Debt, Interest Rate Swap Arrangements (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Notional Amount Of Derivatives	$ 6,360.0	$ 6,700.0
Senior Notes [Member] \| 4.50% Senior Notes Due 2021 [Member] \| Interest Rate Swaps [Member]
Debt Instrument [Line Items]
Notional Amount Of Derivatives	$ 1,000.0
Interest Rate Swap, Pay Rate Spread above One-month LIBOR	3.442%
Interest Rate Swap, Pay Rate at Period End	4.6792%
Interest Rate Swap, Fixed Receive Rate	4.50%
Senior Notes [Member] \| 3.60% Senior Notes Due 2021 [Member] \| Interest Rate Swaps [Member]
Debt Instrument [Line Items]
Notional Amount Of Derivatives	$ 1,100.0
Interest Rate Swap, Pay Rate Spread above One-month LIBOR	2.515%
Interest Rate Swap, Pay Rate at Period End	3.7494%
Interest Rate Swap, Fixed Receive Rate	3.60%
Senior Notes [Member] \| 3.00% Senior Notes Due 2023 [Member] \| Interest Rate Swaps [Member]
Debt Instrument [Line Items]
Notional Amount Of Derivatives	$ 1,000.0
Interest Rate Swap, Pay Rate Spread above One-month LIBOR	1.764%
Interest Rate Swap, Pay Rate at Period End	2.9984%
Interest Rate Swap, Fixed Receive Rate	3.00%

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

+ Details

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage points added to the reference rate to compute the variable rate on the interest rate derivative.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeBasisSpreadOnVariableRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Fixed interest rate related to the interest rate derivative.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeFixedInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Variable interest rate in effect as of the balance sheet date related to the interest rate derivative.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeVariableInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=tmo_SeniorNotes450Due2021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=tmo_SeniorNotes360Due2021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=tmo_SeniorNotes3.00Due2023Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: