Restructuring (Details 1) (USD $) In Millions	9 Months Ended
Sep. 30, 2011
2008 Global Restructuring Program [Member] \| Separation Costs [Member]
Charges and spending relating to Merger Restructuring Program and 2008 Restructuring Program activities
Restructuring reserve, beginning balance	$ 196
Expense	(3)
(Payments) receipts, net	(53)
Non-cash activity	0
Restructuring reserve, ending balance	140
Merger Restructuring Program [Member] \| Separation Costs [Member]
Charges and spending relating to Merger Restructuring Program and 2008 Restructuring Program activities
Restructuring reserve, beginning balance	859
Expense	670
(Payments) receipts, net	(417)
Non-cash activity	0
Restructuring reserve, ending balance	1,112
2008 Global Restructuring Program [Member] \| Other [Member]
Charges and spending relating to Merger Restructuring Program and 2008 Restructuring Program activities
Restructuring reserve, beginning balance	0
Expense	12
(Payments) receipts, net	(11)
Non-cash activity	(1)
Restructuring reserve, ending balance	0
Merger Restructuring Program [Member] \| Other [Member]
Charges and spending relating to Merger Restructuring Program and 2008 Restructuring Program activities
Restructuring reserve, beginning balance	64
Expense	99
(Payments) receipts, net	(121)
Non-cash activity	7
Restructuring reserve, ending balance	49
2008 Global Restructuring Program [Member]
Charges and spending relating to Merger Restructuring Program and 2008 Restructuring Program activities
Restructuring reserve, beginning balance	196
Expense	25
(Payments) receipts, net	(64)
Non-cash activity	(17)
Restructuring reserve, ending balance	140
2008 Global Restructuring Program [Member] \| Accelerated Depreciation [Member]
Charges and spending relating to Merger Restructuring Program and 2008 Restructuring Program activities
Restructuring reserve, beginning balance	0
Expense	16
(Payments) receipts, net	0
Non-cash activity	(16)
Restructuring reserve, ending balance	0
Merger Restructuring Program [Member]
Charges and spending relating to Merger Restructuring Program and 2008 Restructuring Program activities
Restructuring reserve, beginning balance	923
Expense	1,176
(Payments) receipts, net	(538)
Non-cash activity	(400)
Restructuring reserve, ending balance	1,161
Merger Restructuring Program [Member] \| Accelerated Depreciation [Member]
Charges and spending relating to Merger Restructuring Program and 2008 Restructuring Program activities
Restructuring reserve, beginning balance	0
Expense	407
(Payments) receipts, net	0
Non-cash activity	(407)
Restructuring reserve, ending balance	$ 0

Noncash activity affecting the restructuring reserve, including accelerated depreciation.

Name:	mrk_RestructuringReserveNoncashActivity
Namespace Prefix:	mrk
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Carrying amount (including both current and noncurrent portions of the accrual) as of the balance sheet date pertaining to a specified type of cost associated with exit from or disposal of business activities or restructuring pursuant to a duly authorized plan.

+ References

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

-Publisher FASB

-Name Emerging Issues Task Force (EITF)

-Number 95-3

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 5

-Section P

-Subsection 3, 4

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 420

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SAB TOPIC 5.P.4(b))

-URI http://asc.fasb.org/extlink&oid=6394695&loc=d3e140904-122747

+ Details

Name:	us-gaap_RestructuringReserve
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Reserve increase representing the amount charged against earnings in the period for a specified incurred and estimated type of cost associated with exit from or disposal of business activities or restructuring pursuant to a duly authorized plan.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 146

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 420

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)(2)

-URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869

+ Details

Name:	us-gaap_RestructuringReservePeriodExpense
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ Details

Name:	us-gaap_RestructuringReserveRollForward
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of cash paid in the period to fully or partially settle a specified, previously accrued type of restructuring cost.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 420

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SAB TOPIC 5.P.4(b)(2))

-URI http://asc.fasb.org/extlink&oid=6394695&loc=d3e140904-122747

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 420

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b) (2)

-URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Emerging Issues Task Force (EITF)

-Number 95-3

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 5

-Section P

-Subsection 3, 4

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 146

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Name:	us-gaap_RestructuringReserveSettledWithCash
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration