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Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Realized Gains/Losses on Derivative Contracts (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
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Mar. 31, 2019 | Mar. 31, 2018 | Mar. 31, 2019 | Mar. 31, 2018
Commodity Contract [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative Instruments, Gain (Loss) Recognized in Income, Net | $ 36.0 | $ 12.3 | $ 44.1 | $ 33.8
Foreign Exchange Forward [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative Instruments, Gain (Loss) Recognized in Income, Net | 1.8 | 2.5 | 3.7 | 4.8
Equity [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative Instruments, Gain (Loss) Recognized in Income, Net | 0.7 | 0.0 | (2.6) | 0.0
Interest Rate Contract [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative Instruments, Gain (Loss) Recognized in Income, Net | 0.0 | 0.2 | 0.0 | 0.6
TBA and forward settling securities [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative Instruments, Gain (Loss) Recognized in Income, Net | 10.6 | 10.7 | 1.3 | 10.3
Derivative [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative Instruments, Gain (Loss) Recognized in Income, Net | $ 49.1 | $ 25.7 | $ 46.5 | $ 49.5

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- Definition Amount of increase (decrease) in the fair value of derivatives recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5618551-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (a),(c),(d),(e) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959 + 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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