Bell Curve/Standard Deviation/Graph

Hello,

So I have a data set containing 5 company departments with each of their total spending per month for a whole year.

I am trying to set up a bell curve graph that shows the standard deviations/distribution of data so that it can easily be seen which departments have spending that is outside of, let's say, 3 standard deviations.

I just need some help setting up the chart and with ensuring that my calculations are correct.

I believe that I need to:
1) Calculate the average spending for the whole year for each department
2) Calculate the total average of the average department spends
3) Calculate the standard deviation of all the average spends for the departments
4) set up a Norm.Dist to calculate the distributions of each of the departments spending
5) set up a bell curve chart that shows the distribution of data and highlights which departments are outside of the normal deviations (e.g. spending way too much or way too little)

I believe I am on the right track but just need some help with the last several steps.

I've attached my excel sheet here which may better show the problem.

Any help would be appreciated! Thanks!