years	1 year 0 months 0 days
Restricted stock awards granted, number of shares	22,860
Restricted stock granted, weighted average grant date fair value	$ 51.18
Unrecognized compensation costs related to nonvested options/MSU/RSA	$ 100,000	$ 100,000
Weighted average period, years	0 years 7 months 6 days
Awards outstanding			0	0