As long as:
- your layover doesn't exceed 24 hours;
- you don't have to pick up your luggage (ie you're flying with either one airline, or 2 airlines that interline; or don't have check-in luggage):
- don't have to change terminals
You don't need a transit visa. Having the details of your flights would, as jcaron says, help.
I have a fair bit of experience transferring at KLIA, usually on 2 separate tickets, and the transfer desks staff are very efficient and helpful, albeit a bit cold. I always drop by the counter, even when I have my 2 boarding passes, to make sure the luggage is on its way. Saved my bacon a couple of times.
14 hours in KLIA is going to be a long wait. The airport is cold in all the meanings of the word. There isn't much to do there, and the seats are not very comfortable. It's designed to shuttle people around efficiently, but not really to keep them entertained... A very different approach from nearby Singapore.