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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, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Gain (Loss) on Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Other-than-temporary impairment (OTTI) losses gross |  |  |  |  |  |  |  |  | $ (46) | $ (111) | $ (151)
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Loss, before Tax, Including Portion Attributable to Noncontrolling Interest |  |  |  |  |  |  |  |  | 1 | 8 | 39
Foreign exchange gains( losses) |  |  |  |  |  |  |  |  | 36 | 118 | (80)
Fair Value adjustment on insurance derivative |  |  |  |  |  |  |  |  | 364 | 53 | (203)
Derivative, Gain (Loss) on Derivative, Net |  |  |  |  |  |  |  |  | 87 | (126) | (193)
Total Net realized gains (losses) including OTTI | $ 0 | $ (10) | $ 101 | $ (7) | $ 365 | $ 100 | $ (216) | $ (394) | 84 | (145) | (420)
Unrealized Gain (Loss) on Investments |  |  |  |  |  |  |  |  | 392 | 184 | (977)
Other Comprehensive Income (Loss), Available-for-sale Securities, Tax |  |  |  |  |  |  |  |  | (241) | 100 | 152
Total net realized gains (losses) and change in net unrealized appreciation (depreciation) on investments |  |  |  |  |  |  |  |  | 476 | 39 | (1,397)
Other derivative instruments |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Derivative, Gain (Loss) on Derivative, Net |  |  |  |  |  |  |  |  | (5) | (10) | (12)
Investment and embedded derivative instruments |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Derivative, Gain (Loss) on Derivative, Net |  |  |  |  |  |  |  |  | (11) | (33) | 32
S&P Options and Futures |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Derivative, Gain (Loss) on Derivative, Net |  |  |  |  |  |  |  |  | (261) | (136) | (10)
Equity Securities [Member] |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Cost-method Investments, Other than Temporary Impairment |  |  |  |  |  |  |  |  | (10) | (8) | (7)
Equity Securities - Gross Realized Gains Excluding OTTI |  |  |  |  |  |  |  |  | 28 | 65 | 47
Equity Securities - Gross realized losses excluding OTTI |  |  |  |  |  |  |  |  | (2) | (13) | (11)
Total Equity Securities |  |  |  |  |  |  |  |  | 16 | 44 | 29
Unrealized Gain (Loss) on Investments |  |  |  |  |  |  |  |  | 88 | 52 | (17)
Fixed maturities held to maturity |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unrealized Gain (Loss) on Investments |  |  |  |  |  |  |  |  | 18 | (59) | 43
Other Investments [Member] |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Cost-method Investments, Other than Temporary Impairment |  |  |  |  |  |  |  |  | (12) | (14) | (2)
Gain (Loss) on Sale of Other Investments |  |  |  |  |  |  |  |  | (12) | (4) | 6
Unrealized Gain (Loss) on Investments |  |  |  |  |  |  |  |  | 8 | (51) | (36)
Available-for-sale Securities [Member] |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unrealized Gain (Loss) on Investments |  |  |  |  |  |  |  |  | 519 | 142 | (1,119)
Debt Securities [Member] |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Other-than-temporary impairment (OTTI) losses gross |  |  |  |  |  |  |  |  | (24) | (89) | (142)
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Loss, before Tax, Including Portion Attributable to Noncontrolling Interest |  |  |  |  |  |  |  |  | 1 | 8 | 39
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities |  |  |  |  |  |  |  |  | (23) | (81) | (103)
Available-for-sale Securities, Gross Realized Gains |  |  |  |  |  |  |  |  | 149 | 183 | 158
Available-for-sale Securities, Gross Realized Losses |  |  |  |  |  |  |  |  | (157) | (265) | (235)
Available-for-sale Securities, Gross Realized Gain (Loss) |  |  |  |  |  |  |  |  | $ (31) | $ (163) | $ (180)

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