Master Trust - Schedule of Master Trust Net Assets (Details) - EBP 061 - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
EBP, Master Trust [Line Items]
Investments, at fair value	$ 244,610	$ 228,820
Net assets available for benefits	246,925	231,602
Master Trust
EBP, Master Trust [Line Items]
Investments, at fair value	16,857,006	15,633,706
Accrued interest and dividends	15,877	17,180
Other net assets	8,648	4,994
Net assets available for benefits	16,881,531	15,655,880
Master Trust \| Registered investment companies (mutual funds)
EBP, Master Trust [Line Items]
Investments, at fair value	97,747	500,106
Master Trust \| Common/collective trusts
EBP, Master Trust [Line Items]
Investments, at fair value	12,677,091	11,107,463
Master Trust \| Equity securities
EBP, Master Trust [Line Items]
Investments, at fair value	2,307,397	2,244,340
Master Trust \| Fixed income securities
EBP, Master Trust [Line Items]
Investments, at fair value	406,994	386,182
Master Trust \| Self-directed brokerage accounts
EBP, Master Trust [Line Items]
Investments, at fair value	459,800	368,784
Master Trust \| Merck common stock
EBP, Master Trust [Line Items]
Investments, at fair value	907,977	1,026,831
Puerto Rico
EBP, Master Trust [Line Items]
Accrued interest and dividends	389	388
Other net assets	143	70
Net assets available for benefits	244,537	228,777
Puerto Rico \| Registered investment companies (mutual funds)
EBP, Master Trust [Line Items]
Investments, at fair value	1,674	7,602
Puerto Rico \| Common/collective trusts
EBP, Master Trust [Line Items]
Investments, at fair value	171,262	151,225
Puerto Rico \| Equity securities
EBP, Master Trust [Line Items]
Investments, at fair value	33,498	32,895
Puerto Rico \| Fixed income securities
EBP, Master Trust [Line Items]
Investments, at fair value	7,217	6,655
Puerto Rico \| Self-directed brokerage accounts
EBP, Master Trust [Line Items]
Investments, at fair value	1,048	431
Puerto Rico \| Merck common stock
EBP, Master Trust [Line Items]
Investments, at fair value	$ 29,306	$ 29,511

Fair value of investment held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Includes, but is not limited to, derivative, investment measured at net asset value per share as practical expedient, and insurance contract not meeting fully-benefit responsive investment criteria.

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