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Investments Investments - Rollforward of credit loss allowance for bank loans (Details) - Bank loans, net - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2020 | Sep. 30, 2020
Debt and Equity Securities, FV-NI [Line Items] |  |
Beginning balance | $ (76) | $ 0
Net decreases (increases) related to credit losses | 10 | (20)
Reduction of allowance related to sales | 5 | 7
Write-offs | 0 | 5
Ending balance | $ (61) | (61)
Cumulative effect of change in accounting principle |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Beginning balance |  | $ (53)

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- Definition Amount, after recovery, of writeoff of financing receivable, charged against allowance for credit loss. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922352-210448 + Details
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