REVENUE RECOGNITION - Revenue by Product Line and Segment (Details) $ in Millions	3 Months Ended
	Mar. 31, 2026 USD ($) segment fee	Mar. 31, 2025 USD ($)
Segment Reporting Information
Number of reportable segments | segment	5
Number of types of regulatory fees recognized | fee	2
Revenues	$ 1,272.8	$ 1,195.0
Services transferred at a point in time
Segment Reporting Information
Revenues	1,067.8	1,019.4
Services transferred over time
Segment Reporting Information
Revenues	205.0	175.6
Options
Segment Reporting Information
Revenues	668.4	584.6
Options | Services transferred at a point in time
Segment Reporting Information
Revenues	570.9	507.0
Options | Services transferred over time
Segment Reporting Information
Revenues	97.5	77.6
North American Equities
Segment Reporting Information
Revenues	415.7	460.1
North American Equities | Services transferred at a point in time
Segment Reporting Information
Revenues	344.3	394.6
North American Equities | Services transferred over time
Segment Reporting Information
Revenues	71.4	65.5
Europe and Asia Pacific
Segment Reporting Information
Revenues	119.4	93.1
Europe and Asia Pacific | Services transferred at a point in time
Segment Reporting Information
Revenues	95.5	71.9
Europe and Asia Pacific | Services transferred over time
Segment Reporting Information
Revenues	23.9	21.2
Futures
Segment Reporting Information
Revenues	38.9	35.3
Futures | Services transferred at a point in time
Segment Reporting Information
Revenues	30.3	27.2
Futures | Services transferred over time
Segment Reporting Information
Revenues	8.6	8.1
Global FX
Segment Reporting Information
Revenues	30.4	21.9
Global FX | Services transferred at a point in time
Segment Reporting Information
Revenues	26.8	18.7
Global FX | Services transferred over time
Segment Reporting Information
Revenues	3.6	3.2
Transaction and clearing fees
Segment Reporting Information
Revenues	1,026.4	832.6
Transaction and clearing fees | Options
Segment Reporting Information
Revenues	559.2	464.5
Transaction and clearing fees | North American Equities
Segment Reporting Information
Revenues	342.0	271.7
Transaction and clearing fees | Europe and Asia Pacific
Segment Reporting Information
Revenues	68.6	50.8
Transaction and clearing fees | Futures
Segment Reporting Information
Revenues	30.3	27.1
Transaction and clearing fees | Global FX
Segment Reporting Information
Revenues	26.3	18.5
Access and capacity fees
Segment Reporting Information
Revenues	113.2	97.8
Access and capacity fees | Options
Segment Reporting Information
Revenues	53.4	44.0
Access and capacity fees | North American Equities
Segment Reporting Information
Revenues	38.7	34.5
Access and capacity fees | Europe and Asia Pacific
Segment Reporting Information
Revenues	12.1	10.9
Access and capacity fees | Futures
Segment Reporting Information
Revenues	5.8	5.6
Access and capacity fees | Global FX
Segment Reporting Information
Revenues	3.2	2.8
Market data fees
Segment Reporting Information
Revenues	91.8	77.8
Market data fees | Options
Segment Reporting Information
Revenues	44.1	33.6
Market data fees | North American Equities
Segment Reporting Information
Revenues	32.7	31.0
Market data fees | Europe and Asia Pacific
Segment Reporting Information
Revenues	11.8	10.3
Market data fees | Futures
Segment Reporting Information
Revenues	2.8	2.5
Market data fees | Global FX
Segment Reporting Information
Revenues	0.4	0.4
Regulatory fees
Segment Reporting Information
Revenues	10.4	161.8
Regulatory fees | Options
Segment Reporting Information
Revenues	10.1	41.1
Regulatory fees | North American Equities
Segment Reporting Information
Revenues	0.3	120.7
Regulatory fees | Europe and Asia Pacific
Segment Reporting Information
Revenues	0.0	0.0
Regulatory fees | Futures
Segment Reporting Information
Revenues	0.0	0.0
Regulatory fees | Global FX
Segment Reporting Information
Revenues	0.0	0.0
Other revenue
Segment Reporting Information
Revenues	31.0	25.0
Other revenue | Options
Segment Reporting Information
Revenues	1.6	1.4
Other revenue | North American Equities
Segment Reporting Information
Revenues	2.0	2.2
Other revenue | Europe and Asia Pacific
Segment Reporting Information
Revenues	26.9	21.1
Other revenue | Futures
Segment Reporting Information
Revenues	0.0	0.1
Other revenue | Global FX
Segment Reporting Information
Revenues	0.5	0.2
Cash and spot markets
Segment Reporting Information
Revenues	482.2	500.9
Cash and spot markets | Transaction and clearing fees
Segment Reporting Information
Revenues	436.9	341.0
Cash and spot markets | Access and capacity fees
Segment Reporting Information
Revenues	0.0	0.0
Cash and spot markets | Market data fees
Segment Reporting Information
Revenues	15.7	15.7
Cash and spot markets | Regulatory fees
Segment Reporting Information
Revenues	0.3	120.7
Cash and spot markets | Other revenue
Segment Reporting Information
Revenues	29.3	23.5
Data Vantage
Segment Reporting Information
Revenues	181.3	152.5
Data Vantage | Transaction and clearing fees
Segment Reporting Information
Revenues	0.0	0.0
Data Vantage | Access and capacity fees
Segment Reporting Information
Revenues	113.2	97.8
Data Vantage | Market data fees
Segment Reporting Information
Revenues	67.1	54.0
Data Vantage | Regulatory fees
Segment Reporting Information
Revenues	0.0	0.0
Data Vantage | Other revenue
Segment Reporting Information
Revenues	1.0	0.7
Derivatives markets
Segment Reporting Information
Revenues	609.3	541.6
Derivatives markets | Transaction and clearing fees
Segment Reporting Information
Revenues	589.5	491.6
Derivatives markets | Access and capacity fees
Segment Reporting Information
Revenues	0.0	0.0
Derivatives markets | Market data fees
Segment Reporting Information
Revenues	9.0	8.1
Derivatives markets | Regulatory fees
Segment Reporting Information
Revenues	10.1	41.1
Derivatives markets | Other revenue
Segment Reporting Information
Revenues	$ 0.7	$ 0.8