Document and Entity Information	9 Months Ended
	Sep. 30, 2011	Oct. 10, 2011
Entity Information [Line Items]
Entity Registrant Name	OMNICOM GROUP INC.
Entity Central Index Key	0000029989
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2011
Document Fiscal Year Focus	2011
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		275,874,000