EMPLOYEE BENEFITS (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Defined Contribution Plan
Company contribution amount		$ 0.5	$ 0.3	$ 0.7
SMART Plan
Defined Contribution Plan
Company contribution amount	$ 2.1	$ 2.7	$ 4.0	$ 5.3
Cboe Europe Equities Employee Selected Stakeholder Contribution Plan
Defined Contribution Plan
Company contribution amount	$ 0.1