Investments in fixed maturity securities - Narrative (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2023	Dec. 31, 2022
Summary of Investment Holdings [Line Items]
Fair value of fixed maturity securities	$ 22,353	$ 25,128
US Treasury Securities [Member]
Summary of Investment Holdings [Line Items]
Fair value of fixed maturity securities	$ 8,300
Fixed maturity securities, maturity year	2023 and 2024
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%