Investments in fixed maturity securities (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	$ 17,491	$ 18,073
Unrealized gains on fixed maturity securities	549	626
Unrealized losses on fixed maturity securities	(117)	(14)
Fair value of fixed maturity securities	17,923	18,685
U.S. Treasury, U.S. government corporations and agencies [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	3,314	3,054
Unrealized gains on fixed maturity securities	85	37
Unrealized losses on fixed maturity securities		(1)
Fair value of fixed maturity securities	3,399	3,090
Foreign governments [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	8,126	8,584
Unrealized gains on fixed maturity securities	75	63
Unrealized losses on fixed maturity securities	(47)	(9)
Fair value of fixed maturity securities	8,154	8,638
Corporate bonds [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	5,536	5,896
Unrealized gains on fixed maturity securities	317	459
Unrealized losses on fixed maturity securities	(67)	(3)
Fair value of fixed maturity securities	5,786	6,352
Other [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	515	539
Unrealized gains on fixed maturity securities	72	67
Unrealized losses on fixed maturity securities	(3)	(1)
Fair value of fixed maturity securities	$ 584	$ 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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