Name:	omc_AdjustmenttoAdditionalPaidInCapitalConversionofConvertibleDebt
Namespace Prefix:	omc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

The amount of current taxes payable reclassified from long-term deferred tax liability, representing the excess of the accreted value of the converted notes for income tax purposes over the conversion value.

No definition available.

Name:	omc_CurrentTaxesPayableConversionofConvertibleDebt
Namespace Prefix:	omc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Income tax benefit related to merger expenses previously incurred.

No definition available.

Name:	omc_Incometaxbenefitmergerexpenses
Namespace Prefix:	omc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	omc_IncomeTaxesAbstract
Namespace Prefix:	omc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Unrecognized Tax Benefit

-URI http://asc.fasb.org/extlink&oid=6527854

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15A

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319

Name:	us-gaap_UnrecognizedTaxBenefits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319