FAIR VALUE MEASUREMENT - Changes in fair value of Level 3 financial liabilities (Details) - Level 3 - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Assets:
Balance at Beginning of Period	$ 0.0	$ 6.2	$ 0.0
(Losses) Gains during Period	0.8	(0.8)
Adjustments	0.0	0.0
Additions	0.0	7.0
Settlements	(7.0)	0.0
Foreign Currency Translation	0.0	0.0
Liabilities:
Balance at Beginning of Period	0.0	36.4
Losses (Gains) during Period		(0.4)
Adjustments		(16.2)
Additions		0.0
Settlements		(19.9)
Foreign Currency Translation		0.1
Balance at End of Period		0.0
Contingent consideration liabilities
Liabilities:
Balance at Beginning of Period	0.0	11.8
Losses (Gains) during Period		2.0
Adjustments		0.0
Additions		0.0
Settlements		(13.9)
Foreign Currency Translation		0.1
Balance at End of Period		0.0
Cboe Digital restricted common units liability
Liabilities:
Balance at Beginning of Period	0.0	18.7
Losses (Gains) during Period		(1.0)
Adjustments		(12.1)
Additions		0.0
Settlements		(5.6)
Foreign Currency Translation		0.0
Balance at End of Period		0.0
Cboe Digital warrant liability
Liabilities:
Balance at Beginning of Period	0.0	5.9
Losses (Gains) during Period		(1.4)
Adjustments		(4.1)
Additions		0.0
Settlements		(0.4)
Foreign Currency Translation		0.0
Balance at End of Period		0.0
Note receivable - building sale
Assets:
Balance at Beginning of Period	0.0	6.2	$ 0.0
(Losses) Gains during Period	0.8	(0.8)
Adjustments	0.0	0.0
Additions	0.0	7.0
Settlements	(7.0)	0.0
Foreign Currency Translation	$ 0.0	$ 0.0