| Label | Element | Value |
|---|---|---|
| Risk/Return: | rr_RiskReturnAbstract | |
| Document Type | dei_DocumentType | 485BPOS |
| Document Period End Date | dei_DocumentPeriodEndDate | Nov. 30, 2017 |
| Registrant Name | dei_EntityRegistrantName | VANGUARD CONVERTIBLE SECURITIES FUND |
| Central Index Key | dei_EntityCentralIndexKey | 0000791107 |
| Amendment Flag | dei_AmendmentFlag | false |
| Document Creation Date | dei_DocumentCreationDate | Mar. 27, 2018 |
| Document Effective Date | dei_DocumentEffectiveDate | Mar. 27, 2018 |
| Prospectus Date | rr_ProspectusDate | Mar. 27, 2018 |