Document and Entity Information	3 Months Ended
	Mar. 30, 2019 shares
Document and Entity Information [Abstract]
Entity Registrant Name	THERMO FISHER SCIENTIFIC INC.
Entity Central Index Key	0000097745
Document Type	10-Q
Document Period End Date	Mar. 30, 2019
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding	399,981,140
Entity Stock Trading Symbol	TMO