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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 | 12 Months Ended
--- | --- | ---
Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Gain (Loss) on Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Other-than-temporary impairment (OTTI) losses gross |  |  |  |  |  |  |  |  |  | $ (90) | $ (52) | $ (46)
OTTI on Fixed Maturities |  |  |  |  |  |  |  |  |  | (58) | (49) | (45)
Foreign exchange gains( losses) |  |  |  |  |  |  |  |  |  | 7 | 131 | 36
Fair Value adjustment on insurance derivative |  |  |  |  |  |  |  |  |  | (4) | (248) | 364
Derivative, Gain (Loss) on Derivative, Net |  |  |  |  |  |  |  |  |  | (585) | (330) | 87
Net Realized Gains Losses |  | $ (55) | $ (155) | $ (223) | $ (97) | $ (687) | $ 19 | $ 18 | $ (2) | (530) | (652) | 84
Unrealized Gain (Loss) on Investments |  |  |  |  |  |  |  |  |  | 3,088 | (1,699) | 392
Other Comprehensive Income (Loss), Securities, Available-for-sale, Tax |  |  |  |  |  |  |  |  |  | (647) | 297 | (241)
Other derivative instruments |  |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Derivative, Gain (Loss) on Derivative, Net |  |  |  |  |  |  |  |  |  | (8) | (3) | (5)
Investment and embedded derivative instruments |  |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Derivative, Gain (Loss) on Derivative, Net |  |  |  |  |  |  |  |  |  | (435) | (75) | (11)
S&P Options and Futures |  |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Derivative, Gain (Loss) on Derivative, Net |  |  |  |  |  |  |  |  |  | (138) | (4) | (261)
Equity Securities [Member] |  |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Other-than-temporary impairment (OTTI) losses gross |  |  |  |  |  |  |  |  |  |  |  | (10)
Equity Securities - Gross Realized Gains Excluding OTTI |  |  |  |  |  |  |  |  |  |  |  | 28
Equity Securities - Gross realized losses excluding OTTI |  |  |  |  |  |  |  |  |  |  |  | (2)
Equity Securities, FV-NI, Realized Gain (Loss) |  |  |  |  |  |  |  |  |  | 104 | (59) |
Total net realized gains (losses) (includes $(302), $(15), and $(119) reclassified from AOCI) | [1] |  |  |  |  |  |  |  |  |  |  | 16
Unrealized Gain (Loss) on Investments |  |  |  |  |  |  |  |  |  | 0 | 0 | 88
Fixed maturities held to maturity |  |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Unrealized Gain (Loss) on Investments |  |  |  |  |  |  |  |  |  | (31) | (38) | 18
Other Investments [Member] |  |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Other-than-temporary impairment (OTTI) losses gross |  |  |  |  |  |  |  |  |  | 0 | 0 | (12)
Realized Investment Gains (Losses) |  |  |  |  |  |  |  |  |  | (20) | (5) | 0
Available-for-sale Securities [Member] |  |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Unrealized Gain (Loss) on Investments |  |  |  |  |  |  |  |  |  | 3,769 | (1,958) | 519
Debt Securities [Member] |  |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Other-than-temporary impairment (OTTI) losses gross |  |  |  |  |  |  |  |  |  | (90) | (52) | (24)
OTTI on fixed maturities recognized in OCI (pre-tax) |  |  |  |  |  |  |  |  |  | 32 | 3 | 1
OTTI on Fixed Maturities |  |  |  |  |  |  |  |  |  | (58) | (49) | (23)
Fixed Maturities [Member] |  |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Debt Securities, Available-for-sale, Realized Gain (Loss), Excluding Other-than-temporary Impairment |  |  |  |  |  |  |  |  |  | 203 | 334 | 149
Debt Securities, Available-for-sale, Realized Loss, Excluding Other-than-temporary Impairment |  |  |  |  |  |  |  |  |  | (176) | (587) | (157)
Debt Securities, Available-for-sale, Realized Gain (Loss) |  |  |  |  |  |  |  |  |  | (31) | (302) | (31)
Other [Member] |  |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Sale of Other Investments |  |  |  |  |  |  |  |  |  | (5) | (87) | (12)
Unrealized Gain (Loss) on Investments |  |  |  |  |  |  |  |  |  | (3) | 0 | $ 8
Accounting Standards Update 2016-01 [Member] | Equity Securities [Member] |  |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Equity Securities, FV-NI, Realized Gain (Loss) |  |  |  |  |  |  |  |  |  | 104 | (59) |
Unrealized Gain (Loss) on Investments |  |  |  |  |  |  |  |  |  | 46 | (129) |
Gain (Loss) on Sale of Investments |  |  |  |  |  |  |  |  |  | 58 | 70 |
Accounting Standards Update 2016-01 [Member] | Other Investments [Member] |  |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Realized Investment Gains (Losses) |  |  |  |  |  |  |  |  |  | (20) | (5) |
Unrealized Gain (Loss) on Investments |  |  |  |  |  |  |  |  |  | (15) | (126) |
Gain (Loss) on Sale of Investments |  |  |  |  |  |  |  |  |  | (5) | 121 |
Accounting Standards Update 2016-01 [Member] | Equity securities and other investments [Member] |  |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Realized Investment Gains (Losses) |  |  |  |  |  |  |  |  |  | 84 | (64) |
Unrealized Gain (Loss) on Investments |  |  |  |  |  |  |  |  |  | 31 | (255) |
Gain (Loss) on Sale of Investments |  |  |  |  |  |  |  |  |  | $ 53 | $ 191 |
[1] | 2017 included gross realized gains of $28 million and gross realized losses of $2 million on sales, and OTTI of $10 million.

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