Document and Entity Information	9 Months Ended
	Sep. 30, 2018 shares
Document and Entity Information [Abstract]
Entity Registrant Name	ILLINOIS TOOL WORKS INC
Entity Central Index Key	0000049826
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Entity Emerging Growth Company	false
Entity Small Business	false
Amendment Flag	false
Entity Common Stock, Shares Outstanding	331,801,491