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Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Gross Derivative Assets and Liabilities by Type and Balance Sheet Location (Details) position in Millions, $ in Millions | Sep. 30, 2020 USD ($) position | Sep. 30, 2019 USD ($) position
--- | --- | ---
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | $ 3,264.4 | $ 3,671.5
Derivative liability, fair value, gross liability | 3,069.5 | 3,604.5
Gross fair value of derivative contracts | (3,319.0) | (3,581.9)
Gross fair value of derivative contracts | $ (3,100.7) | $ (3,540.8)
Derivative, number of instruments held | position | 7.9 | 10.6
Deposits and Receivables from Exchange Clearing Organizations [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivative, fair value, net | $ (173.5) | $ 23.1
Receivable From Clients, Net [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivative, fair value, net | 1.5 | 0.0
Financial Instruments Owned [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivative, fair value, net | 117.4 | 66.5
Payables To Clients [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivative, fair value, net | (222.7) | 0.0
Payables to Broker-dealers, Clearing Organizations and Counterparties [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivative, fair value, net | 14.7 | 5.6
Financial Instrument Sold, Not Yet Purchased [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivative, fair value, net | 176.8 | 58.1
Exchange-traded Commodity Derivatives [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 1,637.2 | 1,437.1
Derivative liability, fair value, gross liability | 1,747.3 | 1,463.4
OTC Commodity Derivatives [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 553.9 | 84.2
Derivative liability, fair value, gross liability | 433.2 | 106.2
Exchange-traded Foreign Exchange Derivatives [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 9.3 | 36.9
Derivative liability, fair value, gross liability | 13.0 | 33.5
OTC Foreign Exchange Derivatives [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 520.8 | 403.2
Derivative liability, fair value, gross liability | 461.5 | 368.8
Exchange-traded interest rate contracts [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 271.1 | 900.1
Derivative liability, fair value, gross liability | 200.7 | 882.0
OTC Interest Rate Derivatives [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 96.0 | 42.1
Derivative liability, fair value, gross liability | 96.6 | 43.6
Exchange-traded Equity Index Derivatives [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 32.1 | 758.1
Derivative liability, fair value, gross liability | 39.8 | 700.2
OTC Equity And Indices Contract [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 113.0 | 0.0
Derivative liability, fair value, gross liability | 55.4 | 0.0
TBA and Forward Settling Securities [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 31.0 | 9.8
Derivative liability, fair value, gross liability | $ 22.0 | $ 6.8

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- Definition Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226000-175313 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 20 -Section 50 -Paragraph 4D -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=121570589&loc=SL51823488-111719 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4B -Subparagraph (a),(c) -URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5624163-113959 + Details
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