FAIR VALUE MEASUREMENT - Fair value hierarchy of financial instruments held (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Assets:
U.S. Treasury securities	$ 0.5	$ 20.8
Deferred compensation plan assets	38.9	36.7
Note receivable - building sale	6.4
Digital assets - safeguarded assets	0.0	51.3
Digital assets held		0.1
Total assets	45.8	108.9
Liabilities:
Contingent consideration liabilities		11.8
Deferred compensation plan liabilities	38.9	36.7
Digital assets - safeguarded liabilities	0.0	51.3
Cboe Digital restricted common units liability		18.7
Cboe Digital warrant liability		5.9
Debt	1,346.6	1,305.7
Total liabilities	1,385.5	1,430.1
Level 1
Assets:
U.S. Treasury securities	0.5	20.8
Deferred compensation plan assets	38.9	36.7
Note receivable - building sale	0.0
Digital assets - safeguarded assets		0.0
Digital assets held		0.1
Total assets	39.4	57.6
Liabilities:
Contingent consideration liabilities		0.0
Deferred compensation plan liabilities	38.9	36.7
Digital assets - safeguarded liabilities		0.0
Cboe Digital restricted common units liability		0.0
Cboe Digital warrant liability		0.0
Debt	0.0	0.0
Total liabilities	38.9	36.7
Level 2
Assets:
U.S. Treasury securities	0.0	0.0
Deferred compensation plan assets	0.0	0.0
Note receivable - building sale	0.0
Digital assets - safeguarded assets		51.3
Digital assets held		0.0
Total assets	0.0	51.3
Liabilities:
Contingent consideration liabilities		0.0
Deferred compensation plan liabilities	0.0	0.0
Digital assets - safeguarded liabilities		51.3
Cboe Digital restricted common units liability		0.0
Cboe Digital warrant liability		0.0
Debt	1,346.6	1,305.7
Total liabilities	1,346.6	1,357.0
Level 3
Assets:
U.S. Treasury securities	0.0	0.0
Deferred compensation plan assets	0.0	0.0
Note receivable - building sale	6.4
Digital assets - safeguarded assets		0.0
Digital assets held		0.0
Total assets	6.4	0.0
Liabilities:
Contingent consideration liabilities		11.8
Deferred compensation plan liabilities	0.0	0.0
Digital assets - safeguarded liabilities		0.0
Cboe Digital restricted common units liability		18.7
Cboe Digital warrant liability		5.9
Debt	0.0	0.0
Total liabilities	$ 0.0	$ 36.4