Long-duration insurance contracts - Summary of Other Information Relating to Long-Duration Insurance Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Annuities [Member]
Liability for Future Policy Benefit, Activity [Line Items]
Undiscounted expected future benefits	$ 30,592	$ 31,066
Weighted average discount rate	5.80%	5.10%
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	$ 100,413	$ 117,078
Discounted expected future gross premiums	58,881	66,692
Undiscounted expected future benefits	$ 91,493	$ 111,630
Weighted average discount rate	4.90%	5.10%
Weighted average accretion rate	2.70%	3.30%
Weighted average duration (in years)	13 years	13 years