| Document and Entity Information | Sep. 24, 2019 |
| Document And Entity Information [Line Items] | |
| Amendment Flag | false |
| Entity Central Index Key | 0000097745 |
| Document Type | 8-K |
| Document Period End Date | Sep. 24, 2019 |
| Entity Registrant Name | THERMO FISHER SCIENTIFIC INC. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 1-8002 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Stock [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Common Stock, $1.00 par value |
| Trading Symbol | TMO |
| Security Exchange Name | NYSE |
| Senior Notes Floating Rate Due 2020 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Floating Rate Notes due 2020 |
| Trading Symbol | TMO /20A |
| Security Exchange Name | NYSE |
| Senior Notes 1.50due 2020 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 1.500% Notes due 2020 |
| Trading Symbol | TMO 20A |
| Security Exchange Name | NYSE |
| Senior Notes 2.15 Due 2022 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 2.150% Notes due 2022 |
| Trading Symbol | TMO 22A |
| Security Exchange Name | NYSE |
| Senior Notes 0.75 Due 2024 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 0.750% Notes due 2024 |
| Trading Symbol | TMO 24A |
| Security Exchange Name | NYSE |
| Senior Notes 200 Due 2025 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 2.000% Notes due 2025 |
| Trading Symbol | TMO 25 |
| Security Exchange Name | NYSE |
| Senior Notes 1.40 Due 2026 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 1.400% Notes due 2026 |
| Trading Symbol | TMO 26A |
| Security Exchange Name | NYSE |
| A 1.45 Senior Notes Due 2027 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 1.450% Notes due 2027 |
| Trading Symbol | TMO 27 |
| Security Exchange Name | NYSE |
| Senior Notes 1.375 Due 2028 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 1.375% Notes due 2028 |
| Trading Symbol | TMO 28 |
| Security Exchange Name | NYSE |
| Senior Notes 1.95 Due 2029 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 1.950% Notes due 2029 |
| Trading Symbol | TMO 29 |
| Security Exchange Name | NYSE |
| Senior Notes 2.875 Due 2037 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 2.875% Notes due 2037 |
| Trading Symbol | TMO 37 |
| Security Exchange Name | NYSE |
