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Investments - Holding gains (losses) on equity securities still held (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Holding Gains (Losses) on Equity Securities Still Held [Line Items] |  |  |  |
Holding gains (losses) on equity securities still held | $ (9) | $ 16 | $ 123 | $ (176)
Realized gains (losses) on securities |  |  |  |
Holding Gains (Losses) on Equity Securities Still Held [Line Items] |  |  |  |
Holding gains (losses) on equity securities still held | (16) | 17 | 82 | (174)
Investment income |  |  |  |
Holding Gains (Losses) on Equity Securities Still Held [Line Items] |  |  |  |
Holding gains (losses) on equity securities still held | $ 7 | $ (1) | $ 41 | $ (2)

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- Definition holding gains (losses) on equity securities still held + References No definition available. + Details
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- Definition Amount of unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(3)(d)) -URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 321 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=123583765&loc=SL75117546-209714 + Details
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