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Long-duration insurance contracts - Summary of Other Information Relating to Long-Duration Insurance Liabilities (Detail) - USD ($) $ in Millions | Mar. 31, 2024 | Mar. 31, 2023
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Periodic Payment Annuity [Member] |  |
Liability for Future Policy Benefit, Activity [Line Items] |  |
Undiscounted expected future benefits | $ 30,953 | $ 31,244
Weighted average discount rate | 5.40% | 5.00%
Weighted average accretion rate | 4.80% | 4.80%
Weighted average duration (in years) | 17 years | 18 years
Life and Health [Member] |  |
Liability for Future Policy Benefit, Activity [Line Items] |  |
Undiscounted expected future gross premiums | $ 95,514 | $ 107,831
Discounted expected future gross premiums | 56,585 | 64,421
Undiscounted expected future benefits | $ 86,800 | $ 102,881
Weighted average discount rate | 4.90% | 4.90%
Weighted average accretion rate | 2.70% | 3.20%
Weighted average duration (in years) | 13 years | 14 years

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