If I publish an internal \wiki about what I do at work (IT department), will I become less indispensable?

I write manuals for everything that I do at work, but keep them to myself. This is so I don't forget how to do certain specific things. I keep them in wiki form and keep adding to it.

I'm thinking about publishing this in the larger context of a departmental knowledge base, and let people keep adding to it. In essence I would be giving specific knowledge to other people in the department about work that I do, however, it seems to me that IT people like to keep information to themselves in order to have competitive advantage. I'm not sure if that works, but it seems to be the norm.

Our management wishes we all had sort of the same skills (possibly to minimize risk if one employee is absent), but in reality, each one of the IT employees knows something that the other one doesn't.

Have you been in this situation? What do you recommend?