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v3.25.1

Investments (Narrative) (Detail) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2025 USD ($) Security | Mar. 31, 2024 USD ($) | Dec. 31, 2024 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 | 304 |  | 366
Rate that a security's fair value is below book value | 5.00% |  | 5.00%
Increase decrease in other net realized (gains) losses | $ (7) | $ (3) |
Asset Pledged as Collateral [Member] |  |  |
Schedule Of Investments [Line Items] |  |  |
Fair value of securities pledged as collateral | $ 212 |  | $ 213
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 |  | 15 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 | 244 |  | 318

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