Consolidated Statement of Income - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Sales	$ 47,994	$ 46,840	$ 42,294
Costs, Expenses and Other
Cost of sales	15,485	14,112	13,509
Selling, general and administrative	10,468	10,615	10,102
Research and development	13,558	9,872	9,752
Restructuring costs	578	638	632
Other (income) expense, net	(886)	139	(402)
Total costs, expenses and other	39,203	35,376	33,593
Income Before Taxes	8,791	11,464	8,701
Taxes on Income	1,709	1,687	2,508
Net Income	7,082	9,777	6,193
Less: Net Income (Loss) Attributable to Noncontrolling Interests	15	(66)	(27)
Net Income Attributable to Merck & Co., Inc.	$ 7,067	$ 9,843	$ 6,220
Basic Earnings per Common Share Attributable to Merck & Co., Inc. Common Shareholders (in dollars per share)	$ 2.79	$ 3.84	$ 2.34
Earnings per Common Share Assuming Dilution Attributable to Merck & Co., Inc. Common Shareholders (in dollars per share)	$ 2.78	$ 3.81	$ 2.32

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

No definition available.

Name:	mrk_CostsExpensesAndOther
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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 924
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 11.L)
-URI http://asc.fasb.org/extlink&oid=6472922&loc=d3e499488-122856

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.2(a),(d))
-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227