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Investments (Distribution Of Securities By Percentage Of Fair Value Below Book Value By More Than 5% For A Continuous Twelve Month Period Or Longer) (Detail) $ in Millions | Mar. 31, 2024 USD ($) Security | Dec. 31, 2023 USD ($)
--- | --- | ---
Available For Sale Securities [Abstract] |  |
Book Value | $ 1,544 |
Fair Value | $ 1,397 | $ 1,557
> 5% To 15% [Member] | Unrealized loss position > 12 months [Member] |  |
Available For Sale Securities [Abstract] |  |
Number of securities | Security | 176 |
Book Value | $ 231 |
Fair Value | $ 208 |
Held To Maturity Securities [Abstract] |  |
Percentage Of Fair Value Below Book Value Minimum | 5.00% |
Percentage Of Fair Value Below Book Value Maximum | 15.00% |
> 15% To 25% [Member] | Unrealized loss position > 12 months [Member] |  |
Available For Sale Securities [Abstract] |  |
Number of securities | Security | 108 |
Book Value | $ 277 |
Fair Value | $ 226 |
Held To Maturity Securities [Abstract] |  |
Percentage Of Fair Value Below Book Value Minimum | 15.00% |
Percentage Of Fair Value Below Book Value Maximum | 25.00% |
> 25% To 50% [Member] | Unrealized loss position > 12 months [Member] |  |
Available For Sale Securities [Abstract] |  |
Number of securities | Security | 79 |
Book Value | $ 227 |
Fair Value | $ 152 |
Held To Maturity Securities [Abstract] |  |
Percentage Of Fair Value Below Book Value Minimum | 25.00% |
Percentage Of Fair Value Below Book Value Maximum | 50.00% |
> 50% [Member] | Unrealized loss position > 12 months [Member] |  |
Available For Sale Securities [Abstract] |  |
Number of securities | Security | 2 |
Book Value | $ 0 |
Fair Value | $ 0 |
Held To Maturity Securities [Abstract] |  |
Percentage Of Fair Value Below Book Value Minimum | 50.00% |
Greater Than 5% [Member] | Unrealized loss position > 12 months [Member] |  |
Available For Sale Securities [Abstract] |  |
Number of securities | Security | 365 |
Book Value | $ 735 |
Fair Value | $ 586 |

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