Assets and Liabilities, at Fair Value - Financial Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Millions | Sep. 30, 2015 | Sep. 30, 2014 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash and Securities Segregated under Federal and Other Regulations | $ 756.9 | $ 448 |
Receivables from Exchange Clearing Organizations | 1,533.5 | 1,731.4 |
Receivables from Brokers-Dealers and Clearing Organizations | 277.6 | 123 |
Financial instruments owned, at fair value | 1,421.9 | 197.9 |
Physical Commodities Inventory | 32.8 | 40 |
Assets, Fair Value Disclosure | 2,910.4 | 4.3 |
Accounts payable and other accrued liabilities | 144.8 | 114.1 |
Payables to Broker-Dealers and Clearing Organizations | 262.9 | 11.9 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 568.3 | 264 |
Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash and Cash Equivalents, Fair Value Disclosure | | 1.5 |
Cash and Securities Segregated under Federal and Other Regulations | 515.5 | 15.3 |
Receivables from Exchange Clearing Organizations | 1,009.4 | 1,255.4 |
Receivables from Brokers-Dealers and Clearing Organizations | (52.9) | |
Financial instruments owned, at fair value | 1,421.9 | 197.9 |
Assets, Fair Value Disclosure | 2,910.4 | 1,469 |
Payables to Broker-Dealers and Clearing Organizations | 1.6 | |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 568.3 | 264 |
Liabilities, Fair Value Disclosure | 573.2 | 269.5 |
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 | 1.6 | |
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 | 0 | |
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 | 3.3 | 5.5 |
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 | 15.2 | |
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 | 26.1 | 82.5 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 18.6 | 95.4 |
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 | 89.5 | 27.2 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 90 | 5.8 |
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 | 31.3 | 19.7 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 341 | 2.8 |
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 | 513.4 | 0.3 |
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 | 12.1 | 10.7 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 6.4 | |
Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Financial instruments owned, at fair value | 699.5 | |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 2.8 | |
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 | 30.6 | 44.3 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 54.1 | 84.4 |
Fair Value, Measurements, Recurring [Member] | Commodities leases and unpriced positions [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Financial instruments owned, at fair value | 7.6 | 2.1 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 55.4 | 75.6 |
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 | 2.8 | 3.6 |
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 | 5.6 | |
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 | 3.4 | 2.7 |
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 Brokers-Dealers and Clearing Organizations | 0.2 | |
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 | (53.1) | (1.1) |
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Receivables from Exchange Clearing Organizations | 431.8 | 826.8 |
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 Exchange Clearing Organizations | 501.4 | 702.5 |
Fair Value, Measurements, Recurring [Member] | Derivative [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Receivables from Exchange Clearing Organizations | 76.2 | (273.9) |
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 | 22.1 | 14.8 |
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 | 493.4 | 0.5 |
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 | 1.3 | |
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 Cash Equivalents, Fair Value Disclosure | | 1.5 |
Cash and Securities Segregated under Federal and Other Regulations | 22.1 | 14.8 |
Receivables from Exchange Clearing Organizations | 4,047.7 | 4,223.9 |
Receivables from Brokers-Dealers and Clearing Organizations | 0.1 | |
Financial instruments owned, at fair value | 423 | 444.6 |
Assets, Fair Value Disclosure | 4,509.4 | 5,233.8 |
Payables to Broker-Dealers and Clearing Organizations | 3,491.3 | |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 371 | 428.4 |
Liabilities, Fair Value Disclosure | 3,862.3 | 3,898.2 |
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 | |
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 | 3,491.3 | |
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 | 15.2 | |
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 | 23.7 | 66.8 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 18 | 92.8 |
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 | 82.9 | 27.2 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 89 | 5.8 |
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 | 26.1 | 7.1 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0 | 2.8 |
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 | 0 | 0 |
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 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0 | |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Mortgage Backed Securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Financial instruments owned, at fair value | 0 | |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 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 | 278.5 | 332.4 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 264 | 327 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commodities leases and unpriced positions [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Financial instruments owned, at fair value | 0 | 0 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 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 | 2.8 | 3.6 |
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 | 5.6 | 4.8 |
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 | 3.4 | 2.7 |
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 Brokers-Dealers and Clearing Organizations | 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 Brokers-Dealers and Clearing Organizations | 0.1 | 549 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Receivables from Exchange Clearing Organizations | 431.8 | 826.8 |
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 Exchange Clearing Organizations | 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 Exchange Clearing Organizations | 3,615.9 | 3,397.1 |
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 | 22.1 | 14.8 |
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 | 0 | 0 |
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 | 1.3 | |
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 Cash Equivalents, Fair Value Disclosure | | 0 |
Cash and Securities Segregated under Federal and Other Regulations | 493.4 | 0.5 |
Receivables from Exchange Clearing Organizations | 501.4 | 702.5 |
Receivables from Brokers-Dealers and Clearing Organizations | 539.1 | |
Financial instruments owned, at fair value | 3,002.1 | 2,423.4 |
Assets, Fair Value Disclosure | 4,536 | 3,126.4 |
Payables to Broker-Dealers and Clearing Organizations | 531.3 | |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 2,174.4 | 2,436.3 |
Liabilities, Fair Value Disclosure | 2,705.7 | 2,436.3 |
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 | 2.6 | |
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 | 528.7 | |
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 | |
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 | 1.9 | 15 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0.6 | 2.6 |
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 | 6.6 | 0 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 1 | 0 |
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 | 2 | 9 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 341 | 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 | 513.4 | 0.3 |
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 | 12.1 | 10.7 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 6.4 | |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Mortgage Backed Securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Financial instruments owned, at fair value | 699.5 | |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 2.8 | |
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] | | |
Financial instruments owned, at fair value | 1,702 | 2,328.3 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 1,723.5 | 2,257.7 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commodities leases and unpriced positions [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Financial instruments owned, at fair value | 64.6 | 60.1 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 99.1 | 176 |
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 |
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 |
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 |
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 Brokers-Dealers and Clearing Organizations | 1.2 | |
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 Brokers-Dealers and Clearing Organizations | 537.9 | 0 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Receivables from Exchange Clearing Organizations | 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 Exchange Clearing Organizations | 501.4 | 702.5 |
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] | | |
Receivables from Exchange Clearing Organizations | 0 | 0 |
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 |
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 | 493.4 | 0.5 |
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 | |
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 Cash Equivalents, Fair Value Disclosure | | 0 |
Cash and Securities Segregated under Federal and Other Regulations | 0 | 0 |
Receivables from Exchange Clearing Organizations | 0 | 0 |
Receivables from Brokers-Dealers and Clearing Organizations | 0 | |
Financial instruments owned, at fair value | 3.7 | 4.3 |
Assets, Fair Value Disclosure | 3.7 | 4.3 |
Payables to Broker-Dealers and Clearing Organizations | 0 | |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0 | 0 |
Liabilities, Fair Value Disclosure | 3.3 | 5.5 |
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 | |
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 | |
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 | 3.3 | 5.5 |
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 | |
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 | 0.5 | 0.7 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 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 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 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 | 3.2 | 3.6 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 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 |
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 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0 | |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Mortgage Backed Securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Financial instruments owned, at fair value | 0 | |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 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 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commodities leases and unpriced positions [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Financial instruments owned, at fair value | 0 | 0 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 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 |
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 |
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 |
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 Brokers-Dealers and Clearing Organizations | 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 Brokers-Dealers and Clearing Organizations | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Money Market Funds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Receivables from Exchange 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 Exchange 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 Exchange 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 |
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 |
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 | |
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 | | 0 |
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] | | |
Payables to Broker-Dealers and Clearing Organizations | | 3,469.8 |
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] | | |
Payables to Broker-Dealers and Clearing Organizations | | 0 |
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] | | |
Payables to Broker-Dealers and Clearing Organizations | | 0 |
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash and Cash Equivalents, Fair Value Disclosure | | 0 |
Cash and Securities Segregated under Federal and Other Regulations | 0 | 0 |
Receivables from Exchange Clearing Organizations | (3,539.7) | (3,671) |
Receivables from Brokers-Dealers and Clearing Organizations | (592.1) | |
Financial instruments owned, at fair value | (2,006.9) | (2,674.4) |
Assets, Fair Value Disclosure | (6,138.7) | (6,895.5) |
Payables to Broker-Dealers and Clearing Organizations | (4,021) | |
Financial Instruments Sold, Not yet Purchased, at Fair Value | (1,977.1) | (2,600.7) |
Liabilities, Fair Value Disclosure | (5,998.1) | (6,070.5) |
Counterparty And Cash Collateral Netting Adjustment [Member] | 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) | |
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 | (4,020) | |
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 | 0 | 0 |
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 | 0 | |
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 | 0 | 0 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0 | 0 |
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 | 0 | 0 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0 | 0 |
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 | 0 | 0 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0 | 0 |
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 | 0 | 0 |
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 | 0 | 0 |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0 | |
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Financial instruments owned, at fair value | 0 | |
Financial Instruments Sold, Not yet Purchased, at Fair Value | 0 | |
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 | (1,949.9) | (2,616.4) |
Financial Instruments Sold, Not yet Purchased, at Fair Value | (1,933.4) | (2,500.3) |
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Commodities leases and unpriced positions [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Financial instruments owned, at fair value | (57) | (58) |
Financial Instruments Sold, Not yet Purchased, at Fair Value | (43.7) | (100.4) |
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 | 0 | 0 |
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 | 0 | 0 |
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 | 0 | 0 |
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 Brokers-Dealers and Clearing Organizations | (1) | |
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 | (591.1) | (550.1) |
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Receivables from Exchange Clearing Organizations | 0 | 0 |
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 Exchange Clearing Organizations | 0 | 0 |
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Derivative [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Receivables from Exchange Clearing Organizations | (3,539.7) | (3,671) |
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 | 0 | 0 |
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 | 0 | 0 |
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 | $ 0 | |
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 | | $ (3,469.8) |