Add a Details Group (Report Builder and SSRS)
The detail data from a report dataset is specified as a group with no group expression. Add a detail group to an existing tablix data region when you want to display the detail data for a matrix, add back detail data that you have deleted from a table or list, or to add additional detail groups. For more information about groups, see Understanding Groups (Report Builder and SSRS).
You can create and modify report definitions (.rdl) in Report Builder and in Report Designer in SQL Server Data Tools. Each authoring environment provides different ways to create, open, and save reports and related items. For more information, see Designing Reports in Report Designer and Report Builder (SSRS) on the Web at microsoft.com.
To add a details group to a tablix data region
On the design surface, click anywhere in a tablix data region to select it. The Grouping pane displays the row and column groups for the selected data region.
In the Grouping pane, right-click a group that is an innermost child group. Click Add Group, and then click Child Group. The Tablix Group dialog box opens.
In Group expression, leave the expression blank. A details group has no expression.
Select Show detail data.
A new details group is added as a child group in the Grouping pane, and the row handle for the group you selected in step 1 displays the details group icon. For more information about handles, see Tablix Data Region Cells, Rows, and Columns (Report Builder) and SSRS.