| Cover | Mar. 03, 2020 |
| Entity Listings [Line Items] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Mar. 3, 2020 |
| Entity File Number | 1-8002 |
| Entity Registrant Name | THERMO FISHER SCIENTIFIC INC. |
| Entity Central Index Key | 0000097745 |
| Entity Tax Identification Number | 04-2209186 |
| Entity Incorporation, State or Country Code | DE |
| 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 | true |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Stock [Member] | |
| Entity Listings [Line Items] | |
| Common Stock, $1.00 par value | Common Stock, $1.00 par value |
| Trading Symbol | TMO |
| Security Exchange Name | NYSE |
| Floating Rate Notes due 2020 | |
| Entity Listings [Line Items] | |
| Common Stock, $1.00 par value | Floating Rate Notes due 2020 |
| Trading Symbol | TMO /20A |
| Security Exchange Name | NYSE |
| 2.150% Notes due 2022 | |
| Entity Listings [Line Items] | |
| Common Stock, $1.00 par value | 2.150% Notes due 2022 |
| Trading Symbol | TMO 22A |
| Security Exchange Name | NYSE |
| 0.750% Notes due 2024 | |
| Entity Listings [Line Items] | |
| Common Stock, $1.00 par value | 0.750% Notes due 2024 |
| Trading Symbol | TMO 24A |
| Security Exchange Name | NYSE |
| 0.125% Notes due 2025 | |
| Entity Listings [Line Items] | |
| Common Stock, $1.00 par value | 0.125% Notes due 2025 |
| Trading Symbol | TMO 25B |
| Security Exchange Name | NYSE |
| 2.000% Notes due 2025 | |
| Entity Listings [Line Items] | |
| Common Stock, $1.00 par value | 2.000% Notes due 2025 |
| Trading Symbol | TMO 25 |
| Security Exchange Name | NYSE |
| 1.400% Notes due 2026 | |
| Entity Listings [Line Items] | |
| Common Stock, $1.00 par value | 1.400% Notes due 2026 |
| Trading Symbol | TMO 26A |
| Security Exchange Name | NYSE |
| 1.450% Notes due 2027 | |
| Entity Listings [Line Items] | |
| Common Stock, $1.00 par value | 1.450% Notes due 2027 |
| Trading Symbol | TMO 27 |
| Security Exchange Name | NYSE |
| 0.500% Notes due 2028 | |
| Entity Listings [Line Items] | |
| Common Stock, $1.00 par value | 0.500% Notes due 2028 |
| Trading Symbol | TMO 28A |
| Security Exchange Name | NYSE |
| 1.375% Notes due 2028 | |
| Entity Listings [Line Items] | |
| Common Stock, $1.00 par value | 1.375% Notes due 2028 |
| Trading Symbol | TMO 28 |
| Security Exchange Name | NYSE |
| 1.950% Notes due 2029 | |
| Entity Listings [Line Items] | |
| Common Stock, $1.00 par value | 1.950% Notes due 2029 |
| Trading Symbol | TMO 29 |
| Security Exchange Name | NYSE |
| 0.875% Notes due 2031 | |
| Entity Listings [Line Items] | |
| Common Stock, $1.00 par value | 0.875% Notes due 2031 |
| Trading Symbol | TMO 31 |
| Security Exchange Name | NYSE |
| 2.875% Notes due 2037 | |
| Entity Listings [Line Items] | |
| Common Stock, $1.00 par value | 2.875% Notes due 2037 |
| Trading Symbol | TMO 37 |
| Security Exchange Name | NYSE |
| 1.500% Notes due 2039 | |
| Entity Listings [Line Items] | |
| Common Stock, $1.00 par value | 1.500% Notes due 2039 |
| Trading Symbol | TMO 39 |
| Security Exchange Name | NYSE |
| 1.875% Notes due 2049 | |
| Entity Listings [Line Items] | |
| Common Stock, $1.00 par value | 1.875% Notes due 2049 |
| Trading Symbol | TMO 49 |
| Security Exchange Name | NYSE |
