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Commitments, Contingencies and Guarantees (Narrative) (Details) - USD ($) |  | 3 Months Ended
--- | --- | ---
Aug. 10, 2020 | Mar. 31, 2021
Commitment And Contingencies [Line Items] |  |
Aggregate loss on securities |  | $ 44,000,000
Maximum aggregate loss, if securities' price falls to zero and no debts collected |  | 50,000,000
Guarantees, Fair Value Disclosure |  | $ 0
FINRA [Member] |  |
Commitment And Contingencies [Line Items] |  |
Settlement, penalties agreed to paid | $ 15,000,000 |
SEC [Member] |  |
Commitment And Contingencies [Line Items] |  |
Settlement, penalties agreed to paid | 11,500,000 |
CFTC [Member] |  |
Commitment And Contingencies [Line Items] |  |
Settlement, penalties agreed to paid | 11,500,000 |
Disgorgement [Member] |  |
Commitment And Contingencies [Line Items] |  |
Settlement, penalties agreed to paid | $ 700,000 |

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- Definition Commitment And Contingencies [Line Items] + References No definition available. + Details
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- Definition Maximum Aggregate Loss, If Securities' Price Falls To Zero And No Debts Collected + References No definition available. + Details
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- Definition Fair value portion of guarantee, including, but not limited to, financial standby letter of credit, fair value guarantee, guarantee of collection of scheduled contractual cash flows from financial assets, and contracts that contingently require the guarantor to make payments or perform services. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121555522&loc=d3e12201-110248 + Details
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- Definition Amount awarded to other party in judgment or settlement of litigation. + References No definition available. + Details
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- Definition Amount of unrealized and realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI). + References No definition available. + Details
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