Investments in fixed maturity securities - Amortized cost and estimated fair value of securities with fixed maturities (Detail) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Summary of Investment Holdings [Line Items]
Due in one year or less - amortized cost	$ 10,272
Due after one year through five years - amortized cost	10,456
Due after five years through ten years - amortized cost	443
Due after ten years - amortized cost	92
Amortized cost of fixed maturity securities	21,485	$ 15,964
Due in one year or less - fair value	10,250
Due after one year through five years - fair value	10,370
Due after five years through ten years - fair value	734
Due after ten years - fair value	112
Fair value of fixed maturity securities	21,718	$ 16,434
Mortgage-backed securities [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of mortgage-backed securities	222
Fair value of mortgage-backed securities	$ 252