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Contingencies and Environmental Liabilities - Propecia/Proscar Litigation - Narrative (Details) - Propecia/Proscar $ in Millions	Apr. 09, 2018 USD ($)	Dec. 31, 2018 legalmatter
Loss Contingencies [Line Items]
Settlement awarded to other party | $	$ 4.3
Plaintiff participation in litigation settlement (as percent)	95.00%
Loss contingency, pending claims number | legalmatter		25

X

- Definition

Percentage of claims participating in litigation settlement.

+ References

No definition available.

+ Details

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Namespace Prefix:	mrk_
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X

- Definition

Amount awarded to other party in judgment or settlement of litigation.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- 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

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
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X

- Definition

Number of pending claims pertaining to a loss contingency.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14435-108349

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	na
Period Type:	instant

X

- Details

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Namespace Prefix:
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Balance Type:
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