Financial liabilities - Summary of Long Term Debt (Parenthetical) (Detail) - Long-term debt [Member]	12 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
US dollars [Member]
Disclosure of long term borrowings [Line Items]
Percentage of long term debt held based on currency	50.00%	53.00%
Euros [Member]
Disclosure of long term borrowings [Line Items]
Percentage of long term debt held based on currency	14.00%	13.00%
Japanese yen [Member]
Disclosure of long term borrowings [Line Items]
Percentage of long term debt held based on currency	12.00%	10.00%
Australian dollar [Member]
Disclosure of long term borrowings [Line Items]
Percentage of long term debt held based on currency	5.00%	5.00%
Canadian dollars [Member]
Disclosure of long term borrowings [Line Items]
Percentage of long term debt held based on currency	4.00%	4.00%
Other currencies [Member]
Disclosure of long term borrowings [Line Items]
Percentage of long term debt held based on currency	15.00%	15.00%
Unsecured loans principally from the bank [Member]
Disclosure of long term borrowings [Line Items]
Long term borrowings interest rate	3.56%	3.68%
Borrowings maturity	2025 to 2042	2024 to 2042
Secured loans (principally financial receivables securitization) [Member]
Disclosure of long term borrowings [Line Items]
Long term borrowings interest rate	4.23%	4.64%
Borrowings maturity	2025 to 2034	2024 to 2034
Unsecured bonds [Member] \| Parent [Member]
Disclosure of long term borrowings [Line Items]
Long term borrowings interest rate	1.93%	1.92%
Borrowings maturity	2026 to 2037	2024 to 2037
Secured bonds [Member] \| Consolidated subsidiaries [Member]
Disclosure of long term borrowings [Line Items]
Long term borrowings interest rate	8.12%	7.86%
Borrowings maturity	2025 to 2029	2024 to 2029
Unsecured Bonds and Medium Term Notes [Member] \| Consolidated subsidiaries [Member]
Disclosure of long term borrowings [Line Items]
Long term borrowings interest rate	3.61%	3.49%
Borrowings maturity	2025 to 2048	2024 to 2048