Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended					1 Months Ended										12 Months Ended
	Aug. 31, 2014 warehouse	Sep. 01, 2013	Sep. 02, 2012	Aug. 31, 2014 Forward Foreign Exchange Contracts	Sep. 01, 2013 Forward Foreign Exchange Contracts	Jul. 31, 2012 Costco Mexico	Aug. 31, 2014 UNITED STATES states warehouse	Aug. 31, 2014 CANADA warehouse	Aug. 31, 2014 MEXICO warehouse	Aug. 31, 2014 UNITED KINGDOM warehouse	Aug. 31, 2014 JAPAN warehouse	Aug. 31, 2014 KOREA, REPUBLIC OF warehouse	Aug. 31, 2014 TAIWAN, PROVINCE OF CHINA warehouse	Aug. 31, 2014 AUSTRALIA warehouse	Aug. 31, 2014 SPAIN warehouse	Aug. 31, 2014 Building and Building Improvements [Member] Minimum [Member]	Aug. 31, 2014 Building and Building Improvements [Member] Maximum [Member]	Aug. 31, 2014 Furniture and Fixtures [Member] Minimum [Member]	Aug. 31, 2014 Furniture and Fixtures [Member] Maximum [Member]	Aug. 31, 2014 Software [Member] Minimum [Member]	Aug. 31, 2014 Software [Member] Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Minimum Number Of Days Of Employment To Qualify For Retirement Plan	0 years 0 months 90 days
Number Of Warehouses Operated	663						468	88	33	26	20	11	10	6	1
Number Of States In Country							43
Asset Retirement Obligations, Noncurrent	$ 55	$ 50
Maximum Reward Rebate Amount Per Customer Yearly	2.00%
Property, Plant and Equipment, Useful Life																5 years	50 years	3 years	20 years	3 years	7 years
Payments To Acquire Minority Interest	0	0	789
Reduction In Sales	1,051	970	900
Accrued Insurance	815	727
Outstanding Checks Unpresented For Payment	588	493
Credit and Debit Card Receivables, at Carrying Value	1,383	1,254
Purchase of equity interest						50.00%
Inventory, LIFO Reserve, Period Charge (Benefit)	28	(27)	21
Inventory LIFO reserve cumulative impact	109	81
Notional amount of forward foreign - exchange derivative				585	458
Defined Contribution Plan, Cost Recognized	$ 436	$ 409	$ 382