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v3.24.1.u1

Investments (Narrative) (Detail) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2024 USD ($) Security | Mar. 31, 2023 USD ($) | Dec. 31, 2023 USD ($) Security
Schedule Of Investments [Line Items] |  |  |
Fair value of securities on deposit with various regulatory authorities | $ 11 |  | $ 11
Number of securities in unrealized loss position for a continuous 12 month period | Security | 433 |  | 450
Rate that a security's fair value is below book value | 5.00% |  | 5.00%
Increase decrease in other net realized (gains) losses | $ (2) | $ 15 |
Asset Pledged as Collateral [Member] |  |  |
Schedule Of Investments [Line Items] |  |  |
Fair value of securities pledged as collateral | $ 230 |  | $ 241
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
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 |  | 365

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