Collaborative Arrangement, Future Fixed Upfront Payments From Collaborative Partner

No definition available.

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

- Definition

Collaborative Arrangement, Milestone Payment From Collaborative Partner

+ References

No definition available.

+ Details

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

- Definition

Collaborative Arrangement, Rights And Obligations, Maximum Aggregate Regulatory Milestone Payments

+ References

No definition available.

+ Details

Name:	mrk_CollaborativeArrangementRightsAndObligationsMaximumAggregateRegulatoryMilestonePayments
Namespace Prefix:	mrk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Collaborative Arrangement, Rights And Obligations, Maximum Aggregate Sales-Based Milestone Payments

+ References

No definition available.

+ Details

Name:	mrk_CollaborativeArrangementRightsAndObligationsMaximumAggregateSalesBasedMilestonePayments
Namespace Prefix:	mrk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Collaborative Arrangement, Rights and Obligations, Milestone Payments, Sales-Based

+ References

No definition available.

+ Details

Name:	mrk_CollaborativeArrangementRightsAndObligationsMilestonePaymentsSalesBased
Namespace Prefix:	mrk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Collaborative Arrangement, Royalties On Net Sales, Percent

+ References

No definition available.

+ Details

Name:	mrk_CollaborativeArrangementRoyaltiesOnNetSalesPercent
Namespace Prefix:	mrk_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Collaborative Arrangement, Upfront Payments Received Recognized As Revenue

+ References

No definition available.

+ Details

Name:	mrk_CollaborativeArrangementUpfrontPaymentsReceivedRecognizedAsRevenue
Namespace Prefix:	mrk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 808
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479402/808-10-50-1

+ Details

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

- Definition

Amount, after accumulated amortization, of finite-lived intangible asset. Excludes goodwill and capitalized cost for software to be sold, leased, or marketed.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 350
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482665/350-30-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 926
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483154/926-20-50-5

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	srt_ProductOrServiceAxis=mrk_LynparzaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=mrk_LicensesAndOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=mrk_KoselugoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=mrk_AstraZenecaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=us-gaap_CollaborativeArrangementTransactionWithPartyToCollaborativeArrangementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=mrk_AllianceRevenueKoselugoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementScenarioAxis=srt_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Collaborative Arrangements - AstraZeneca PLC - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended						6 Months Ended
	Feb. 28, 2026	Sep. 30, 2028	Mar. 31, 2028	Sep. 30, 2027	Mar. 31, 2027	Jun. 30, 2026	Sep. 30, 2025	Jun. 30, 2026	Jun. 30, 2025	Dec. 31, 2025
Lynparza \| Licenses and Other
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Finite-lived intangible assets						$ 681,000,000		$ 681,000,000
Koselugo \| Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of royalties on net sales percent								6.00%
Koselugo \| Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of royalties on net sales percent								7.00%
Koselugo \| Licenses and Other
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Finite-lived intangible assets						33,000,000		$ 33,000,000
AstraZeneca \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront payments recognized as revenue								150,000,000
Sales based milestone payments									$ 700,000,000
AstraZeneca \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Alliance revenue - Koselugo
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront payments recognized as revenue	$ 150,000,000						$ 150,000,000
Aggregate, regulatory milestones payments, maximum										$ 175,000,000
Collaborative arrangement, milestone payment						50,000,000
Sales milestone payments						$ 235,000,000		$ 235,000,000
AstraZeneca \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Alliance revenue - Koselugo \| Forecast
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Future fixed upfront payments received			$ 100,000,000		$ 150,000,000
Collaborative arrangement, milestone payment		$ 75,000,000		$ 50,000,000
AstraZeneca \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Lynparza
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate, regulatory milestones payments, maximum									0
Sales milestone payments									2,000,000,000.0
Sales based milestone payments									600,000,000
AstraZeneca \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Koselugo
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Sales based milestone payments									$ 100,000,000