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Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Feb. 15, 2015
warehouse
Feb. 16, 2014
Feb. 15, 2015
warehouse
Feb. 16, 2014
Aug. 31, 2014
Summary Of Significant Accounting Policies [Line Items]          
Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments $ (12)us-gaap_GainLossOnForeignCurrencyDerivativeInstrumentsNotDesignatedAsHedgingInstruments   $ 11us-gaap_GainLossOnForeignCurrencyDerivativeInstrumentsNotDesignatedAsHedgingInstruments    
Foreign Currency Transaction Gain (Loss), before Tax 14us-gaap_ForeignCurrencyTransactionGainLossBeforeTax 10us-gaap_ForeignCurrencyTransactionGainLossBeforeTax 12us-gaap_ForeignCurrencyTransactionGainLossBeforeTax 19us-gaap_ForeignCurrencyTransactionGainLossBeforeTax  
Number Of Warehouses Operated 671cost_NumberOfWarehousesOperated   671cost_NumberOfWarehousesOperated    
Inventory LIFO reserve cumulative impact 103us-gaap_InventoryLIFOReserve   103us-gaap_InventoryLIFOReserve   109us-gaap_InventoryLIFOReserve
Forward Foreign Exchange Contracts          
Summary Of Significant Accounting Policies [Line Items]          
Notional amount of forward foreign - exchange derivative 1,108invest_DerivativeNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= us-gaap_ForeignExchangeForwardMember
  1,108invest_DerivativeNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= us-gaap_ForeignExchangeForwardMember
  585invest_DerivativeNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= us-gaap_ForeignExchangeForwardMember
Forward Foreign Exchange Contracts          
Summary Of Significant Accounting Policies [Line Items]          
Notional amount of forward foreign - exchange derivative $ 350invest_DerivativeNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= cost_ForeignExchangeForwardCanadianDollarMember
  $ 350invest_DerivativeNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= cost_ForeignExchangeForwardCanadianDollarMember
   
UNITED STATES          
Summary Of Significant Accounting Policies [Line Items]          
Number Of Warehouses Operated 474cost_NumberOfWarehousesOperated
/ us-gaap_StatementGeographicalAxis
= country_US
  474cost_NumberOfWarehousesOperated
/ us-gaap_StatementGeographicalAxis
= country_US
   
Number of states in country 43cost_NumberOfStatesInCountry
/ us-gaap_StatementGeographicalAxis
= country_US
  43cost_NumberOfStatesInCountry
/ us-gaap_StatementGeographicalAxis
= country_US
   
CANADA          
Summary Of Significant Accounting Policies [Line Items]          
Number Of Warehouses Operated 88cost_NumberOfWarehousesOperated
/ us-gaap_StatementGeographicalAxis
= country_CA
  88cost_NumberOfWarehousesOperated
/ us-gaap_StatementGeographicalAxis
= country_CA
   
MEXICO          
Summary Of Significant Accounting Policies [Line Items]          
Number Of Warehouses Operated 34cost_NumberOfWarehousesOperated
/ us-gaap_StatementGeographicalAxis
= country_MX
  34cost_NumberOfWarehousesOperated
/ us-gaap_StatementGeographicalAxis
= country_MX
   
UNITED KINGDOM          
Summary Of Significant Accounting Policies [Line Items]          
Number Of Warehouses Operated 26cost_NumberOfWarehousesOperated
/ us-gaap_StatementGeographicalAxis
= country_GB
  26cost_NumberOfWarehousesOperated
/ us-gaap_StatementGeographicalAxis
= country_GB
   
JAPAN          
Summary Of Significant Accounting Policies [Line Items]          
Number Of Warehouses Operated 20cost_NumberOfWarehousesOperated
/ us-gaap_StatementGeographicalAxis
= country_JP
  20cost_NumberOfWarehousesOperated
/ us-gaap_StatementGeographicalAxis
= country_JP
   
TAIWAN, PROVINCE OF CHINA          
Summary Of Significant Accounting Policies [Line Items]          
Number Of Warehouses Operated 10cost_NumberOfWarehousesOperated
/ us-gaap_StatementGeographicalAxis
= country_TW
  10cost_NumberOfWarehousesOperated
/ us-gaap_StatementGeographicalAxis
= country_TW
   
KOREA, REPUBLIC OF          
Summary Of Significant Accounting Policies [Line Items]          
Number Of Warehouses Operated 11cost_NumberOfWarehousesOperated
/ us-gaap_StatementGeographicalAxis
= country_KR
  11cost_NumberOfWarehousesOperated
/ us-gaap_StatementGeographicalAxis
= country_KR
   
AUSTRALIA          
Summary Of Significant Accounting Policies [Line Items]          
Number Of Warehouses Operated 7cost_NumberOfWarehousesOperated
/ us-gaap_StatementGeographicalAxis
= country_AU
  7cost_NumberOfWarehousesOperated
/ us-gaap_StatementGeographicalAxis
= country_AU
   
SPAIN          
Summary Of Significant Accounting Policies [Line Items]          
Number Of Warehouses Operated 1cost_NumberOfWarehousesOperated
/ us-gaap_StatementGeographicalAxis
= country_ES
  1cost_NumberOfWarehousesOperated
/ us-gaap_StatementGeographicalAxis
= country_ES