Investments in fixed maturity securities (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	$ 16,969	$ 23,525
Unrealized gains on fixed maturity securities	285	334
Unrealized losses on fixed maturity securities	(87)	(101)
Fair value of fixed maturity securities	17,167	23,758
U.S. Treasury, U.S. government corporations and agencies [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	4,517	10,308
Unrealized gains on fixed maturity securities	3	14
Unrealized losses on fixed maturity securities	(17)	(53)
Fair value of fixed maturity securities	4,503	10,269
Foreign governments [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	11,020	11,788
Unrealized gains on fixed maturity securities	39	58
Unrealized losses on fixed maturity securities	(62)	(41)
Fair value of fixed maturity securities	10,997	11,805
Corporate bonds [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	1,210	1,212
Unrealized gains on fixed maturity securities	224	241
Unrealized losses on fixed maturity securities	(5)	(4)
Fair value of fixed maturity securities	1,429	1,449
Other [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	222	217
Unrealized gains on fixed maturity securities	19	21
Unrealized losses on fixed maturity securities	(3)	(3)
Fair value of fixed maturity securities	$ 238	$ 235