Intangible Assets And Goodwill (Goodwill Activity) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Goodwill [Line Items]
Goodwill, Acquired During Period	$ 17.7	$ 0
Goodwill, Written off Related to Sale of Business Unit	(463.4)		0
Total Goodwill, beginning balance	7,984.0	7,983.6	7,983.6
Other Activity	0		0.4	[1]
Total Goodwill, ending balance	7,538.3		7,984.0
CBOT Holdings, Inc. [Member]
Goodwill [Line Items]
Goodwill, Acquired During Period	0	0
Goodwill, Written off Related to Sale of Business Unit	0		0
Total Goodwill, beginning balance	5,035.7	5,035.7	5,035.7
Other Activity	0		0	[1]
Total Goodwill, ending balance	5,035.7		5,035.7
NYMEX Holdings, Inc. [Member]
Goodwill [Line Items]
Goodwill, Acquired During Period	0	0
Goodwill, Written off Related to Sale of Business Unit	0		0
Total Goodwill, beginning balance	2,462.2	2,462.3	2,462.3
Other Activity	0		(0.1)	[1]
Total Goodwill, ending balance	2,462.2		2,462.2
Index Services [Member]
Goodwill [Line Items]
Goodwill, Acquired During Period	0	0
Goodwill, Written off Related to Sale of Business Unit	(434.5)		0
Total Goodwill, beginning balance	434.5	435.6	435.6
Other Activity	0		(1.1)	[1]
Total Goodwill, ending balance	0		434.5
Other [Member]
Goodwill [Line Items]
Goodwill, Acquired During Period	17.7	0
Goodwill, Written off Related to Sale of Business Unit	(28.9)		0
Total Goodwill, beginning balance	51.6	50.0	50.0
Other Activity	0		1.6	[1]
Total Goodwill, ending balance	$ 40.4		$ 51.6

[1] Other activity includes adjustments to tax contingencies, the recognition of excess tax benefits upon exercise of stock options and foreign currency translation adjustments.