Whenever you place a dimension on the Rows or Columns shelf, Tableau uses the categorical members of the dimension to create table headers. The headers show how Tableau is sorting the underlying row data into specific categories. For example, the Customer Segment dimension separates the data source rows into four levels of detail: Consumer, Corporate, Home Office, and Small Business.
Drop a dimension on the Detail target on the Marks card to separate the marks in a data view according to the members of a dimension. Unlike dropping a dimension on the Rows or Columns shelf, dropping it on the Detail target is a way to show more data without changing the table structure.
In the view below, the bars are separated into segments according to the members of the Category dimension. The size of each segment reflects the contribution to the profit for a particular member. For example, the Appliances category in the Corporate market has a profit of $71,392.
You can place any number of dimensions on the Detail target. In fact, placing all dimensions on this shelf is one way to display all the rows of your data source.
The Detail property works only if the measures that contribute axes to the table are aggregated. If the measures are disaggregated, then it isn't possible to separate the marks into additional levels of detail because all levels of detail are already shown.
Placing a measure on Detail has no effect because measures do not contain members. However, you can place measures on this shelf if you want to export their values to Microsoft Access, copy their values to the Clipboard, or use the values in actions.