Investments in fixed maturity securities (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	$ 18,073	$ 19,427
Unrealized gains on fixed maturity securities	626	546
Unrealized losses on fixed maturity securities	(14)	(75)
Fair value of fixed maturity securities	18,685	19,898
U.S. Treasury, U.S. government corporations and agencies [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	3,054	4,223
Unrealized gains on fixed maturity securities	37	22
Unrealized losses on fixed maturity securities	(1)	(22)
Fair value of fixed maturity securities	3,090	4,223
Foreign governments [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	8,584	7,480
Unrealized gains on fixed maturity securities	63	50
Unrealized losses on fixed maturity securities	(9)	(28)
Fair value of fixed maturity securities	8,638	7,502
Corporate bonds [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	5,896	7,055
Unrealized gains on fixed maturity securities	459	408
Unrealized losses on fixed maturity securities	(3)	(23)
Fair value of fixed maturity securities	6,352	7,440
Other [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	539	669
Unrealized gains on fixed maturity securities	67	66
Unrealized losses on fixed maturity securities	(1)	(2)
Fair value of fixed maturity securities	$ 605	$ 733

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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