Performance Bonds and Guaranty Fund Contributions (Notes)	9 Months Ended
Sep. 30, 2015
Performance Bonds and Guaranty Fund Contributions [Abstract]
Performance Bonds and Guaranty Fund Contributions [Text Block]	Performance Bonds and Guaranty Fund Contributions Performance Bonds and Guaranty Fund Contributions. At September 30, 2015, performance bonds and guaranty fund contribution assets on the consolidated balance sheets include cash and U.S. Treasury securities with maturity dates of 90 days or less. U.S. Treasury securities are purchased by CME, at its discretion, using cash collateral. The benefits, including interest earned, and risks of ownership accrue to CME. Interest earned is included in investment income on the consolidated statements of income. At September 30, 2015, the amortized cost and fair value of the U.S. Treasury securities were both $15.1 billion. The U.S. Treasury securities will mature in the fourth quarter of 2015. Performance bonds and guaranty fund contribution assets also include overnight reverse repurchase agreements that were purchased by CME, at its discretion, using cash collateral. The fair value of the overnight securities under the reverse repurchase agreements was $1.8 billion at September 30, 2015. Clearing House Contract Settlement. CME Clearing and CMECE mark-to-market open positions for all futures and options contracts twice a day (once a day for CME's cleared-only credit default swap and interest rate swap contracts). Based on values derived from the mark-to-market process, CME Clearing and CMECE require payments from clearing firms whose positions have lost value and make payments to clearing firms whose positions have gained value. Under the extremely unlikely scenario of simultaneous default by every clearing firm who has open positions with unrealized losses, the maximum exposure related to positions other than cleared-only credit default and interest rate swap contracts would be one half day of changes in fair value of all open positions, before considering the clearing houses' ability to access defaulting clearing firms' collateral deposits. For CME's cleared-only credit default swap and interest rate swap contracts, the maximum exposure related to CME Clearing's guarantee would be one full day of changes in fair value of all open positions, before considering CME Clearing's ability to access defaulting clearing firms' collateral. During the first nine months of 2015, CME Clearing and CMECE transferred an average of approximately $4.1 billion a day through their clearing systems for settlement from clearing firms whose positions had lost value to clearing firms whose positions had gained value. CME Clearing and CMECE reduce their guarantee exposure through initial and maintenance performance bond requirements and mandatory guaranty fund contributions. The company believes that its guarantee liability is immaterial and therefore has not recorded any liability at September 30, 2015.

Performance Bonds and Guaranty Fund Contributions

Performance Bonds and Guaranty Fund Contributions. At September 30, 2015, performance bonds and guaranty fund contribution assets on the consolidated balance sheets include cash and U.S. Treasury securities with maturity dates of 90 days or less. U.S. Treasury securities are purchased by CME, at its discretion, using cash collateral. The benefits, including interest earned, and risks of ownership accrue to CME. Interest earned is included in investment income on the consolidated statements of income. At September 30, 2015, the amortized cost and fair value of the U.S. Treasury securities were both $15.1 billion. The U.S. Treasury securities will mature in the fourth quarter of 2015. Performance bonds and guaranty fund contribution assets also include overnight reverse repurchase agreements that were purchased by CME, at its discretion, using cash collateral. The fair value of the overnight securities under the reverse repurchase agreements was $1.8 billion at September 30, 2015.

Clearing House Contract Settlement. CME Clearing and CMECE mark-to-market open positions for all futures and options contracts twice a day (once a day for CME's cleared-only credit default swap and interest rate swap contracts). Based on values derived from the mark-to-market process, CME Clearing and CMECE require payments from clearing firms whose positions have lost value and make payments to clearing firms whose positions have gained value. Under the extremely unlikely scenario of simultaneous default by every clearing firm who has open positions with unrealized losses, the maximum exposure related to positions other than cleared-only credit default and interest rate swap contracts would be one half day of changes in fair value of all open positions, before considering the clearing houses' ability to access defaulting clearing firms' collateral deposits. For CME's cleared-only credit default swap and interest rate swap contracts, the maximum exposure related to CME Clearing's guarantee would be one full day of changes in fair value of all open positions, before considering CME Clearing's ability to access defaulting clearing firms' collateral. During the first nine months of 2015, CME Clearing and CMECE transferred an average of approximately $4.1 billion a day through their clearing systems for settlement from clearing firms whose positions had lost value to clearing firms whose positions had gained value. CME Clearing and CMECE reduce their guarantee exposure through initial and maintenance performance bond requirements and mandatory guaranty fund contributions. The company believes that its guarantee liability is immaterial and therefore has not recorded any liability at September 30, 2015.