Document and Entity Information - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Feb. 05, 2022	Jul. 02, 2021
Entity Listings [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Document Transition Report	false
Entity File Number	1-8002
Entity Registrant Name	THERMO FISHER SCIENTIFIC INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	04-2209186
Entity Address, Address Line One	168 Third Avenue
Entity Address, City or Town	Waltham
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02451
City Area Code	781
Local Phone Number	622-1000
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
ICFR Auditor Attestation Flag	true
Entity Public Float			$ 201,672,052
Entity Common Stock, Shares Outstanding		391,191,770
Documents Incorporated by Reference [Text Block]	Sections of Thermo Fisher’s definitive Proxy Statement for the 2022 Annual Meeting of Shareholders are incorporated by reference into Parts II and III of this report.
Entity Central Index Key	0000097745
Amendment Flag	false
Document Fiscal Year Focus	2021
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	FY
Auditor Firm ID	238
Auditor Name	PricewaterhouseCoopers LLP
Auditor Location	Boston, Massachusetts
Common Stock, $1.00 par value
Entity Listings [Line Items]
Title of 12(b) Security	Common Stock, $1.00 par value
Entity Stock Trading Symbol	TMO
Security Exchange Name	NYSE
0.750% Notes due 2024
Entity Listings [Line Items]
Title of 12(b) Security	0.750% Notes due 2024
Entity Stock Trading Symbol	TMO 24A
Security Exchange Name	NYSE
0.125% Notes due 2025
Entity Listings [Line Items]
Title of 12(b) Security	0.125% Notes due 2025
Entity Stock Trading Symbol	TMO 25B
Security Exchange Name	NYSE
2.000% Notes due 2025
Entity Listings [Line Items]
Title of 12(b) Security	2.000% Notes due 2025
Entity Stock Trading Symbol	TMO 25
Security Exchange Name	NYSE
1.400% Notes due 2026
Entity Listings [Line Items]
Title of 12(b) Security	1.400% Notes due 2026
Entity Stock Trading Symbol	TMO 26A
Security Exchange Name	NYSE
1.450% Notes due 2027
Entity Listings [Line Items]
Title of 12(b) Security	1.450% Notes due 2027
Entity Stock Trading Symbol	TMO 27
Security Exchange Name	NYSE
1.750% Notes due 2027
Entity Listings [Line Items]
Title of 12(b) Security	1.750% Notes due 2027
Entity Stock Trading Symbol	TMO 27B
Security Exchange Name	NYSE
0.500% Notes due 2028
Entity Listings [Line Items]
Title of 12(b) Security	0.500% Notes due 2028
Entity Stock Trading Symbol	TMO 28A
Security Exchange Name	NYSE
1.375% Notes due 2028
Entity Listings [Line Items]
Title of 12(b) Security	1.375% Notes due 2028
Entity Stock Trading Symbol	TMO 28
Security Exchange Name	NYSE
1.950% Notes due 2029
Entity Listings [Line Items]
Title of 12(b) Security	1.950% Notes due 2029
Entity Stock Trading Symbol	TMO 29
Security Exchange Name	NYSE
0.875% Notes due 2031
Entity Listings [Line Items]
Title of 12(b) Security	0.875% Notes due 2031
Entity Stock Trading Symbol	TMO 31
Security Exchange Name	NYSE
2.375% Notes due 2032
Entity Listings [Line Items]
Title of 12(b) Security	2.375% Notes due 2032
Entity Stock Trading Symbol	TMO 32
Security Exchange Name	NYSE
2.875% Notes due 2037
Entity Listings [Line Items]
Title of 12(b) Security	2.875% Notes due 2037
Entity Stock Trading Symbol	TMO 37
Security Exchange Name	NYSE
1.500% Notes due 2039
Entity Listings [Line Items]
Title of 12(b) Security	1.500% Notes due 2039
Entity Stock Trading Symbol	TMO 39
Security Exchange Name	NYSE
1.875% Notes due 2049
Entity Listings [Line Items]
Title of 12(b) Security	1.875% Notes due 2049
Entity Stock Trading Symbol	TMO 49
Security Exchange Name	NYSE