Investments in fixed maturity securities - Amortized cost and estimated fair value of securities with fixed maturities (Detail) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Summary of Investment Holdings [Line Items]
Due in one year or less - amortized cost	$ 15,632
Due after one year through five years - amortized cost	5,748
Due after five years through ten years - amortized cost	708
Due after ten years - amortized cost	136
Amortized cost of mortgage-backed securities	172
Amortized cost of fixed maturity securities	22,396	$ 25,173
Due in one year or less - fair value	15,452
Due after one year through five years - fair value	5,654
Due after five years through ten years - fair value	916
Due after ten years - fair value	145
Fair value of mortgage-backed securities	186
Fair value of fixed maturity securities	$ 22,353	$ 25,128