The first three digits of an Id is an identifier to the type of entity that the object is. It doesn’t matter if the Id is a 15 digit or 18 digit id.
| SObject | ID Prefix |
|---|---|
| Account | 001 |
| Case | 500 |
| Contact | 003 |
| Lead | 00Q |
| Opportunity | 006 |
| Task | 00T |
Standard Salesforce Object Id Prefixes
