A document is only deletable in its parent content listing.
If you want to see the document to be sure it's the one to delete, you have to go back to the parent listing view and then delete it.
Add a delete / move to trash button in the main action list in the document. Once on the document you should be able to delete it and fall back on its parent.
This action will be also useful when viewing a Collection => ability to delete the collection while checking the content.
Also useful for Templates.