Coming from the fee for service world I am very familiar with how hard it is to calculate every little thing you do. It is even hard sometimes just to tell people what it is that you do on a daily basis. This would be considered your processes and procedures. It's always good to document these things to assist in relaying this information to designated staff.
You can start to gather information for this document by simply writing down what you do from the minute you put down your coat and or bag, until you pick them up to leave work for the day. (For my work from home folk, write from your first email until your last call of the day).
Don't feel pressured to finish this document all in 1 day. It could take a week or more to collect all the essential things you need to give to someone to effectively do what you do.