How to: Add a Details Group (Reporting Services)
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 (Reporting Services).
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 Understanding Tablix Data Region Cells, Rows, and Columns.