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Earnings Per Share (Net Income Attributable To CME Group) (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Earnings Per Share [Abstract]    
Dividends, Preferred Stock $ (5.7) $ (5.3)
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic (6.3) (5.5)
Net Income Attributable to Common Shareholders of CME Group $ 944.2 $ 844.4
Basic (in shares) 359,613 359,258
Effect of stock options, restricted stock and performance shares 614 575
Diluted (in shares) 360,227 359,833
Earnings per common share, basic (in dollars per share) $ 2.63 $ 2.35
Earnings per common share, diluted (in dollars per share) $ 2.62 $ 2.35