Share based payment - Schedule of Movement of Options Outstanding under the share based payment schemes (Detail) - shares shares in Millions |
12 Months Ended | ||
|---|---|---|---|
Mar. 31, 2025 |
Mar. 31, 2024 |
Mar. 31, 2023 |
|
| 2021 Incentive Award Plan | |||
| Share Based Payment Arrangements [Line Items] | |||
| Outstanding at the beginning of the year | 51 | 36 | 30 |
| Granted during the year | 7 | 16 | 6 |
| Lapsed during the year | 1 | 1 | |
| Exercised/ lapsed during the year | 0 | ||
| Outstanding at the end of the year | 57 | 51 | 36 |
| Exercisable at the end of the year | 40 | 25 | |
| Holding Company Stock Option Plans | |||
| Share Based Payment Arrangements [Line Items] | |||
| Outstanding at the beginning of the year | 11 | 11 | 12 |
| Exercised/ lapsed during the year | 0 | 0 | 1 |
| Outstanding at the end of the year | 11 | 11 | 11 |
| Exercisable at the end of the year | 11 | 11 | |