DOCUMENT AND ENTITY INFORMATION	3 Months Ended
	Mar. 31, 2017 shares
Document and Entity Information [Abstract]
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	Mar. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding	58,405,698