Long-duration insurance contracts - Summary of gross premiums earned and net interest expense (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Periodic Payment Annuities [Member]
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums		$ 529
Net Interest Expense	$ 402	404
Life and Health [Member]
Liability for Future Policy Benefit, Activity [Line Items]
Gross Premiums	2,587	2,700
Net Interest Expense	$ 163	$ 159