Report of time spent on a customer and the task associated with it

Report of time spent on a customer and the task associated with it

I would like to create a report to show the time spent on a customer. 
I want that the time to be taken from Calls Duration and the Meetings held with the customer. 
Additionally, I would like to include all the tasks related to the customer. 

We are looking to determine how much of our employee's time is spent on each customer.