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Investments (Schedule Of Amortized Cost And Fair Value Of HTM Fixed Maturities And Related OTTI Recognized In Accumulated Other Comprehensive Income) (Detail) - USD ($) $ in Millions | Sep. 30, 2021 | Jun. 30, 2021 | Dec. 31, 2020 | Sep. 30, 2020 | Jun. 30, 2020 | Dec. 31, 2019
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Schedule of Held-to-maturity Securities [Line Items] |  |  |  |  |  |
Debt Securities, Held-to-maturity | $ 10,550 |  | $ 11,697 |  |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss | (35) | $ (37) | (44) | $ (45) | $ (51) | $ 0
Debt securities, held to maturity, net carrying value | 10,515 |  | 11,653 |  |  |
Held-to-maturity, Gross Unrealized Appreciation | 605 |  | 859 |  |  |
Held-to-maturity, Gross Unrealized Depreciation | (1) |  | (2) |  |  |
Held to maturity, at Fair Value | 11,119 |  | 12,510 |  |  |
U.S. Treasury / Agency |  |  |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |  |  |
Debt Securities, Held-to-maturity | 1,209 |  | 1,392 |  |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss | 0 |  | 0 |  |  |
Debt securities, held to maturity, net carrying value | 1,209 |  | 1,392 |  |  |
Held-to-maturity, Gross Unrealized Appreciation | 38 |  | 60 |  |  |
Held-to-maturity, Gross Unrealized Depreciation | 0 |  | 0 |  |  |
Held to maturity, at Fair Value | 1,247 |  | 1,452 |  |  |
Non-U.S. |  |  |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |  |  |
Debt Securities, Held-to-maturity | 1,259 |  | 1,295 |  |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss | (5) |  | (7) |  |  |
Debt securities, held to maturity, net carrying value | 1,254 |  | 1,288 |  |  |
Held-to-maturity, Gross Unrealized Appreciation | 76 |  | 118 |  |  |
Held-to-maturity, Gross Unrealized Depreciation | 0 |  | (1) |  |  |
Held to maturity, at Fair Value | 1,330 |  | 1,405 |  |  |
Corporate and asset-backed securities |  |  |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |  |  |
Debt Securities, Held-to-maturity | 2,079 |  | 2,185 |  |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss | (28) |  | (35) |  |  |
Debt securities, held to maturity, net carrying value | 2,051 |  | 2,150 |  |  |
Held-to-maturity, Gross Unrealized Appreciation | 209 |  | 288 |  |  |
Held-to-maturity, Gross Unrealized Depreciation | 0 |  | 0 |  |  |
Held to maturity, at Fair Value | 2,260 |  | 2,438 |  |  |
Mortgage-backed securities |  |  |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |  |  |
Debt Securities, Held-to-maturity | 1,771 |  | 2,000 |  |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss | (1) |  | (1) |  |  |
Debt securities, held to maturity, net carrying value | 1,770 |  | 1,999 |  |  |
Held-to-maturity, Gross Unrealized Appreciation | 99 |  | 148 |  |  |
Held-to-maturity, Gross Unrealized Depreciation | (1) |  | (1) |  |  |
Held to maturity, at Fair Value | 1,868 |  | 2,146 |  |  |
Municipal |  |  |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |  |  |
Debt Securities, Held-to-maturity | 4,232 |  | 4,825 |  |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss | (1) |  | (1) |  |  |
Debt securities, held to maturity, net carrying value | 4,231 |  | 4,824 |  |  |
Held-to-maturity, Gross Unrealized Appreciation | 183 |  | 245 |  |  |
Held-to-maturity, Gross Unrealized Depreciation | 0 |  | 0 |  |  |
Held to maturity, at Fair Value | $ 4,414 |  | $ 5,069 |  |  |

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