Long-duration insurance contracts - Narrative (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Liability for Future Policy Benefit, Activity [Line Items]
Guaranteed minimum death and living benefits associated with variable annuity products liability	$ 895	$ 1,250
Reduction in liability for effects of changes in securities markets interest rates and other inputs	$ 316