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Long-Term Investments (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended 1 Months Ended 12 Months Ended 12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Dec. 31, 2011
BM&F [Member]
Dec. 31, 2011
Bolsa Mexicana De Valores, S A B De C V [Member]
Dec. 31, 2011
Bursa Malaysia Derivatives Berhad [Member]
Dec. 31, 2011
DME Holdings [Member]
Dec. 31, 2009
DME Holdings [Member]
Dec. 31, 2011
GX Holdings [Member]
Dec. 31, 2009
IMAREX [Member]
Dec. 31, 2011
IMAREX [Member]
Investment ownership interest       5.00% 2.00%            
Fair value of investment   $ 46.0   $ 527.7 $ 18.8 $ 27.4 $ 2.1   $ 4.1   $ 6.3
Loan provided to DME             3.0        
Cost-basis value of investment       262.9 17.3           3.8
Ownership percentage           25.00% 28.00%   40.00%   15.00%
Investment impairment charges $ 0 $ 2.2 $ 46.0         $ 23.6   $ 22.4