I am a long-tenured employee at my company and have become the subject matter expert for our business rules and the reasoning behind them. Additionally, I'm the last person around that knows the legacy systems which means I'm often the bottle neck for issues/questions and the first person who gets called if something goes wrong.
I want to start documenting all of this information so that my coworkers have access to the information they need and if I'm hit by a bus, operations can continue successfully. The things that need to be documented are a) hardware and software infrastructure and b) business rules and processes, so the format and process of collecting this disparate information may be different.
We currently use the Confluence wiki, so that seems like a good place for the documentation to live, but the body of knowledge is both wide and deep, so I'm looking for advice on processes or tools that I can use to get started.
EDIT: To address the (insightful) first comment. We are looking to replace a lot of the legacy system over the course of the next year, so the documentation I'm looking to create won't be so much a "living document" but an explanation of the current state so that the information lives somewhere other than just my head.