Investments (Summary of Allowance for Credit Losses on AFS Investments) (Detail) - Accounting Standards Update 2016-13 [Member] $ in Millions	3 Months Ended
Mar. 31, 2022 USD ($)
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Beginning Balance	$ 0
Additions not previously recorded	3
Additions arising from PCD Assets	0
Reductions from Securities Sold	0
Reductions – Intent to sell or MLTN	0
Change in Allowance Previously Recorded	0
Write- Offs	0
Recoveries	0
Ending balance	3
Corporate Obligations [Member]
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Beginning Balance	0
Additions not previously recorded	3
Additions arising from PCD Assets	0
Reductions from Securities Sold	0
Reductions – Intent to sell or MLTN	0
Change in Allowance Previously Recorded	0
Write- Offs	0
Recoveries	0
Ending balance	$ 3

Amount of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=124269663&loc=SL82922900-210455

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 9
-Subparagraph (i)
-URI https://asc.fasb.org/extlink&oid=124269663&loc=SL82922900-210455

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aaa)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563

Reference 4: 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

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Amount of expense for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), for which no credit loss was previously recorded.

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Amount of expense (reversal of expense) for allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), not intended to be sold and not more likely than not will be required to sell before recovery of amortized cost basis, with previously recorded allowance.

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Amount of writeoff of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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