MandatoryProportionalAdjustmentSharesAvailableToGrant

No definition available.

Name:	cost_MandatoryProportionalAdjustmentSharesAvailableToGrant
Namespace Prefix:	cost_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Mandatory adjustment to restricted stock units outstanding as of the effect date of a special cash dividend.

+ References

No definition available.

+ Details

Name:	cost_MandatoryProportionalAdjustmentedtoRestrictedStockUnits
Namespace Prefix:	cost_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of performance-based compensation awards granted to executive officers upon achievement of the specified performance targets as approved by the Company's Board of Directors.

+ References

No definition available.

+ Details

Name:	cost_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingPerformanceBasedToBeGranted
Namespace Prefix:	cost_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of time-based compensation restricted stock units outstanding at the end of the period.

+ References

No definition available.

+ Details

Name:	cost_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingTimeBased
Namespace Prefix:	cost_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the outstanding shares adjustment ratio of the NASDAQ closing price the day before to the NASDAQ opening price, the ex-dividend date.

+ References

No definition available.

+ Details

Name:	cost_SpecialCashDividendSharesAdjustmentRatio
Namespace Prefix:	cost_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=120381028&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 cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
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://fasb.org/us-gaap/role/ref/legacyRef
-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=120381028&loc=d3e5070-113901

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Number of additional shares authorized for issuance under share-based payment arrangement.

+ References

No definition available.

+ Details

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

- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

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

- Definition

Price of a single share of a number of saleable stocks of a company.

+ References

No definition available.

+ Details

Name:	us-gaap_SharePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_PlanNameAxis=cost_A2019IncentivePlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
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Stock-Based Compensation Plans - Additional Information (Detail) $ / shares in Units, $ in Millions	6 Months Ended
	Feb. 14, 2021 USD ($) shares	Dec. 11, 2020 closingSharePricePerOpeningSharePrice	Dec. 01, 2020 $ / shares	Nov. 30, 2020 $ / shares	Aug. 30, 2020 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares	4,416,000				5,174,000
MandatoryProportionalAdjustmentedtoRestrictedStockUnits	(94,000)
Share Price \| $ / shares			$ 384.50	$ 391.77
Additional number of shares authorized	222,000
SpecialCashDividendSharesAdjustmentRatio \| closingSharePricePerOpeningSharePrice		1.019
2019 Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional number of shares authorized	17,500,000
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional number of shares authorized	10,000,000
Number of shares available to be granted	11,946,000
Time-based RSUs awards outstanding	4,285,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares	29,000
Unrecognized compensation cost \| $	$ 951
Weighted-average recognition period	1 year 8 months 12 days
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding performance-based RSUs awards granted, subject to achievement of performance targets	102,000
Maximum [Member] \| 2019 Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available to be granted	27,800,000
Maximum [Member] \| Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available to be granted	15,885,000