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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 $ in Millions | Mar. 31, 2023 USD ($) security
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> 5% To 15% [Member] |
Available For Sale Securities [Abstract] |
Number of securities | security | 213
Book Value | $ 427
Fair Value | $ 384
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 | 145
Book Value | $ 297
Fair Value | $ 241
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 | 84
Book Value | $ 132
Fair Value | $ 91
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 | 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] |
Available For Sale Securities [Abstract] |
Number of securities | security | 444
Book Value | $ 856
Fair Value | $ 716

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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(6)) -URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 45 -Paragraph 1 -URI https://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=124260329&loc=d3e26610-111562 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aa) -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563 + Details
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