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Organization and Business (Details) (USD $)
In Millions, unless otherwise specified
6 Months Ended 12 Months Ended
Jun. 30, 2013
Dec. 31, 2014
Dec. 31, 2012
Apr. 30, 2013
Mar. 18, 2010
Jun. 30, 2012
Business Acquisition [Line Items]            
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests $ 80.0us-gaap_MinorityInterestDecreaseFromRedemptions   $ 5.8us-gaap_MinorityInterestDecreaseFromRedemptions      
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage   51.00%us-gaap_VariableInterestEntityOwnershipPercentage        
S&P/Dow Jones Indices LLC [Member]            
Business Acquisition [Line Items]            
Equity Method Investment, Ownership Percentage       27.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_BusinessAcquisitionAxis
= cme_SpdowJonesIndicesLlcMember
   
Dow Jones [Member]            
Business Acquisition [Line Items]            
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners         10.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
/ dei_LegalEntityAxis
= cme_DowJonesMember
 
CME Group net of non-controlling interest [Member]            
Business Acquisition [Line Items]            
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners   24.40%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
/ dei_LegalEntityAxis
= cme_CmeGroupNetOfNonControllingInterestMember
      24.40%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
/ dei_LegalEntityAxis
= cme_CmeGroupNetOfNonControllingInterestMember