Document And Entity Information	9 Months Ended
	Sep. 30, 2012	Oct. 17, 2012 Class A Common Stock [Member]	Oct. 17, 2012 Class B Common Stock, Class B-1 [Member]	Oct. 17, 2012 Class B Common Stock, Class B-2 [Member]	Oct. 17, 2012 Class B Common Stock, Class B-3 [Member]	Oct. 17, 2012 Class B Common Stock, Class B-4 [Member]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2012
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	2012
Entity Registrant Name	CME GROUP INC.
Entity Central Index Key	0001156375
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		333,384,469	625	813	1,287	413