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Intangible Assets and Goodwill Intangible Assets and Goodwill (Components of Goodwill) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Goodwill [Line Items]      
Goodwill $ 10,495.3 $ 10,482.5  
CBOT [Member]      
Goodwill [Line Items]      
Goodwill 5,066.4 5,066.4 $ 5,066.4
Goodwill, Other Increase (Decrease) 0.0 0.0  
NYMEX [Member]      
Goodwill [Line Items]      
Goodwill 2,462.2 2,462.2 2,462.2
Goodwill, Other Increase (Decrease) 0.0 0.0  
NEX [Member]      
Goodwill [Line Items]      
Goodwill 2,930.8 2,913.5 2,959.0
Goodwill, Other Increase (Decrease) 17.3 (45.5)  
Other CME Segments      
Goodwill [Line Items]      
Goodwill 35.9 40.4 40.4
Goodwill, Other Increase (Decrease) (4.5) 0.0  
CME Group Inc.      
Goodwill [Line Items]      
Goodwill 10,495.3 10,482.5 $ 10,528.0
Goodwill, Other Increase (Decrease) $ 12.8 $ (45.5)