I presume that what you mean is that on your report you are aggregating the
data in your dataset, but would like the option of seeing all the detail that
makes up the aggregates. You could do this by:
a) Set up a boolean report parameter called HideDetail defaulting to =True.
b) Design your report with the detail lines and grouping. Make the detail
row's Hidden property =Parameters!HideDetail.Value. You could also set the
row's ToggleItem property to refer to one of the textboxes in your group
header/footer.

With this setup your report will not show detail lines by default. However,
you have the option to show the detail at run time by changing the HideDetail
report parameter to False.

HTH,
Magendo_man