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Equity and Comprehensive Income - Additional Information - Dividends (Detail) (USD $)
In Millions, except Per Share data, unless otherwise specified
 3 Months Ended 6 Months Ended
Feb. 15, 2015
Feb. 16, 2014
Feb. 15, 2015
Feb. 16, 2014
Class of Stock [Line Items]        
Dividends declared $ 5.355us-gaap_CommonStockDividendsPerShareDeclared $ 0.31us-gaap_CommonStockDividendsPerShareDeclared $ 5.71us-gaap_CommonStockDividendsPerShareDeclared $ 0.62us-gaap_CommonStockDividendsPerShareDeclared
Payment of dividends $ 2,358us-gaap_PaymentsOfDividends   $ 156us-gaap_PaymentsOfDividends $ 137us-gaap_PaymentsOfDividends
Dividend Declared [Member]        
Class of Stock [Line Items]        
Dividends declared $ 0.355us-gaap_CommonStockDividendsPerShareDeclared
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_DividendDeclaredMember		 $ 0.31us-gaap_CommonStockDividendsPerShareDeclared
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_DividendDeclaredMember		    
Special Dividend [Member]        
Class of Stock [Line Items]        
Dividends declared $ 5us-gaap_CommonStockDividendsPerShareDeclared
/ us-gaap_StatementEquityComponentsAxis
= cost_SpecialDividendMember