Investments in fixed maturity securities (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	$ 23,525	$ 25,173
Unrealized gains on fixed maturity securities	334	395
Unrealized losses on fixed maturity securities	(101)	(440)
Fair value of fixed maturity securities	23,758	25,128
U.S. Treasury, U.S. government corporations and agencies [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	10,308	10,039
Unrealized gains on fixed maturity securities	14	12
Unrealized losses on fixed maturity securities	(53)	(249)
Fair value of fixed maturity securities	10,269	9,802
Foreign governments [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	11,788	10,454
Unrealized gains on fixed maturity securities	58	50
Unrealized losses on fixed maturity securities	(41)	(177)
Fair value of fixed maturity securities	11,805	10,327
Corporate bonds [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	1,212	1,945
Unrealized gains on fixed maturity securities	241	256
Unrealized losses on fixed maturity securities	(4)	(6)
Fair value of fixed maturity securities	1,449	2,195
Other [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	217	2,735
Unrealized gains on fixed maturity securities	21	77
Unrealized losses on fixed maturity securities	(3)	(8)
Fair value of fixed maturity securities	$ 235	$ 2,804