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Investments - Realized capital gains and losses by transaction type (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2020 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Investments [Abstract] |  |  |  |
Sales |  | $ 1,017 | $ 575 | $ (215)
Credit losses |  | (80) | (47) | (14)
Valuation of equity investments |  | 366 | 1,372 | (691)
Valuation and settlements of derivative instruments |  | 53 | (15) | 43
Realized capital gains (losses) | $ 4 | 1,356 | 1,885 | (877)
Fixed income and equity securities |  |  |  |
Schedule of Available for Sale Securities |  |  |  |
Gross realized gains |  | 1,209 | 607 | 120
Gross realized losses |  | $ (221) | $ (132) | $ (347)

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- Definition Amount of realized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27357-111563 + Details
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