CONDENSED CONSOLIDATED STATEMENTS OF REDEEMABLE NONCONTROLLING INTEREST AND EQUITY (Unaudited) - USD ($) $ in Millions	Total	Total Thermo Fisher Scientific Inc. Shareholders’ Equity	Common Stock	Capital in Excess of Par Value	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income/(Loss)	Noncontrolling Interests
Beginning Balance at Dec. 31, 2023	$ 118
Redeemable Noncontrolling Interest [Roll Forward]
Net income/(loss)	10
Other comprehensive income/(loss)	(6)
Contributions from (distributions to) noncontrolling interests	(7)
Ending Balance at Jun. 29, 2024	115
Balance (in shares) at Dec. 31, 2023			442,000,000
Beginning Balance at Dec. 31, 2023	46,724	$ 46,735	$ 442	$ 17,286	$ 47,364	$ (15,133)	$ (3,224)	$ (11)
Treasury stock beginning balance (in shares) at Dec. 31, 2023						56,000,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under stock plans (in shares)			1,000,000
Issuance of shares under stock plans	184	184	$ 1	209		$ (26)
Stock-based compensation	154	154		154
Purchases of company common stock (in shares)						6,000,000
Purchases of company common stock	(3,000)	(3,000)				$ (3,000)
Dividends declared	(298)	(298)			(298)
Net income/(loss)	2,874	2,875			2,875			(1)
Other comprehensive income/(loss)	811	811					811
Contributions from (distributions to) noncontrolling interests	(1)							(1)
Excise tax from stock repurchases	(28)	(28)				$ (28)
Balance (in shares) at Jun. 29, 2024			443,000,000
Treasury stock ending balance (in shares) at Jun. 29, 2024						61,000,000
Ending Balance at Jun. 29, 2024	47,419	47,432	$ 443	17,649	49,940	$ (18,187)	(2,413)	(12)
Beginning Balance at Mar. 30, 2024	119
Redeemable Noncontrolling Interest [Roll Forward]
Net income/(loss)	6
Other comprehensive income/(loss)	(3)
Contributions from (distributions to) noncontrolling interests								(7)
Ending Balance at Jun. 29, 2024	115
Balance (in shares) at Mar. 30, 2024			443,000,000
Beginning Balance at Mar. 30, 2024	45,504	45,516	$ 443	17,482	48,542	$ (18,186)	(2,764)	(12)
Treasury stock beginning balance (in shares) at Mar. 30, 2024						61,000,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under stock plans (in shares)			0
Issuance of shares under stock plans	81	81		83		$ (2)
Stock-based compensation	84	84		84
Dividends declared	(149)	(149)			(149)
Net income/(loss)	1,548	1,548			1,548
Other comprehensive income/(loss)	351	351					351
Excise tax from stock repurchases	1	1				$ 1
Balance (in shares) at Jun. 29, 2024			443,000,000
Treasury stock ending balance (in shares) at Jun. 29, 2024						61,000,000
Ending Balance at Jun. 29, 2024	47,419	47,432	$ 443	17,649	49,940	$ (18,187)	(2,413)	(12)
Beginning Balance at Dec. 31, 2024	120
Redeemable Noncontrolling Interest [Roll Forward]
Net income/(loss)	8
Other comprehensive income/(loss)	6
Contributions from (distributions to) noncontrolling interests	(8)
Ending Balance at Jun. 28, 2025	126
Balance (in shares) at Dec. 31, 2024			444,000,000
Beginning Balance at Dec. 31, 2024	$ 49,551	49,584	$ 444	17,962	53,102	$ (19,226)	(2,697)	(33)
Treasury stock beginning balance (in shares) at Dec. 31, 2024	63,066,906					63,000,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under stock plans (in shares)			1,000,000			0
Issuance of shares under stock plans	$ 90	90	$ 1	115		$ (26)
Stock-based compensation	156	156		156
Purchases of company common stock (in shares)						4,000,000
Purchases of company common stock	(2,000)	(2,000)				$ (2,000)
Dividends declared	(325)	(325)			(325)
Net income/(loss)	3,122	3,124			3,124			(2)
Other comprehensive income/(loss)	(99)	(99)					(99)
Contributions from (distributions to) noncontrolling interests	(1)							(1)
Excise tax from stock repurchases	$ (17)	(17)				$ (17)
Balance (in shares) at Jun. 28, 2025			444,000,000
Treasury stock ending balance (in shares) at Jun. 28, 2025	66,754,531					67,000,000
Ending Balance at Jun. 28, 2025	$ 50,476	50,512	$ 444	18,232	55,901	$ (21,269)	(2,797)	(35)
Beginning Balance at Mar. 29, 2025	128
Redeemable Noncontrolling Interest [Roll Forward]
Net income/(loss)	3
Other comprehensive income/(loss)	3
Contributions from (distributions to) noncontrolling interests	(8)
Ending Balance at Jun. 28, 2025	126
Balance (in shares) at Mar. 29, 2025			444,000,000
Beginning Balance at Mar. 29, 2025	49,357	49,390	$ 444	18,111	54,447	$ (21,269)	(2,343)	(33)
Treasury stock beginning balance (in shares) at Mar. 29, 2025						67,000,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under stock plans (in shares)			0
Issuance of shares under stock plans	40	40		41		$ (1)
Stock-based compensation	81	81		81
Dividends declared	(163)	(163)			(163)
Net income/(loss)	1,615	1,617			1,617			(2)
Other comprehensive income/(loss)	$ (454)	(453)					(453)
Balance (in shares) at Jun. 28, 2025			444,000,000
Treasury stock ending balance (in shares) at Jun. 28, 2025	66,754,531					67,000,000
Ending Balance at Jun. 28, 2025	$ 50,476	$ 50,512	$ 444	$ 18,232	$ 55,901	$ (21,269)	$ (2,797)	$ (35)