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Assets and Liabilities, at Fair Value - Financial Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Millions | Dec. 31, 2017 | Sep. 30, 2017 | Sep. 30, 2015
--- | --- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Cash and Securities Segregated under Federal and Other Regulations | $ 464.4 | $ 518.8 |
Receivables from Brokers-Dealers and Clearing Organizations | 2,628.2 | 2,625.1 |
Financial Instruments, Owned, at Fair Value | 2,055.9 | 1,731.8 |
Physical commodities inventory | 244.7 | 124.8 |
Assets, Fair Value Disclosure | 2,273.5 | 2,068.0 |
Accounts Payable and Other Accrued Liabilities | 111.5 | 135.6 |
Payables to Broker-Dealers and Clearing Organizations | (197.1) | (125.7) |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 803.3 | 717.6 |
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 | 16.5 | 54.5 |
Receivables from Clearing Organizations | 53.7 | 204.7 |
Financial Instruments, Owned, at Fair Value | 2,055.9 | 1,731.8 |
Assets, Fair Value Disclosure | 2,273.5 | 2,068.0 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 803.3 |  |
Liabilities, Fair Value Disclosure | 804.4 | 723.4 |
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 | (1.1) | (4.8) |
Fair Value, Measurements, Recurring [Member] | Derivative [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Receivables from Brokers-Dealers and Clearing Organizations | 0.0 |  |
Payables to Broker-Dealers and Clearing Organizations |  | 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 | (1.1) | (4.8) |
Fair Value, Measurements, Recurring [Member] | Contingent Consideration [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Accounts Payable and Other Accrued Liabilities |  | 1.0 |
Fair Value, Measurements, Recurring [Member] | Physical commodities inventory - precious metals [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Physical commodities inventory | 142.7 | 73.2 |
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 | 21.6 | 47.3 |
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 | 587.7 | 368.9 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 35.5 | 27.9 |
Fair Value, Measurements, Recurring [Member] | Common stock and American Depositary Receipts (ADRs) [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial Instruments, Owned, at Fair Value | 34.0 | 34.7 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 49.8 | 34.4 |
Fair Value, Measurements, Recurring [Member] | Exchangeable foreign ordinary equities and ADRs [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial Instruments, Owned, at Fair Value | 10.1 | 10.4 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 10.2 | 10.5 |
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial Instruments, Owned, at Fair Value | 45.7 | 29.1 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.3 | 0.3 |
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 | 76.8 | 60.0 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 404.6 | 285.9 |
Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial Instruments, Owned, at Fair Value | 11.3 | 10.2 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 3.9 |  | $ 0.1
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 | 1,053.4 | 920.9 |
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 | 134.9 | 162.1 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 249.3 |  |
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 | 10.4 | 35.4 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 49.7 | 41.5 |
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 | 56.1 | 38.5 |
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 | 8.9 | 8.3 |
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 | 5.0 | 6.0 |
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 | 219.1 |  |
Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Receivables from Clearing Organizations | 6.2 | 6.4 |
Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Receivables from Clearing Organizations | 1.1 | 8.8 |
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 | (172.7) |  |
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 |  | 244.7 |
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 |  | (55.2) |
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 | 14.9 | 21.0 |
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 | 1.6 | 33.5 |
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 | 4.7 | 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 | (3,430.1) | (2,952.9) |
Financial Instruments, Owned, at Fair Value | (1,612.8) | (1,391.3) |
Assets, Fair Value Disclosure | (5,042.9) | (4,344.2) |
Financial Instruments Sold, Not yet Purchased, at Fair Value | (1,522.0) | (1,259.8) |
Liabilities, Fair Value Disclosure | (4,904.7) | (4,028.9) |
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 | 0.6 | 0.1 |
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 | 3,382.1 | 2,769.0 |
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 | 3,382.7 | 2,769.1 |
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Contingent Consideration [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Accounts Payable and Other Accrued Liabilities |  | 0.0 |
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Physical commodities inventory - precious metals [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 |  |
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] | Common stock and American Depositary Receipts (ADRs) [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] | Exchangeable foreign ordinary equities and ADRs [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] | Corporate 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] | Foreign 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] | 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 | (1,444.3) | (1,252.6) |
Financial Instruments Sold, Not yet Purchased, at Fair Value | (1,385.3) | (1,110.2) |
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 | (168.5) | (138.7) |
Financial Instruments Sold, Not yet Purchased, at Fair Value | (136.7) | (149.6) |
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] |  |  |
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] | 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] | Foreign 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] | Collateralized Mortgage Backed Securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Receivables from Clearing Organizations | (0.6) |  |
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 | (3,429.5) |  |
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Foreign 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] | Collateralized Mortgage Backed 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] | 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] | Derivative [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Receivables from Clearing Organizations |  | (2,952.9) |
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 | 16.5 | 54.5 |
Receivables from Clearing Organizations | 3,287.2 | 2,853.3 |
Financial Instruments, Owned, at Fair Value | 232.8 | 182.7 |
Assets, Fair Value Disclosure | 3,683.9 | 3,167.5 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 463.7 | 330.2 |
Liabilities, Fair Value Disclosure | 3,633.3 | 2,806.4 |
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 | (3,169.6) | (2,476.2) |
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 | (3,169.6) | (2,476.2) |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Contingent Consideration [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Accounts Payable and Other Accrued Liabilities |  | 0.0 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Physical commodities inventory - precious metals [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Physical commodities inventory | 142.7 | 73.2 |
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] | Common stock and American Depositary Receipts (ADRs) [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial Instruments, Owned, at Fair Value | 30.5 | 31.2 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 48.6 | 33.7 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Exchangeable foreign ordinary equities and ADRs [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial Instruments, Owned, at Fair Value | 9.0 | 9.2 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 10.2 | 10.3 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial Instruments, Owned, at Fair Value | 45.1 | 28.2 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.3 | 0.3 |
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 | 76.8 | 60.0 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 404.6 | 285.9 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign 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 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 | 1.4 | 1.3 |
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 | 56.1 | 38.5 |
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 | 8.9 | 8.3 |
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 | 5.0 | 6.0 |
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 | 219.1 |  |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign Government Debt 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] | Collateralized Mortgage Backed 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 | 3,068.1 |  |
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 |  | 244.7 |
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 |  | 2,608.6 |
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 | 14.9 | 21.0 |
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] |  |  |
Cash and Securities Segregated under Federal and Other Regulations | 1.6 | 33.5 |
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 | 4.7 | 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 | 196.6 | 304.3 |
Financial Instruments, Owned, at Fair Value | 3,435.8 | 2,940.3 |
Assets, Fair Value Disclosure | 3,632.4 | 3,244.6 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 1,861.6 | 1,647.2 |
Liabilities, Fair Value Disclosure | 2,075.8 | 1,944.9 |
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 | (1.7) | (4.9) |
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 | (212.5) | (292.8) |
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 | (214.2) | (297.7) |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Contingent Consideration [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Accounts Payable and Other Accrued Liabilities |  | 0.0 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Physical commodities inventory - precious metals [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 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 | 21.6 | 47.3 |
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 | 587.7 | 368.9 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 35.5 | 27.9 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Common stock and American Depositary Receipts (ADRs) [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial Instruments, Owned, at Fair Value | 3.4 | 3.4 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 1.2 | 0.7 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Exchangeable foreign ordinary equities and ADRs [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial Instruments, Owned, at Fair Value | 1.1 | 1.2 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.2 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial Instruments, Owned, at Fair Value | 0.6 | 0.9 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 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] |  |  |
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] | Foreign Government Debt Securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial Instruments, Owned, at Fair Value | 11.3 | 10.2 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 3.9 |  | 0.1
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 | 1,053.4 | 920.9 |
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 | 1,577.8 | 1,413.4 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 1,634.6 | 1,427.2 |
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 | 178.9 | 174.1 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 186.4 | 191.1 |
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] | 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] | Foreign Government Debt Securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Receivables from Clearing Organizations | 6.2 | 6.4 |
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] |  |  |
Receivables from Clearing Organizations | 1.7 | 8.8 |
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 | 188.7 |  |
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] | Derivative [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Receivables from Clearing Organizations |  | 289.1 |
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 | 0.1 | 0.1 |
Assets, Fair Value Disclosure | 0.1 | 0.1 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.0 |
Liabilities, Fair Value Disclosure | 0.0 | 1.0 |
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] | Contingent Consideration [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Accounts Payable and Other Accrued Liabilities |  | 1.0 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Physical commodities inventory - precious metals [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] | Common stock and American Depositary Receipts (ADRs) [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial Instruments, Owned, at Fair Value | 0.1 | 0.1 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.0 | 0.0 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Exchangeable foreign ordinary equities and ADRs [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] | Corporate 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] | Foreign 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] | 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] | 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] | Foreign Government Debt 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] | Collateralized Mortgage Backed 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] | 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] | 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 |

X
- Definition Amount of liabilities incurred and payable to vendors for goods and services received, and accrued liabilities classified as other. + References No definition available. + Details
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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References No definition available. + Details
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- Definition Amount of cash subject to withdrawal restrictions, restricted deposits held as compensating balances, and cash and securities segregated in compliance with regulations (such as cash deposited in a special reserve account for the exclusive benefit of customers). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 305 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6478312&loc=d3e61473-112792 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition The aggregate fair value as of the balance sheet date of financial instruments and other positions owned by the entity including: (1) mortgages, mortgage-backed and asset backed securities; (2) US government and agency obligations; (3) state and municipal government obligations; (4) other sovereign government debt; (5) corporate obligations; (6) corporate equities; (7) principal investments; (8) derivative contracts; and (9) physical commodities. Includes both pledged and unpledged holdings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 320 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=35711157&loc=d3e42546-110969 + Details
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- Definition Fair value of obligations incurred from short sales. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 320 -Section 35 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35711043&loc=d3e42429-110968 + Details
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- Definition Gross amount, as of the balance sheet date, of merchandise, goods, commodities, or supplies held for future sale or to be used in manufacturing, servicing or production process. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.6(a)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Fair value of financial and nonfinancial obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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