Investments in fixed maturity securities (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	$ 19,724	$ 18,073
Unrealized gains on fixed maturity securities	695	626
Unrealized losses on fixed maturity securities	(9)	(14)
Fair value of fixed maturity securities	20,410	18,685
U.S. Treasury, U.S. government corporations and agencies [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	3,348	3,054
Unrealized gains on fixed maturity securities	55	37
Unrealized losses on fixed maturity securities		(1)
Fair value of fixed maturity securities	3,403	3,090
Foreign governments [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	11,233	8,584
Unrealized gains on fixed maturity securities	110	63
Unrealized losses on fixed maturity securities	(5)	(9)
Fair value of fixed maturity securities	11,338	8,638
Corporate bonds [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	4,729	5,896
Unrealized gains on fixed maturity securities	464	459
Unrealized losses on fixed maturity securities	(2)	(3)
Fair value of fixed maturity securities	5,191	6,352
Other [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	414	539
Unrealized gains on fixed maturity securities	66	67
Unrealized losses on fixed maturity securities	(2)	(1)
Fair value of fixed maturity securities	$ 478	$ 605

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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