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Investments (Narrative) (Detail) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 USD ($) Security | Dec. 31, 2022 USD ($) Security | Dec. 31, 2021 USD ($)
Schedule Of Investments [Line Items] |  |  |
Fair value of securities on deposit with various regulatory authorities | $ 11 | $ 10 |
Number of securities in unrealized loss position for a continuous 12 month period | Security | 450 | 210 |
Rate that a security's fair value is below book value | 5.00% | 5.00% |
Increase decrease in other net realized (gains) losses | $ 30 | $ (7) | $ 21
Asset Pledged as Collateral [Member] |  |  |
Schedule Of Investments [Line Items] |  |  |
Fair value of securities pledged as collateral | $ 241 | $ 251 |
Securities In Unrealized Loss Position [Member] |  |  |
Schedule Of Investments [Line Items] |  |  |
Weighted average contractual maturity period in years for securities in an unrealized loss position | 14 years | 14 years |
Increase decrease in other net realized (gains) losses | $ 8 | $ 21 |
Fair Value Below Book Value Greater Than Five Percent [Member] |  |  |
Schedule Of Investments [Line Items] |  |  |
Number of securities in unrealized loss position for a continuous 12 month period | Security | 365 | 190 |

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