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Contingencies - Environmental - Narrative (Details) € in Thousands, $ in Thousands	1 Months Ended	3 Months Ended
	Jan. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2018 EUR (€)
Loss Contingencies [Line Items]
Loss on settlement	$ (115,000)
Oss Netherlands
Loss Contingencies [Line Items]
Fine for alleged environmental violation		$ 235
Loss on settlement | €			€ 400

X

- Definition

Fine For Alleged Environmental Violation

+ References

No definition available.

+ Details

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

X

- Definition

Amount of gain (loss) recognized in settlement of litigation and insurance claims. Excludes claims within an insurance entity's normal claims settlement process.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

+ Details

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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
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X

- Details

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Namespace Prefix:
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Balance Type:
Period Type: