v2.4.0.6
Summary of Significant Policies - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 1 Months Ended 3 Months Ended 4 Months Ended 12 Months Ended
Jul. 31, 2012
May 08, 2011
Feb. 13, 2011
Sep. 02, 2012
Aug. 28, 2011
Sep. 02, 2012
Aug. 28, 2011
Aug. 29, 2010
Summary Of Significant Accounting Policies [Line Items]                
Number of warehouses operated           608    
Increase to total assets and liabilities due to consolidation             3.00%  
Initial consolidation of noncontrolling interest in the Costco Mexico joint ventures         $ 357   $ 357  
Purchase of equity interest 50.00%              
Purchase of noncontrolling interest in Costco Mexico 789         789 0 0
Cash dividend declared 366              
Credit and debit card receivables       1,161 982 1,161 982  
Charge to merchandise costs   49 6 12 32 21 87  
Inventory LIFO reserve       108 87 108 87  
Excess of outstanding checks over cash on deposit       565 108 565 108  
Estimated accruals for insurance liabilities       688 595 688 595  
Gain (loss) on foreign currency transaction           41 8 13
Reward rate           2.00%    
Reduction in sales           900 790 688
Foreign Exchange Forward
                
Summary Of Significant Accounting Policies [Line Items]                
Notional amount of forward foreign - exchange derivative       284 247 284 247  
Building and Building Improvements | Minimum
                
Summary Of Significant Accounting Policies [Line Items]                
Property and equipment, useful life           5 years    
Building and Building Improvements | Maximum
                
Summary Of Significant Accounting Policies [Line Items]                
Property and equipment, useful life           50 years    
Furniture and Fixtures | Minimum
                
Summary Of Significant Accounting Policies [Line Items]                
Property and equipment, useful life           3 years    
Furniture and Fixtures | Maximum
                
Summary Of Significant Accounting Policies [Line Items]                
Property and equipment, useful life           20 years    
Software | Minimum
                
Summary Of Significant Accounting Policies [Line Items]                
Property and equipment, useful life           3 years    
Software | Maximum
                
Summary Of Significant Accounting Policies [Line Items]                
Property and equipment, useful life           7 years    
Subsidiaries
                
Summary Of Significant Accounting Policies [Line Items]                
Percentage of dividend payable 50.00%              
Costco Mexico
                
Summary Of Significant Accounting Policies [Line Items]                
Percentage of dividend payable 50.00%              
Equity in earnings of Costco Mexico               $ 41
UNITED STATES
                
Summary Of Significant Accounting Policies [Line Items]                
Number of warehouses operated           439    
US and Puerto Rico
                
Summary Of Significant Accounting Policies [Line Items]                
Number of regions in country           40    
CANADA
                
Summary Of Significant Accounting Policies [Line Items]                
Number of warehouses operated           82    
Number of regions in country           9    
MEXICO
                
Summary Of Significant Accounting Policies [Line Items]                
Number of warehouses operated           32    
UNITED KINGDOM
                
Summary Of Significant Accounting Policies [Line Items]                
Number of warehouses operated           22    
JAPAN
                
Summary Of Significant Accounting Policies [Line Items]                
Number of warehouses operated           13    
TAIWAN, PROVINCE OF CHINA
                
Summary Of Significant Accounting Policies [Line Items]                
Number of warehouses operated           9    
KOREA, REPUBLIC OF
                
Summary Of Significant Accounting Policies [Line Items]                
Number of warehouses operated           8    
AUSTRALIA
                
Summary Of Significant Accounting Policies [Line Items]                
Number of warehouses operated           3