Investments in fixed maturity securities - Narrative (Detail) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Summary of Investment Holdings [Line Items]
Fair value of fixed maturity securities	$ 22,435	$ 25,128
Fair values of fixed maturity securities that mature within next twelve months	17,261
US and Foreign government [Member]
Summary of Investment Holdings [Line Items]
Fair values of fixed maturity securities that mature within next twelve months	$ 17,200
Foreign governments [Member] | AA or Higher Credit Rating [Member]
Summary of Investment Holdings [Line Items]
Percentage of fixed maturity investments by credit rating	94.00%