Consolidated Statements Of Shareholders' Equity (USD $) In Millions, except Share data in Thousands	Total USD ($)	Common Stock And Additional Paid-In Capital [Member] USD ($)	Retained Earnings [Member] USD ($)	Accumulated Other Comprehensive Income (Loss) [Member] USD ($)	Class A Common Stock [Member]	Class A Common Stock [Member] Common Stock And Additional Paid-In Capital [Member]	Class B Common Stock [Member]	Class B Common Stock [Member] Common Stock And Additional Paid-In Capital [Member]
Balance at Dec. 31, 2010	$ 20,060.1	$ 17,278.4	$ 2,885.8	$ (104.1)
Balance (in shares) at Dec. 31, 2010						334,245		3
Net Income Attributable to CME Group	1,066.4		1,066.4
Other comprehensive income attributable to CME Group	196.0			196.0
Dividends on common stock per share	(280.6)		(280.6)
Stock Repurchased During Period, Shares						(4,048)
Stock Repurchased During Period, Value	(220.4)	(220.4)
Exercise of stock options (in shares)						154
Exercise of stock options	5.2	5.2
Excess tax benefits from option exercises and restricted stock vesting	0.7	0.7
Vesting of issued restricted Class A common stock (in shares)						201
Vesting of issued restricted Class A common stock	(3.7)	(3.7)
Shares issued to Board of Directors (in shares)						41
Shares issued to Board of Directors	2.3	2.3
Shares issued under Employee Stock Purchase Plan (in shares)						14
Shares issued under Employee Stock Purchase Plan	0.8	0.8
Stock-based compensation	37.5	37.5
Balance at Sep. 30, 2011	20,864.3	17,100.8	3,671.6	91.9
Balance (in shares) at Sep. 30, 2011						330,607		3
Balance at Dec. 31, 2011	21,552.0	17,115.8	4,324.6	111.6
Balance (in shares) at Dec. 31, 2011					330,653	330,653	3	3
Net Income Attributable to CME Group	729.5		729.5
Other comprehensive income attributable to CME Group	8.1			8.1
Dividends on common stock per share	(645.5)		(645.5)
Exercise of stock options (in shares)						632
Exercise of stock options	19.2	19.2
Excess tax benefits from option exercises and restricted stock vesting	3.7	3.7
Vesting of issued restricted Class A common stock (in shares)						348
Vesting of issued restricted Class A common stock	(9.8)	(9.8)
Shares issued to Board of Directors (in shares)						40
Shares issued to Board of Directors	2.1	2.1
Shares issued under Employee Stock Purchase Plan (in shares)						13
Shares issued under Employee Stock Purchase Plan	0.7	0.7
Stock-based compensation	48.8	48.8
Balance at Sep. 30, 2012	$ 21,708.8	$ 17,180.5	$ 4,408.6	$ 119.7
Balance (in shares) at Sep. 30, 2012					331,686	331,686	3	3