About a year ago, my employer asked me to take on a task so they wouldn't have to hire someone to do it. I did not get a raise for it. Basically, I'm given very vague details and have to type up a document to present to the client to review and either approve or point out things they'd like to change. Our employees then use the final, approved document during the course of the project as a reference. It's created a slew of issues over the year I've been doing it and since I was given no training, it involves a lot of extra work, headaches, and frustration. I'm tired of trying to pour over countless emails to find the most mundane details, tired of being the one to take the blame when something goes wrong with a project and it wasn't in the document. My job is otherwise very easy and since my personal life is very chaotic, I'd prefer to keep it that way. How do I tell my supervisor that I don't want to do it anymore without sounding as annoyed and resentful as I am?