DOCUMENT AND ENTITY INFORMATION - Jun. 30, 2015 - USD ($)	Total
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-Q
Document Period End Date	Jun. 30, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q2
Amendment Flag	false
Entity Common Stock, Shares Outstanding	65,975,137
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float	$ 14,934,345,621