v3.26.1
Intangible Assets and Goodwill (Schedule of Components of Intangible Assets) (Details) - USD ($)
$ in Millions
Jun. 30, 2026
Dec. 31, 2025
Intangible Assets [Line Items]    
Assigned Value $ 4,831.1 $ 4,839.4
Accumulated Amortization (2,786.5) (2,678.7)
Net Book Value 2,044.6 2,160.7
Total intangible assets – other, net 2,494.6 2,610.7
Trading products 17,175.3 17,175.3
Trade names    
Intangible Assets [Line Items]    
Trade names 450.0 450.0
Clearing firm, market data and other customer relationships    
Intangible Assets [Line Items]    
Assigned Value 4,695.3 4,703.0
Accumulated Amortization (2,661.8) (2,557.5)
Net Book Value 2,033.5 2,145.5
Technology-related intellectual property    
Intangible Assets [Line Items]    
Assigned Value 62.5 62.5
Accumulated Amortization (62.5) (62.5)
Net Book Value 0.0 0.0
Other    
Intangible Assets [Line Items]    
Assigned Value 73.3 73.9
Accumulated Amortization (62.2) (58.7)
Net Book Value $ 11.1 $ 15.2