Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2015	Jan. 27, 2016	Jun. 30, 2015
Document 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-K
Document Period End Date	Dec. 31, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		239,590,579
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 16,891,929,000