v2.4.0.6
DOCUMENT AND ENTITY INFORMATION (USD $)
12 Months Ended
Dec. 31, 2011
Jun. 30, 2011
Document Information [Line Items]    
Entity Registrant Name GRAINGER W W INC  
Entity Central Index Key 0000277135  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Document Type 10-K  
Document Period End Date Dec. 31, 2011  
Document Fiscal Year Focus 2011  
Document Fiscal Period Focus Q4  
Amendment Flag false  
Entity Common Stock, Shares Outstanding 69,962,852  
Entity Well-known Seasoned Issuer Yes  
Entity Voluntary Filers No  
Entity Current Reporting Status Yes  
Entity Public Float   $ 10,123,345,795