Amount of allowance for credit loss for debt security measured at amortized cost (held-to-maturity).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Amount of increase (decrease) in allowance for credit loss on investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
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Amount of increase in allowance for credit loss on investment in debt security measured at amortized cost (held-to-maturity), from recovery.

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Investments (Rollforward of expected credit losses HTM) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss	$ 44		$ 0
Debt Securities, Held-to-maturity, Allowance for Credit Loss, Period Increase (Decrease)	9
Debt Securities, Held-to-maturity, Allowance for Credit Loss, Recovery	$ (9)
Accounting Standards Update 2016-13 [Member]
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss		$ 44