Summary of material accounting policies - Disclosure of estimated useful lives of intangible assets (Details) |
12 Months Ended |
|---|---|
Sep. 30, 2025 | |
| Minimum | Software internally developed | |
| Disclosure of detailed information about intangible assets [line items] | |
| Estimated useful life | 1 year |
| Minimum | Business solutions | |
| Disclosure of detailed information about intangible assets [line items] | |
| Estimated useful life | 3 years |
| Minimum | Client relationships and backlog | |
| Disclosure of detailed information about intangible assets [line items] | |
| Estimated useful life | 5 years |
| Maximum | Software internally developed | |
| Disclosure of detailed information about intangible assets [line items] | |
| Estimated useful life | 8 years |
| Maximum | Business solutions | |
| Disclosure of detailed information about intangible assets [line items] | |
| Estimated useful life | 10 years |
| Maximum | Client relationships and backlog | |
| Disclosure of detailed information about intangible assets [line items] | |
| Estimated useful life | 10 years |