No need to put anything in the detail section. Just suppress it.
Group1=Department Field
Only display the Group name on GH1
Group2=User Field
click on the Insert SUmmary button (Sigma Sign/looks like an E)
Field to Summarize=Total (assuming this is numeric)
Calculate as: SUM
Summary Location = Group 2
Hit OK
YOu will see a new field appear on group footer 2. MOve this to Group Header 2 next to the group 2 name
SUppress Details and group footers as you desire