Investments in fixed maturity securities (Detail) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	$ 22,462	$ 25,173
Unrealized gains on fixed maturity securities	251	395
Unrealized losses on fixed maturity securities	(278)	(440)
Fair value of fixed maturity securities	22,435	25,128
U.S. Treasury, U.S. government corporations and agencies [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	9,663	10,039
Unrealized gains on fixed maturity securities	1	12
Unrealized losses on fixed maturity securities	(131)	(249)
Fair value of fixed maturity securities	9,533	9,802
Foreign governments [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	11,323	10,454
Unrealized gains on fixed maturity securities	43	50
Unrealized losses on fixed maturity securities	(130)	(177)
Fair value of fixed maturity securities	11,236	10,327
Corporate bonds [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	1,247	1,945
Unrealized gains on fixed maturity securities	190	256
Unrealized losses on fixed maturity securities	(12)	(6)
Fair value of fixed maturity securities	1,425	2,195
Other [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	229	2,735
Unrealized gains on fixed maturity securities	17	77
Unrealized losses on fixed maturity securities	(5)	(8)
Fair value of fixed maturity securities	$ 241	$ 2,804