Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2015	Oct. 14, 2015
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2015
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	2015
Entity Registrant Name	CME GROUP INC.
Entity Central Index Key	0001156375
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Class A Common Stock [Member]
Entity Common Stock, Shares Outstanding		338,233,253
Class B Common Stock, Class B-1 [Member]
Entity Common Stock, Shares Outstanding		625
Class B Common Stock, Class B-2 [Member]
Entity Common Stock, Shares Outstanding		813
Class B Common Stock, Class B-3 [Member]
Entity Common Stock, Shares Outstanding		1,287
Class B Common Stock, Class B-4 [Member]
Entity Common Stock, Shares Outstanding		413