Investments in fixed maturity securities - Amortized cost and estimated fair value of securities with fixed maturities (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Summary of Investment Holdings [Line Items]
Due in one year or less - amortized cost	$ 18,888
Due after one year through five years - amortized cost	3,744
Due after five years through ten years - amortized cost	611
Due after ten years - amortized cost	128
Amortized cost of mortgage-backed securities	154
Amortized cost of fixed maturity securities	23,525	$ 25,173
Due in one year or less - fair value	18,875
Due after one year through five years - fair value	3,754
Due after five years through ten years - fair value	823
Due after ten years - fair value	138
Fair value of mortgage-backed securities	168
Fair value of fixed maturity securities	$ 23,758	$ 25,128