| Fair Value, Assets Measured on Recurring Basis [Table Text Block] |
The following tables set forth the Company’s financial and nonfinancial assets and liabilities accounted for at fair value, on a recurring basis, as of September 30, 2014 and September 30, 2013 by level in the fair value hierarchy. There were no assets or liabilities that were measured at fair value on a nonrecurring basis as of September 30, 2014 and 2013. | | | | | | | | | | | | | | | | | | | | | | September 30, 2014 | (in millions) | Level 1 | | Level 2 | | Level 3 | | Netting and
Collateral
(1) | | Total | Assets: | | | | | | | | | | Unrestricted cash equivalents - certificates of deposits | 1.5 |
| | — |
| | — |
| | — |
| | 1.5 |
| Commodities warehouse receipts | 14.8 |
| | — |
| | — |
| | — |
| | 14.8 |
| U.S. government obligations | — |
| | 0.5 |
| | — |
| | — |
| | 0.5 |
| Securities and other assets segregated under federal and other regulations | 14.8 |
| | 0.5 |
| | — |
| | — |
| | 15.3 |
| Money market funds | 826.8 |
| | — |
| | — |
| | — |
| | 826.8 |
| U.S. government obligations | — |
| | 702.5 |
| | — |
| | — |
| | 702.5 |
| Derivatives | 3,397.1 |
| | — |
| | — |
| | (3,671.0 | ) | | (273.9 | ) | Deposits and receivables from exchange-clearing organizations | 4,223.9 |
| | 702.5 |
| | — |
| | (3,671.0 | ) | | 1,255.4 |
| Deposits and receivables from broker-dealers, clearing organizations and counterparties - derivatives | 549.0 |
| | — |
| | — |
| | (550.1 | ) | | (1.1 | ) | Common and preferred stock and American Depositary Receipts (“ADRs”) | 66.8 |
| | 15.0 |
| | 0.7 |
| | — |
| | 82.5 |
| Exchangeable foreign ordinary equities and ADRs | 27.2 |
| | — |
| | — |
| | — |
| | 27.2 |
| Corporate and municipal bonds | 7.1 |
| | 9.0 |
| | 3.6 |
| | — |
| | 19.7 |
| U.S. government obligations | — |
| | 0.3 |
| | — |
| | — |
| | 0.3 |
| Foreign government obligations | — |
| | 10.7 |
| | — |
| | — |
| | 10.7 |
| Derivatives | 332.4 |
| | 2,328.3 |
| | — |
| | (2,616.4 | ) | | 44.3 |
| Commodities leases | — |
| | 60.1 |
| | — |
| | (58.0 | ) | | 2.1 |
| Commodities warehouse receipts | 3.6 |
| | — |
| | — |
| | — |
| | 3.6 |
| Exchange firm common stock | 4.8 |
| | — |
| | — |
| | — |
| | 4.8 |
| Mutual funds and other | 2.7 |
| | — |
| | — |
| | — |
| | 2.7 |
| Financial instruments owned | 444.6 |
| | 2,423.4 |
| | 4.3 |
| | (2,674.4 | ) | | 197.9 |
| Total assets at fair value | $ | 5,233.8 |
| | $ | 3,126.4 |
| | $ | 4.3 |
| | $ | (6,895.5 | ) | | $ | 1,469.0 |
| Liabilities: | | | | | | | | | | Accounts payable and other accrued liabilities - contingent liabilities | $ | — |
| | $ | — |
| | $ | 5.5 |
| | $ | — |
| | $ | 5.5 |
| Payable to customers - derivatives | 3,469.8 |
| | — |
| | — |
| | (3,469.8 | ) | | — |
| Common and preferred stock and ADRs | 92.8 |
| | 2.6 |
| | — |
| | — |
| | 95.4 |
| Exchangeable foreign ordinary equities and ADRs | 5.8 |
| | — |
| | — |
| | — |
| | 5.8 |
| Corporate and municipal bonds | 2.8 |
| | — |
| | — |
| | — |
| | 2.8 |
| Derivatives | 327.0 |
| | 2,257.7 |
| | — |
| | (2,500.3 | ) | | 84.4 |
| Commodities leases | — |
| | 176.0 |
| | — |
| | (100.4 | ) | | 75.6 |
| Financial instruments sold, not yet purchased | 428.4 |
| | 2,436.3 |
| | — |
| | (2,600.7 | ) | | 264.0 |
| Total liabilities at fair value | $ | 3,898.2 |
| | $ | 2,436.3 |
| | $ | 5.5 |
| | $ | (6,070.5 | ) | | $ | 269.5 |
|
| | (1) | Represents cash collateral and the impact of netting across the levels of the fair value hierarchy. Netting among positions classified within the same level are included in that level. |
| | | | | | | | | | | | | | | | | | | | | | September 30, 2013 | (in millions) | Level 1 | | Level 2 | | Level 3 | | Netting and
Collateral
(1) | | Total | Assets: | | | | | | | | | | Money market funds | $ | 0.1 |
| | $ | — |
| | $ | — |
| | $ | — |
| | $ | 0.1 |
| Certificate of deposits | 2.9 |
| | — |
| | — |
| | — |
| | 2.9 |
| Unrestricted cash equivalents | 3.0 |
| | — |
| | — |
| | — |
| | 3.0 |
| Money market funds | 75.0 |
| | — |
| | — |
| | — |
| | 75.0 |
| Commodities warehouse receipts | 13.1 |
| | — |
| | — |
| | — |
| | 13.1 |
| U.S. government obligations | — |
| | 19.5 |
| | — |
| | — |
| | 19.5 |
| Securities and other assets segregated under federal and other regulations | 88.1 |
| | 19.5 |
| | — |
| | — |
| | 107.6 |
| Money market funds | 841.4 |
| | — |
| | — |
| | — |
| | 841.4 |
| U.S. government obligations | — |
| | 594.8 |
| | — |
| | — |
| | 594.8 |
| Mortgage-backed securities | — |
| | 5.3 |
| | — |
| | — |
| | 5.3 |
| Derivatives | 2,263.2 |
| | — |
| | — |
| | (2,333.0 | ) | | (69.8 | ) | Deposits and receivables from exchange-clearing organizations | 3,104.6 |
| | 600.1 |
| | — |
| | (2,333.0 | ) | | 1,371.7 |
| Deposits and receivables from broker-dealers, clearing organizations and counterparties - derivatives | 1.8 |
| | 0.2 |
| | — |
| | (15.1 | ) | | (13.1 | ) | Common and preferred stock and American Depositary Receipts (“ADRs”) | 49.3 |
| | 19.8 |
| | 0.7 |
| | — |
| | 69.8 |
| Exchangeable foreign ordinary equities and ADRs | 36.7 |
| | — |
| | — |
| | — |
| | 36.7 |
| Corporate and municipal bonds | 0.1 |
| | — |
| | 3.5 |
| | — |
| | 3.6 |
| U.S. government obligations | — |
| | 0.3 |
| | — |
| | — |
| | 0.3 |
| Foreign government obligations | 7.7 |
| | — |
| | — |
| | — |
| | 7.7 |
| Derivatives | 173.6 |
| | 440.6 |
| | — |
| | (592.3 | ) | | 21.9 |
| Commodities leases | — |
| | 56.1 |
| | — |
| | (50.0 | ) | | 6.1 |
| Commodities warehouse receipts | 4.0 |
| | — |
| | — |
| | — |
| | 4.0 |
| Exchange firm common stock | 4.4 |
| | — |
| | — |
| | — |
| | 4.4 |
| Mutual funds and other | 4.0 |
| | — |
| | — |
| | — |
| | 4.0 |
| Financial instruments owned | 279.8 |
| | 516.8 |
| | 4.2 |
| | (642.3 | ) | | 158.5 |
| Total assets at fair value | $ | 3,477.3 |
| | $ | 1,136.6 |
| | $ | 4.2 |
| | $ | (2,990.4 | ) | | $ | 1,627.7 |
| Liabilities: | | | | | | | | | | Accounts payable and other accrued liabilities - contingent liabilities | $ | — |
| | $ | — |
| | $ | 9.6 |
| | $ | — |
| | $ | 9.6 |
| Payable to customers - derivatives | 2,328.2 |
| | — |
| | — |
| | (2,328.2 | ) | | — |
| Common and preferred stock and ADRs | 82.9 |
| | 16.6 |
| | — |
| | — |
| | 99.5 |
| Exchangeable foreign ordinary equities and ADRs | 8.7 |
| | — |
| | — |
| | — |
| | 8.7 |
| Derivatives | 174.0 |
| | 473.2 |
| | — |
| | (616.5 | ) | | 30.7 |
| Commodities leases | — |
| | 85.5 |
| | — |
| | (44.5 | ) | | 41.0 |
| Financial instruments sold, not yet purchased | 265.6 |
| | 575.3 |
| | — |
| | (661.0 | ) | | 179.9 |
| Total liabilities at fair value | $ | 2,593.8 |
| | $ | 575.3 |
| | $ | 9.6 |
| | $ | (2,989.2 | ) | | $ | 189.5 |
|
| | (1) | Represents cash collateral and the impact of netting across the levels of the fair value hierarchy. Netting among positions classified within the same level are included in that level. |
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] |
The Company’s financial assets at fair value classified within level 3 of the fair value hierarchy as of September 30, 2014 and 2013 are summarized below: | | | | | | | | | (in millions) | September 30, 2014 | | September 30, 2013 | Total level 3 assets | $ | 4.3 |
| | $ | 4.2 |
| Level 3 assets for which the Company bears economic exposure | $ | 4.3 |
| | $ | 4.2 |
| Total assets | $ | 3,039.7 |
| | $ | 2,848.0 |
| Total financial assets at fair value | $ | 1,469.0 |
| | $ | 1,627.7 |
| Total level 3 assets as a percentage of total assets | 0.1 | % | | 0.1 | % | Level 3 assets for which the Company bears economic exposure as a percentage of total assets | 0.1 | % | | 0.1 | % | Total level 3 assets as a percentage of total financial assets at fair value | 0.3 | % | | 0.3 | % |
The following tables set forth a summary of changes in the fair value of the Company’s level 3 financial assets and liabilities during the fiscal years ended September 30, 2014 and 2013, including a summary of unrealized gains (losses) during the fiscal year ended on the Company’s level 3 financial assets and liabilities still held as of September 30, 2014. | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Level 3 Financial Assets and Financial Liabilities
For the Year Ended September 30, 2014 | (in millions) | Balances at
beginning of
period | | Realized gains
(losses) during
period | | Unrealized
gains (losses)
during period | | Purchases/
issuances | | Settlements | | Transfers in
or (out) of
Level 3 | | Balances at
end of period | Assets: | | | | | | | | | | | | | | Common and preferred stock and ADRs | $ | 0.7 |
| | $ | — |
| | $ | — |
| | $ | — |
| | $ | — |
| | $ | — |
| | $ | 0.7 |
| Corporate and municipal bonds | 3.5 |
| | — |
| | 0.1 |
| | — |
| | — |
| | — |
| | 3.6 |
| | $ | 4.2 |
| | $ | — |
| | $ | 0.1 |
| | $ | — |
| | $ | — |
| | $ | — |
| | $ | 4.3 |
| | | | | | | | | | | | | | | (in millions) | Balances at
beginning of
period | | Realized gains
(losses) during
period | | Remeasurement
gains (losses)
during period | | Acquisitions | | Settlements | | Transfers in
or (out) of
Level 3 | | Balances at
end of period | Liabilities: | | | | | | | | | | | | | | Contingent liabilities | $ | 9.6 |
| | $ | — |
| | $ | (2.3 | ) | | $ | 0.5 |
| | $ | (2.3 | ) | | $ | — |
| | $ | 5.5 |
|
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Level 3 Financial Assets and Financial Liabilities
For the Year Ended September 30, 2013 | (in millions) | Balances at
beginning of
period | | Realized gains
(losses) during
period | | Unrealized
gains (losses)
during period | | Purchases/
issuances | | Settlements | | Transfers in
or (out) of
Level 3 | | Balances at
end of period | Assets: | | | | | | | | | | | | | | Common and preferred stock and ADRs | $ | 0.9 |
| | $ | — |
| | $ | (0.2 | ) | | $ | — |
| | $ | — |
| | $ | — |
| | $ | 0.7 |
| Corporate and municipal bonds | 3.6 |
| | — |
| | (0.1 | ) | | — |
| | — |
| | — |
| | 3.5 |
| | $ | 4.5 |
| | $ | — |
| | $ | (0.3 | ) | | $ | — |
| | $ | — |
| | $ | — |
| | $ | 4.2 |
| | | | | | | | | | | | | | | (in millions) | Balances at
beginning of
period | | Realized gains
(losses) during
period | | Remeasurement
gains (losses)
during period | | Acquisitions | | Settlements | | Transfers in
or (out) of
Level 3 | | Balances at
end of period | Liabilities: | | | | | | | | | | | | | | Contingent liabilities | $ | 14.8 |
| | $ | — |
| | $ | 2.6 |
| | $ | 5.6 |
| | $ | (13.4 | ) | | $ | — |
| | $ | 9.6 |
|
|
| Available-for-sale Securities [Table Text Block] |
The following tables summarize the amortized cost basis, the aggregate fair value and gross unrealized holding gains and losses of the Company’s investment securities classified as available-for-sale as of September 30, 2014 and September 30, 2013: | | | | | | | | | | | | | | | | | September 30, 2014 | Amounts included in deposits with and receivables from exchange-clearing organizations: | | Amortized Cost | | Unrealized Holding (1) | | Estimated Fair Value | (in millions) | Gains | | (Losses) | | U.S. government obligations | $ | 666.8 |
| | $ | — |
| | $ | — |
| | $ | 666.8 |
|
| | (1) | Unrealized gain/loss on U.S. government obligations as of September 30, 2014, is less than 0.1 million. |
| | | | | | | | | | | | | | | | | September 30, 2013 | Amounts included in deposits with and receivables from exchange-clearing organizations: | | Amortized Cost | | Unrealized Holding (1) | | Estimated Fair Value | (in millions) | Gains | | (Losses) | | U.S. government obligations | $ | 568.5 |
| | $ | — |
| | $ | — |
| | $ | 568.5 |
| Mortgage-backed securities | 5.2 |
| | 0.1 |
| | — |
| | 5.3 |
| | $ | 573.7 |
| | $ | 0.1 |
| | $ | — |
| | $ | 573.8 |
|
| | (1) | Unrealized gain/loss on U.S. government obligations as of September 30, 2013, is less than 0.1 million. |
As of September 30, 2014 and September 30, 2013, investments in debt securities classified as available-for-sale (AFS) mature as follows: | | | | | | | | | | | | | September 30, 2014 | | Due in | | Estimated Fair Value | (in millions) | Less than 1 year | | 1 year or more | | U.S. government obligations | $ | 287.6 |
| | $ | 379.2 |
| | $ | 666.8 |
|
| | | | | | | | | | | | | September 30, 2013 | | Due in | | Estimated Fair Value | (in millions) | Less than 1 year | | 1 year or more | | U.S. government obligations | $ | 568.5 |
| | $ | — |
| | $ | 568.5 |
| Mortgage-backed securities | — |
| | 5.3 |
| | 5.3 |
| | $ | 568.5 |
| | $ | 5.3 |
| | $ | 573.8 |
|
|