Investments in fixed maturity securities (Detail) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	$ 15,214	$ 23,525
Unrealized gains on fixed maturity securities	257	334
Unrealized losses on fixed maturity securities	(107)	(101)
Fair value of fixed maturity securities	15,364	23,758
U.S. Treasury, U.S. government corporations and agencies [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	4,447	10,308
Unrealized gains on fixed maturity securities	16	14
Unrealized losses on fixed maturity securities	(4)	(53)
Fair value of fixed maturity securities	4,459	10,269
Foreign governments [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	9,443	11,788
Unrealized gains on fixed maturity securities	16	58
Unrealized losses on fixed maturity securities	(97)	(41)
Fair value of fixed maturity securities	9,362	11,805
Corporate and Other [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	1,324	1,429
Unrealized gains on fixed maturity securities	225	262
Unrealized losses on fixed maturity securities	(6)	(7)
Fair value of fixed maturity securities	$ 1,543	$ 1,684