GOODWILL, INTANGIBLE ASSETS, NET, AND DIGITAL ASSETS HELD - Goodwill by segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Goodwill
Balance at beginning of the period	$ 3,124.2	$ 3,140.6
Adjustments		0.0
Changes in foreign currency exchange rates	26.3	(16.4)
Balance at end of the period	3,150.5	3,124.2
Options
Goodwill
Balance at beginning of the period	306.0	305.8
Adjustments		0.2
Changes in foreign currency exchange rates	0.0	0.0
Balance at end of the period	306.0	306.0
North American Equities
Goodwill
Balance at beginning of the period	1,990.8	2,004.4
Adjustments		(0.8)
Changes in foreign currency exchange rates	7.3	(12.8)
Balance at end of the period	1,998.1	1,990.8
Europe and Asia Pacific
Goodwill
Balance at beginning of the period	560.0	563.2
Adjustments		0.4
Changes in foreign currency exchange rates	19.0	(3.6)
Balance at end of the period	579.0	560.0
Global FX
Goodwill
Balance at beginning of the period	267.4	267.2
Adjustments		0.2
Changes in foreign currency exchange rates	0.0	0.0
Balance at end of the period	267.4	$ 267.4
Futures
Goodwill
Balance at end of the period	$ 0.0