REVENUE RECOGNITION - Revenue by product line and Segment (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) segment item	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Segment Reporting Information
Number of types of regulatory fees the Company recognizes \| item	2
Revenues	$ 3,773.5	$ 3,958.5	$ 3,494.8
Number of reportable segments \| segment	6
Services transferred at a point in time
Segment Reporting Information
Revenues	$ 3,132.3	3,352.1	2,962.0
Services transferred over time
Segment Reporting Information
Revenues	641.2	606.4	532.8
Corporate Items and Eliminations
Segment Reporting Information
Revenues			0.3
Corporate Items and Eliminations \| Services transferred at a point in time
Segment Reporting Information
Revenues			0.3
Options \| Operating Segments
Segment Reporting Information
Revenues	1,939.5	1,823.2	1,505.0
Options \| Operating Segments \| Services transferred at a point in time
Segment Reporting Information
Revenues	1,659.7	1,562.8	1,296.7
Options \| Operating Segments \| Services transferred over time
Segment Reporting Information
Revenues	279.8	260.4	208.3
North American Equities \| Operating Segments
Segment Reporting Information
Revenues	1,353.0	1,681.7	1,570.5
North American Equities \| Operating Segments \| Services transferred at a point in time
Segment Reporting Information
Revenues	1,107.6	1,441.2	1,337.9
North American Equities \| Operating Segments \| Services transferred over time
Segment Reporting Information
Revenues	245.4	240.5	232.6
Europe and Asia Pacific \| Operating Segments
Segment Reporting Information
Revenues	281.2	264.6	240.3
Europe and Asia Pacific \| Operating Segments \| Services transferred at a point in time
Segment Reporting Information
Revenues	208.2	197.5	183.5
Europe and Asia Pacific \| Operating Segments \| Services transferred over time
Segment Reporting Information
Revenues	73.0	67.1	56.8
Futures \| Operating Segments
Segment Reporting Information
Revenues	129.0	119.8	120.6
Futures \| Operating Segments \| Services transferred at a point in time
Segment Reporting Information
Revenues	98.5	91.9	95.3
Futures \| Operating Segments \| Services transferred over time
Segment Reporting Information
Revenues	30.5	27.9	25.3
Global FX \| Operating Segments
Segment Reporting Information
Revenues	74.9	68.9	58.1
Global FX \| Operating Segments \| Services transferred at a point in time
Segment Reporting Information
Revenues	62.8	58.4	48.3
Global FX \| Operating Segments \| Services transferred over time
Segment Reporting Information
Revenues	12.1	10.5	9.8
Digital \| Operating Segments
Segment Reporting Information
Revenues	(4.1)	0.3
Digital \| Operating Segments \| Services transferred at a point in time
Segment Reporting Information
Revenues	(4.5)	0.3
Digital \| Operating Segments \| Services transferred over time
Segment Reporting Information
Revenues	0.4
Transaction and clearing fees
Segment Reporting Information
Revenues	2,831.3	2,938.8	2,693.1
Transaction and clearing fees \| Options \| Operating Segments
Segment Reporting Information
Revenues	1,583.7	1,471.7	1,231.2
Transaction and clearing fees \| North American Equities \| Operating Segments
Segment Reporting Information
Revenues	946.3	1,155.3	1,173.1
Transaction and clearing fees \| Europe and Asia Pacific \| Operating Segments
Segment Reporting Information
Revenues	145.6	161.9	145.3
Transaction and clearing fees \| Futures \| Operating Segments
Segment Reporting Information
Revenues	98.0	91.6	95.2
Transaction and clearing fees \| Global FX \| Operating Segments
Segment Reporting Information
Revenues	62.2	58.0	48.3
Transaction and clearing fees \| Digital \| Operating Segments
Segment Reporting Information
Revenues	(4.5)	0.3
Access and capacity fees
Segment Reporting Information
Revenues	347.5	324.2	280.7
Access and capacity fees \| Options \| Operating Segments
Segment Reporting Information
Revenues	161.0	151.7	124.0
Access and capacity fees \| North American Equities \| Operating Segments
Segment Reporting Information
Revenues	117.1	109.3	98.0
Access and capacity fees \| Europe and Asia Pacific \| Operating Segments
Segment Reporting Information
Revenues	36.3	34.0	31.2
Access and capacity fees \| Futures \| Operating Segments
Segment Reporting Information
Revenues	22.0	19.9	18.7
Access and capacity fees \| Global FX \| Operating Segments
Segment Reporting Information
Revenues	10.7	9.3	8.8
Access and capacity fees \| Digital \| Operating Segments
Segment Reporting Information
Revenues	0.4
Market data fees
Segment Reporting Information
Revenues	293.7	282.2	252.1
Market data fees \| Options \| Operating Segments
Segment Reporting Information
Revenues	118.8	108.7	84.3
Market data fees \| North American Equities \| Operating Segments
Segment Reporting Information
Revenues	128.3	131.2	134.6
Market data fees \| Europe and Asia Pacific \| Operating Segments
Segment Reporting Information
Revenues	36.7	33.1	25.6
Market data fees \| Futures \| Operating Segments
Segment Reporting Information
Revenues	8.5	8.0	6.6
Market data fees \| Global FX \| Operating Segments
Segment Reporting Information
Revenues	1.4	1.2	1.0
Regulatory fees
Segment Reporting Information
Revenues	223.7	364.7	208.3
Regulatory fees \| Options \| Operating Segments
Segment Reporting Information
Revenues	69.6	84.2	46.6
Regulatory fees \| North American Equities \| Operating Segments
Segment Reporting Information
Revenues	153.8	280.2	161.6
Regulatory fees \| Futures \| Operating Segments
Segment Reporting Information
Revenues	0.3	0.3	0.1
Other revenue
Segment Reporting Information
Revenues	77.3	48.6	60.6
Other revenue \| Corporate Items and Eliminations
Segment Reporting Information
Revenues			0.3
Other revenue \| Options \| Operating Segments
Segment Reporting Information
Revenues	6.4	6.9	18.9
Other revenue \| North American Equities \| Operating Segments
Segment Reporting Information
Revenues	7.5	5.7	3.2
Other revenue \| Europe and Asia Pacific \| Operating Segments
Segment Reporting Information
Revenues	62.6	35.6	38.2
Other revenue \| Futures \| Operating Segments
Segment Reporting Information
Revenues	0.2
Other revenue \| Global FX \| Operating Segments
Segment Reporting Information
Revenues	0.6	0.4
Cash and spot markets
Segment Reporting Information
Revenues	1,445.1	1,777.6	1,660.5
Cash and spot markets \| Transaction and clearing fees
Segment Reporting Information
Revenues	1,149.7	1,375.5	1,366.5
Cash and spot markets \| Market data fees
Segment Reporting Information
Revenues	71.3	80.3	91.6
Cash and spot markets \| Regulatory fees
Segment Reporting Information
Revenues	153.8	280.2	161.6
Cash and spot markets \| Other revenue
Segment Reporting Information
Revenues	70.3	41.6	40.8
Data and access solutions
Segment Reporting Information
Revenues	539.2	497.0	427.7
Data and access solutions \| Access and capacity fees
Segment Reporting Information
Revenues	347.5	324.2	280.7
Data and access solutions \| Market data fees
Segment Reporting Information
Revenues	188.7	168.7	130.0
Data and access solutions \| Other revenue
Segment Reporting Information
Revenues	3.0	4.1	17.0
Derivatives markets
Segment Reporting Information
Revenues	1,789.2	1,683.9	1,406.6
Derivatives markets \| Transaction and clearing fees
Segment Reporting Information
Revenues	1,681.6	1,563.3	1,326.6
Derivatives markets \| Market data fees
Segment Reporting Information
Revenues	33.7	33.2	30.5
Derivatives markets \| Regulatory fees
Segment Reporting Information
Revenues	69.9	84.5	46.7
Derivatives markets \| Other revenue
Segment Reporting Information
Revenues	$ 4.0	$ 2.9	$ 2.8