CLEARING OPERATIONS - Valuation (Details) $ / shares in Units, $ in Millions	Dec. 31, 2023 USD ($) item $ / shares	Dec. 31, 2022 USD ($) item $ / shares	Jun. 30, 2022 USD ($)
Digital Assets - Safeguarded Assets and Safeguarded Liabilities
Fair Value	$ 51.3	$ 22.9	$ 22.4
Bitcoin
Digital Assets - Safeguarded Assets and Safeguarded Liabilities
Number of Units \| item	821	717
Valuation per Unit \| $ / shares	$ 42,492	$ 16,540
Fair Value	$ 34.9	$ 11.8
Ethereum
Digital Assets - Safeguarded Assets and Safeguarded Liabilities
Number of Units \| item	6,270	6,362
Valuation per Unit \| $ / shares	$ 2,282	$ 1,199
Fair Value	$ 14.3	$ 7.6
Litecoin
Digital Assets - Safeguarded Assets and Safeguarded Liabilities
Number of Units \| item	16,329	17,873
Valuation per Unit \| $ / shares	$ 74	$ 70
Fair Value	$ 1.2	$ 1.3
Bitcoin Cash
Digital Assets - Safeguarded Assets and Safeguarded Liabilities
Number of Units \| item	1,374	6,883
Valuation per Unit \| $ / shares	$ 261	$ 97
Fair Value	$ 0.4	$ 0.7
USD Coin
Digital Assets - Safeguarded Assets and Safeguarded Liabilities
Number of Units \| item	506,652	1,516,479
Valuation per Unit \| $ / shares	$ 1	$ 1
Fair Value	$ 0.5	$ 1.5