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Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Millions | 12 Months Ended
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Aug. 31, 2025 | Sep. 01, 2024 | Sep. 03, 2023
Summary Of Significant Accounting Policies [Line Items] |  |  |
Deferred membership fees | $ 2,854 | $ 2,501 |
Reduction in sales | $ 3,007 | $ 2,804 | $ 2,576

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- Definition The entity's rewards members receive a cash back reward. These rewards are accounted for as a reduction to sales revenue for this revenue stream. + References No definition available. + Details
Name: | cost_ReductionInSales
Namespace Prefix: | cost_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Summary Of Significant Accounting Policies [Line Items] + References No definition available. + Details
Name: | cost_SummaryOfSignificantAccountingPoliciesLineItems
Namespace Prefix: | cost_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of deferred income and obligation to transfer product and service to customer for which consideration has been received or is receivable, classified as current. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(20)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 + Details
Name: | us-gaap_DeferredRevenueCurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant