Investments in fixed maturity securities (Detail) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	$ 17,602	$ 19,724
Unrealized gains on fixed maturity securities	551	695
Unrealized losses on fixed maturity securities	(28)	(9)
Fair value of fixed maturity securities	18,125	20,410
U.S. Treasury, U.S. government corporations and agencies [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	3,358	3,348
Unrealized gains on fixed maturity securities	30	55
Fair value of fixed maturity securities	3,388	3,403
Foreign governments [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	12,407	11,233
Unrealized gains on fixed maturity securities	38	110
Unrealized losses on fixed maturity securities	(27)	(5)
Fair value of fixed maturity securities	12,418	11,338
Corporate bonds [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	1,510	4,729
Unrealized gains on fixed maturity securities	431	464
Unrealized losses on fixed maturity securities		(2)
Fair value of fixed maturity securities	1,941	5,191
Other [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	327	414
Unrealized gains on fixed maturity securities	52	66
Unrealized losses on fixed maturity securities	(1)	(2)
Fair value of fixed maturity securities	$ 378	$ 478

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) 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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Amortized cost of 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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