Could you show a screen capture of what sort of text / "line item" information you want to retrieve, as shown in the OneStream client when you right-click on a cube view.
Do you mean Data Attachments, which is loosely what HFM used to call "line item detail"?
You also don't mention whether this needs to be done in a Finance BR, or an Extender rule ( the difference being whether we can use the Finance API methods or not ).
Assuming it is not in a Finance BR, then then you should be able to retrieve the text from the cell attachments list, like this:
Dim strMemberScript As String = String.Format("Cb#AUM:E#RevAccComments:C#Local:S#RevAccRecon:T#{0}:V#Annotation:A#MGMTFEES:F#CQ_MGMT_FEE_REV:O#Forms:I#None:U1#None:U2#None:U3#None:U4#{1}:U5#None:U6#None:U7#None:U8#None", FYQ, strU4ProdName)
Dim sbCellTexts As New Text.StringBuilder()
Dim lstAttachements As DataAttachmentList = brapi.Finance.Data.GetDataAttachments(si, strMemberScript, False)
For Each attachment As DataAttachment In lstAttachements.Items
If Attachment.Text IsNot Nothing Then
sbCellTexts.AppendLine(Attachment.Title & " / " & Attachment.Text)
End If
Next
BRApi.ErrorLog.LogMessage(si,"Retrived all the text items from cell:", sbCellTexts.ToString() )