Accrual for chargebacks reflected as a direction reduction to accounts receivable.

No definition available.

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

- Definition

Accrual for rebates recorded as current liability.

+ References

No definition available.

+ Details

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

- Details

Name:	mrk_SummaryOfSignificantAccountingPoliciesLineItems
Namespace Prefix:	mrk_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount charged to advertising expense for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 720

-SubTopic 35

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6420018&loc=d3e36677-107848

+ Details

Name:	us-gaap_AdvertisingExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The carrying amount of capitalized computer software costs net of accumulated amortization as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 985

-SubTopic 20

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6501960&loc=d3e128487-111756

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 985

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6501960&loc=d3e128462-111756

+ Details

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

- Definition

The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

+ Details

Name:	us-gaap_Depreciation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

No definition available.

+ Details

Name:	us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Details

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

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_BuildingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_MachineryAndEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Summary of Accounting Policies - Textual (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Summary Of Significant Accounting Policies [Line Items]
Accrual for chargebacks reflected as direct reduction to Accounts receivable	$ 112,000,000mrk_AccrualForChargebacks	$ 87,000,000mrk_AccrualForChargebacks
Accrual for rebates included in Accrued and other current liabilities	2,000,000,000mrk_AccrualForRebates	1,600,000,000mrk_AccrualForRebates
Depreciation expense	2,500,000,000us-gaap_Depreciation	2,200,000,000us-gaap_Depreciation	2,000,000,000us-gaap_Depreciation
Advertising expenses	2,300,000,000us-gaap_AdvertisingExpense	2,500,000,000us-gaap_AdvertisingExpense	2,800,000,000us-gaap_AdvertisingExpense
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of intangible assets	3 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of intangible assets	20 years
Enterprise wide resource planning system [Member]
Summary Of Significant Accounting Policies [Line Items]
Unamortized capitalized software costs	$ 505,000,000	$ 548,000,000
Enterprise wide resource planning system [Member] \| Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of intangible assets	6 years
Enterprise wide resource planning system [Member] \| Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of intangible assets	10 years
Capitalized Software [Member] \| Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of intangible assets	3 years
Capitalized Software [Member] \| Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of intangible assets	5 years
Machinery and Equipment [Member] \| Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of property, plant and equipment	3 years
Machinery and Equipment [Member] \| Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of property, plant and equipment	15 years
Building [Member] \| Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of property, plant and equipment	10 years
Building [Member] \| Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of property, plant and equipment	50 years