Long-duration insurance contracts - Summary of life, annuity and health insurance benefits liabilities (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Mar. 31, 2023
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Life, annuity and health insurance benefits	$ 17,987	$ 19,937
Periodic Payment Annuity [Member]
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Life, annuity and health insurance benefits	10,749	11,174
Life and Health [Member]
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Life, annuity and health insurance benefits	4,259	5,633
Other [Member]
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Life, annuity and health insurance benefits	$ 2,979	$ 3,130