CONDENSED CONSOLIDATED STATEMENT OF OPERATIONS - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2026	Mar. 31, 2025
Income Statement [Abstract]
Sales	$ 16,286	$ 15,529
Costs, Expenses and Other
Cost of sales	4,195	3,419
Selling, general and administrative	2,700	2,552
Research and development	12,592	3,621
Restructuring costs	195	69
Other (income) expense, net	138	(35)
Total Costs, Expenses and Other	19,820	9,626
(Loss) Income Before Taxes	(3,534)	5,903
Income Tax Provision	709	818
Net (Loss) Income	(4,243)	5,085
Less: Net (Loss) Income Attributable to Noncontrolling Interests	(3)	6
Net (Loss) Income Attributable to Merck & Co., Inc.	$ (4,240)	$ 5,079
Basic (Loss) Earnings per Common Share Attributable to Merck & Co., Inc. Common Shareholders (in dollars per share)	$ (1.72)	$ 2.01
(Loss) Earnings per Common Share Assuming Dilution Attributable to Merck & Co., Inc. Common Shareholders (in dollars per share)	$ (1.72)	$ 2.01

Total of cost of sales, operating expenses and nonoperating income or expense.

No definition available.

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Namespace Prefix:	mrk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The aggregate costs related to goods produced and sold and services rendered by an entity during the reporting period. This excludes costs incurred during the reporting period related to financial services rendered and other revenue generating activities.