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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) - Unrealized loss position > 12 months [Member] $ in Millions | Sep. 30, 2023 USD ($) Security
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> 5% To 15% [Member] |
Available For Sale Securities [Abstract] |
Number of securities | Security | 194
Book Value | $ 336
Fair Value | $ 304
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] |
Available For Sale Securities [Abstract] |
Number of securities | Security | 153
Book Value | $ 386
Fair Value | $ 309
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] |
Available For Sale Securities [Abstract] |
Number of securities | Security | 159
Book Value | $ 373
Fair Value | $ 244
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] |
Available For Sale Securities [Abstract] |
Number of securities | Security | 3
Book Value | $ 5
Fair Value | $ 2
Held To Maturity Securities [Abstract] |
Percentage Of Fair Value Below Book Value Minimum | 50.00%
Greater Than 5% [Member] |
Available For Sale Securities [Abstract] |
Number of securities | Security | 509
Book Value | $ 1,100
Fair Value | $ 859

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