Consolidated Statements Of Shareholders' Equity - USD ($) shares in Thousands, $ in Millions	Total	Common Stock And Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Parent [Member]	Noncontrolling Interest [Member]	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]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 21,160.5
Balance (in shares) at Dec. 31, 2013								333,852		3
Balance at Dec. 31, 2013		$ 17,508.2	$ 3,494.6	$ 152.0	$ 21,154.8
Stockholders' Equity Attributable to Noncontrolling Interest at Dec. 31, 2013						$ 5.7
Net Income Attributable to CME Group	820.6		820.6		820.6
Net Income (Loss) Attributable to Noncontrolling Interest	(0.2)					(0.2)
Net income	820.4
Other Comprehensive Income (Loss), Net of Tax	(21.5)			(21.5)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(21.5)			(21.5)	(21.5)
Dividends on common stock per share	(473.2)		(473.2)		(473.2)
Adjustments to Additional Paid in Capital, Other	(7.0)					(5.5)
Exercise of stock options (in shares)								590
Exercise of stock options	26.6	26.6			26.6
Excess tax benefits from option exercises and restricted stock vesting	3.3	3.3			3.3
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures								496
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures	(16.2)	(16.2)			(16.2)
Stock Issued To Related Parties During Period Shares								34
Stock Issued To Related Parties During Period Value	2.4	2.4			2.4
Stock Issued During Period, Shares, Employee Stock Purchase Plans								13
Stock Issued During Period, Value, Employee Stock Purchase Plan	0.9	0.9			0.9
Stock Granted, Value, Share-based Compensation, Gross	40.9	40.9			40.9
Stockholders' Equity Attributable to Noncontrolling Interest at Sep. 30, 2014						$ 0.0
Balance (in shares) at Sep. 30, 2014								334,985		3
Balance at Sep. 30, 2014		17,564.6	3,842.0	130.5	21,537.1
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	21,537.1
Balance (in shares) at Dec. 31, 2014							335,452	335,452	3	3
Balance at Dec. 31, 2014	20,923.5	17,600.0	3,317.3	6.2	20,923.5
Net Income Attributable to CME Group	955.3		955.3		955.3
Net Income (Loss) Attributable to Noncontrolling Interest	0.0
Other Comprehensive Income (Loss), Net of Tax	(100.8)			(100.8)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent					(100.8)
Dividends on common stock per share			(500.8)		(500.8)
Adjustments to Additional Paid in Capital, Other		9.3			9.3
Exercise of stock options (in shares)								798
Exercise of stock options		51.8			51.8
Excess tax benefits from option exercises and restricted stock vesting		6.7			6.7
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures								450
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures		(16.8)			(16.8)
Stock Issued To Related Parties During Period Shares								26
Stock Issued To Related Parties During Period Value		2.4			2.4
Stock Issued During Period, Shares, Employee Stock Purchase Plans								10
Stock Issued During Period, Value, Employee Stock Purchase Plan		1.0			1.0
Stock Granted, Value, Share-based Compensation, Gross		45.2			45.2
Balance (in shares) at Sep. 30, 2015							336,736	336,736	3	3
Balance at Sep. 30, 2015	$ 21,376.8	$ 17,699.6	$ 3,771.8	$ (94.6)	$ 21,376.8