Long-duration insurance contracts - Summary of Other Information Relating to Long-Duration Insurance Liabilities (Detail) - USD ($) $ in Millions	Jun. 30, 2024	Jun. 30, 2023
Periodic Payment Annuity [Member]
Liability for Future Policy Benefit, Activity [Line Items]
Undiscounted expected future benefits	$ 30,867	$ 31,232
Weighted average discount rate	5.70%	5.30%
Weighted average accretion rate	4.80%	4.80%
Weighted average duration (in years)	16 years	18 years
Life and Health [Member]
Liability for Future Policy Benefit, Activity [Line Items]
Undiscounted expected future gross premiums	$ 94,942	$ 108,089
Discounted expected future gross premiums	55,787	65,599
Undiscounted expected future benefits	$ 86,253	$ 103,012
Weighted average discount rate	5.20%	5.00%
Weighted average accretion rate	2.70%	3.30%
Weighted average duration (in years)	13 years	14 years