Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Net income	$ 218.9	$ 315.0	$ 738.6	$ 1,067.7
Other comprehensive income, net of tax
Net unrealized holding gains arising during the period	109.5	(188.0)	84.4	122.6
Investment securities, income tax benefit (expense)	(73.9)	73.5	(58.8)	(9.1)
Investment securities, net	35.6	(114.5)	25.6	113.5
Net change in defined benefit plans arising during the period	0	0	0.5	(3.4)
Amortization of net actuarial (gains) losses included in pension expense	0.7	0.5	1.9	1.3
Defined benefit plans, income tax benefit (expense)	(0.3)	(0.3)	(0.9)	0.8
Defined benefit plans, net	0.4	0.2	1.5	(1.3)
Net unrealized holding losses arising during the period	(54.4)	0	(54.4)	0
Amortization of effective portion of loss on cash flow hedge	0.2	0.2	0.4	0.8
Derivative instruments, income tax benefit (expense)	19.8	(0.1)	19.8	(0.3)
Derivative instruments, net	(34.4)	0.1	(34.2)	0.5
Foreign currency translation adjustment	5.9	(3.8)	5.5	96.1
Reclassification adjustment for loss included in net income	0	0	18.4	0
Foreign currency translation, income tax benefit (expense)	(2.1)	1.5	(8.7)	(12.8)
Foreign currency translation, net	3.8	(2.3)	15.2	83.3
Other comprehensive income, net of tax	5.4	(116.5)	8.1	196.0
Comprehensive income	224.3	198.5	746.7	1,263.7
Less: comprehensive income attributable to redeemable non-controlling interest	0.9	(1.1)	9.1	1.3
Comprehensive income attributable to CME Group	$ 223.4	$ 199.6	$ 737.6	$ 1,262.4