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Investments (Net Realized Gains (Losses) And Losses Included In Net Realized Gains (Losses) And Other Comprehensive Income) (Detail) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2021 | Mar. 31, 2020
Gain (Loss) on Securities [Line Items] |  |  |
Realized Investment Gains (Losses) |  | $ 887 | $ (958)
Foreign exchange gains |  | 76 | (68)
Fair Value, Option, Changes in Fair Value, Gain (Loss) |  | 319 | (685)
Gain (Loss) on Derivative |  | 383 | (547)
Other |  | (1) | 0
Fixed Maturities [Member] |  |  |
Gain (Loss) on Securities [Line Items] |  |  |
Debt Securities, Available-for-sale, Realized Gain, Excluding Other-than-temporary Impairment |  | 37 | 77
Debt Securities, Available-for-sale, Realized Loss, Excluding Other-than-temporary Impairment |  | (19) | (125)
Debt Securities, Allowance for Credit Loss, Period Increase (Decrease) |  | 6 | (150)
Debt Securities, Available-For-Sale, Credit Impairment Charges Intent to Sell | [1] | 0 | (121)
Debt Securities, Available-for-sale, Realized Gain (Loss) |  | 24 | (319)
Equity Securities [Member] |  |  |
Gain (Loss) on Securities [Line Items] |  |  |
Equity Securities, FV-NI, Realized Gain (Loss) |  | 367 | (29)
Other Investments [Member] |  |  |
Gain (Loss) on Securities [Line Items] |  |  |
Realized Investment Gains (Losses) |  | 38 | 5
Other derivative instruments |  |  |
Gain (Loss) on Securities [Line Items] |  |  |
Gain (Loss) on Derivative |  | (1) | (2)
Investment and embedded derivative instruments |  |  |
Gain (Loss) on Securities [Line Items] |  |  |
Gain (Loss) on Derivative |  | 109 | 15
S&P put options and futures |  |  |
Gain (Loss) on Securities [Line Items] |  |  |
Gain (Loss) on Derivative |  | (44) | 125
Accounting Standards Update 2016-13 [Member] |  |  |
Gain (Loss) on Securities [Line Items] |  |  |
Debt Securities, Allowance for Credit Loss, Period Increase (Decrease) |  | $ 4 | $ 149
[1] | Relates to certain securities we intended to sell and securities written to market entering default.

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