Investments in fixed maturity securities (Detail) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	$ 22,396	$ 25,173
Unrealized gains on fixed maturity securities	320	395
Unrealized losses on fixed maturity securities	(363)	(440)
Fair value of fixed maturity securities	22,353	25,128
U.S. Treasury, U.S. government corporations and agencies [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	9,242	10,039
Unrealized gains on fixed maturity securities	2	12
Unrealized losses on fixed maturity securities	(192)	(249)
Fair value of fixed maturity securities	9,052	9,802
Foreign governments [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	11,571	10,454
Unrealized gains on fixed maturity securities	70	50
Unrealized losses on fixed maturity securities	(160)	(177)
Fair value of fixed maturity securities	11,481	10,327
Corporate bonds [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	1,333	1,945
Unrealized gains on fixed maturity securities	228	256
Unrealized losses on fixed maturity securities	(7)	(6)
Fair value of fixed maturity securities	1,554	2,195
Other [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	250	2,735
Unrealized gains on fixed maturity securities	20	77
Unrealized losses on fixed maturity securities	(4)	(8)
Fair value of fixed maturity securities	$ 266	$ 2,804