Commitments and Contingencies (Details) - USD ($) $ in Millions	3 Months Ended
Jun. 27, 2020	Apr. 03, 2021
Commitments and Contingencies Disclosure [Abstract]
Prepayment For Lease, Leases Not Yet Commenced	$ 50
Lessee, Lease Liability Payments Due, Leases Not Yet Commenced		$ 555

Amount of lessee's undiscounted obligation for lease payments from leases not yet commenced.

No definition available.

Name:	tmo_LesseeLeaseLiabilityPaymentsDueLeasesNotYetCommenced
Namespace Prefix:	tmo_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant