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Assets and Liabilities, at Fair Value - Financial Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Millions | Jun. 30, 2019 | Sep. 30, 2018
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and Securities Segregated under Federal and Other Regulations | $ 1,079.4 | $ 1,408.7
Financial Instruments, Owned, at Fair Value | 2,429.9 | 2,054.8
Physical commodities inventory | 347.8 | 222.5
Accounts Payable and Other Accrued Liabilities | 144.1 | 145.4
Payables to Broker-Dealers and Clearing Organizations | (190.7) | (89.5)
Financial Instruments Sold, Not yet Purchased, at Fair Value | 861.2 | 866.5
Fair Value, Measurements, Recurring [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and Securities Segregated under Federal and Other Regulations | 358.4 | 643.3
Receivables from Clearing Organizations | 380.4 | 517.4
Financial Instruments, Owned, at Fair Value | 2,429.9 | 2,054.8
Assets, Fair Value Disclosure | 3,345.1 | 3,376.2
Financial Instruments Sold, Not yet Purchased, at Fair Value | 861.2 |
Liabilities, Fair Value Disclosure | 875.2 | 866.5
Fair Value, Measurements, Recurring [Member] | TBA and forward settling securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payables to Broker-Dealers and Clearing Organizations | (7.9) | 0.0
Fair Value, Measurements, Recurring [Member] | Derivative [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payables to Broker-Dealers and Clearing Organizations | (6.1) | 0.0
Fair Value, Measurements, Recurring [Member] | Payable to broker-dealers, clearing organizations and counterparties [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payables to Broker-Dealers and Clearing Organizations | (14.0) | 0.0
Fair Value, Measurements, Recurring [Member] | Physical commodities inventory [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Physical commodities inventory | 169.9 | 156.9
Fair Value, Measurements, Recurring [Member] | Asset-backed Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 30.4 | 42.9
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 465.1 | 472.9
Financial Instruments Sold, Not yet Purchased, at Fair Value | 53.0 | 57.2
Fair Value, Measurements, Recurring [Member] | US Government Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 248.0 | 120.1
Financial Instruments Sold, Not yet Purchased, at Fair Value | 479.9 | 484.8
Fair Value, Measurements, Recurring [Member] | Debt Security, Government, Non-US [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 4.5 | 6.4
Financial Instruments Sold, Not yet Purchased, at Fair Value | 2.7 | 0.2
Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 1,148.7 | 1,022.5
Fair Value, Measurements, Recurring [Member] | Derivative [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 246.2 | 186.1
Fair Value, Measurements, Recurring [Member] | Commodities leases [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 26.8 | 17.7
Financial Instruments Sold, Not yet Purchased, at Fair Value | 45.6 | 59.3
Fair Value, Measurements, Recurring [Member] | Commodities warehouse receipts [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 39.6 | 16.4
Fair Value, Measurements, Recurring [Member] | Exchange firm common stock [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 11.7 | 10.2
Fair Value, Measurements, Recurring [Member] | Mutual funds and other [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 9.5 | 6.3
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 87.8 | 74.2
Financial Instruments Sold, Not yet Purchased, at Fair Value | 51.8 | 51.5
Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 111.6 | 79.1
Financial Instruments Sold, Not yet Purchased, at Fair Value | 29.2 | 20.1
Fair Value, Measurements, Recurring [Member] | US Government Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations | 484.2 |
Fair Value, Measurements, Recurring [Member] | Debt Security, Government, Non-US [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations | 10.5 | 7.7
Fair Value, Measurements, Recurring [Member] | TBA and forward settling securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations | 5.6 | 2.9
Fair Value, Measurements, Recurring [Member] | Derivative [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payables to Broker-Dealers and Clearing Organizations | (119.9) |
Fair Value, Measurements, Recurring [Member] | Commodities warehouse receipts [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and Securities Segregated under Federal and Other Regulations | 58.6 | 42.9
Fair Value, Measurements, Recurring [Member] | US Government Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and Securities Segregated under Federal and Other Regulations | 299.8 | 600.4
Fair Value, Measurements, Recurring [Member] | Certificates of Deposit [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and Cash Equivalents, Fair Value Disclosure | 6.5 | 3.8
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and Securities Segregated under Federal and Other Regulations | 0.0 | 0.0
Receivables from Clearing Organizations | (3,938.1) | (7,789.2)
Financial Instruments, Owned, at Fair Value | (355.0) | (341.1)
Assets, Fair Value Disclosure | (4,293.1) | (8,130.3)
Financial Instruments Sold, Not yet Purchased, at Fair Value | (496.1) | (510.8)
Liabilities, Fair Value Disclosure | (4,522.5) | (8,333.8)
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | TBA and forward settling securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payables to Broker-Dealers and Clearing Organizations | 0.5 | 2.1
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Derivative [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payables to Broker-Dealers and Clearing Organizations | 4,025.9 | 7,820.9
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Payable to broker-dealers, clearing organizations and counterparties [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payables to Broker-Dealers and Clearing Organizations | 4,026.4 | 7,823.0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Physical commodities inventory [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Physical commodities inventory | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Asset-backed Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | US Government Agencies Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | US Government Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Debt Security, Government, Non-US [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Collateralized Mortgage Backed Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Derivative [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | (343.7) | (329.3)
Financial Instruments Sold, Not yet Purchased, at Fair Value | (486.3) | (494.6)
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Commodities leases [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | (11.3) | (11.8)
Financial Instruments Sold, Not yet Purchased, at Fair Value | (9.8) | (16.2)
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Commodities warehouse receipts [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Exchange firm common stock [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Mutual funds and other [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Equity Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | US Government Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations | 0.0 |
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Debt Security, Government, Non-US [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations | 0.0 |
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | TBA and forward settling securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations | (0.5) |
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Derivative [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations | (3,937.6) |
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Commodities warehouse receipts [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and Securities Segregated under Federal and Other Regulations | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | US Government Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and Securities Segregated under Federal and Other Regulations | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Certificates of Deposit [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and Cash Equivalents, Fair Value Disclosure | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and Securities Segregated under Federal and Other Regulations | 358.4 | 643.3
Receivables from Clearing Organizations | 4,303.8 | 8,282.0
Financial Instruments, Owned, at Fair Value | 395.1 | 231.4
Assets, Fair Value Disclosure | 5,086.1 | 9,202.6
Financial Instruments Sold, Not yet Purchased, at Fair Value | 533.3 | 535.9
Liabilities, Fair Value Disclosure | 4,538.6 | 8,345.2
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | TBA and forward settling securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payables to Broker-Dealers and Clearing Organizations | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Derivative [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payables to Broker-Dealers and Clearing Organizations | (4,005.3) | (7,809.3)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Payable to broker-dealers, clearing organizations and counterparties [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payables to Broker-Dealers and Clearing Organizations | (4,005.3) | (7,809.3)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Physical commodities inventory [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Physical commodities inventory | 22.3 | 42.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Asset-backed Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Agencies Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 248.0 | 120.1
Financial Instruments Sold, Not yet Purchased, at Fair Value | 479.9 | 484.8
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Debt Security, Government, Non-US [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 4.5 | 6.4
Financial Instruments Sold, Not yet Purchased, at Fair Value | 2.7 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Collateralized Mortgage Backed Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Derivative [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 2.0 | 0.8
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commodities leases [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commodities warehouse receipts [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 39.6 | 16.4
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Exchange firm common stock [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 11.7 | 10.2
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Mutual funds and other [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 9.5 | 6.3
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 79.8 | 71.2
Financial Instruments Sold, Not yet Purchased, at Fair Value | 50.7 | 51.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations | 484.2 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Debt Security, Government, Non-US [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations | 10.5 | 7.7
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | TBA and forward settling securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Derivative [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations | 3,809.1 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commodities warehouse receipts [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and Securities Segregated under Federal and Other Regulations | 58.6 | 42.9
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and Securities Segregated under Federal and Other Regulations | 299.8 | 600.4
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Certificates of Deposit [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and Cash Equivalents, Fair Value Disclosure | 6.5 | 3.8
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and Securities Segregated under Federal and Other Regulations | 0.0 | 0.0
Receivables from Clearing Organizations | 14.7 | 24.6
Financial Instruments, Owned, at Fair Value | 2,389.8 | 2,164.5
Assets, Fair Value Disclosure | 2,552.1 | 2,303.9
Financial Instruments Sold, Not yet Purchased, at Fair Value | 824.0 | 841.4
Liabilities, Fair Value Disclosure | 859.1 | 855.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | TBA and forward settling securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payables to Broker-Dealers and Clearing Organizations | (8.4) | (2.1)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Derivative [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payables to Broker-Dealers and Clearing Organizations | (26.7) | (11.6)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Payable to broker-dealers, clearing organizations and counterparties [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payables to Broker-Dealers and Clearing Organizations | (35.1) | (13.7)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Physical commodities inventory [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Physical commodities inventory | 147.6 | 114.8
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Asset-backed Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 30.4 | 42.9
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Agencies Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 465.1 | 472.9
Financial Instruments Sold, Not yet Purchased, at Fair Value | 53.0 | 57.2
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Debt Security, Government, Non-US [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.2
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Collateralized Mortgage Backed Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 1,148.7 | 1,022.5
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Derivative [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 587.9 | 514.6
Financial Instruments Sold, Not yet Purchased, at Fair Value | 685.3 | 688.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commodities leases [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 38.1 | 29.5
Financial Instruments Sold, Not yet Purchased, at Fair Value | 55.4 | 75.5
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commodities warehouse receipts [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Exchange firm common stock [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Mutual funds and other [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 8.0 | 3.0
Financial Instruments Sold, Not yet Purchased, at Fair Value | 1.1 | 0.4
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 111.6 | 79.1
Financial Instruments Sold, Not yet Purchased, at Fair Value | 29.2 | 20.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations | 0.0 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Debt Security, Government, Non-US [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | TBA and forward settling securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations | 6.1 | 5.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Derivative [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations | 8.6 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commodities warehouse receipts [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and Securities Segregated under Federal and Other Regulations | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and Securities Segregated under Federal and Other Regulations | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Certificates of Deposit [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and Cash Equivalents, Fair Value Disclosure | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and Securities Segregated under Federal and Other Regulations | 0.0 | 0.0
Receivables from Clearing Organizations | 0.0 | 0.0
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Assets, Fair Value Disclosure | 0.0 | 0.0
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.0
Liabilities, Fair Value Disclosure | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | TBA and forward settling securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payables to Broker-Dealers and Clearing Organizations | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payables to Broker-Dealers and Clearing Organizations | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Payable to broker-dealers, clearing organizations and counterparties [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payables to Broker-Dealers and Clearing Organizations | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Physical commodities inventory [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Physical commodities inventory | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Asset-backed Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Agencies Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Debt Security, Government, Non-US [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Collateralized Mortgage Backed Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commodities leases [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commodities warehouse receipts [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Exchange firm common stock [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Mutual funds and other [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial Instruments, Owned, at Fair Value | 0.0 | 0.0
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations | 0.0 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Debt Security, Government, Non-US [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | TBA and forward settling securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations | 0.0 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commodities warehouse receipts [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and Securities Segregated under Federal and Other Regulations | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and Securities Segregated under Federal and Other Regulations | 0.0 | 0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Certificates of Deposit [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and Cash Equivalents, Fair Value Disclosure | $ 0.0 | 0.0
Collateralized Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations |  | (2.1)
Debt Security, Government, Non-US [Member] | Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations |  | 0.0
Derivative [Member] | Fair Value, Measurements, Recurring [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payables to Broker-Dealers and Clearing Organizations |  | (271.6)
Derivative [Member] | Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations |  | (7,787.1)
Derivative [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations |  | 7,495.9
Derivative [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations |  | 19.6
Derivative [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations |  | 0.0
US Government Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations |  | 778.4
US Government Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations |  | 0.0
US Government Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations |  | 778.4
US Government Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations |  | 0.0
US Government Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Receivables from Clearing Organizations |  | $ 0.0

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