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Long-duration insurance contracts - Summary of Other Information Relating to Long-Duration Insurance Liabilities (Detail) - USD ($) $ in Millions | Dec. 31, 2024 | Dec. 31, 2023
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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

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