It is commonly and popularly known as idli only. The pronunciation may change according to regions like Sun has said it is ittili and in Kerala it is called iddali. So it depends like how people from different regions call it or pronounce it as is the case for so many other things. There may be areas where people call it as idhuli, who knows?
If we begin to entertain such doubts and ask questions based on names and pronunciations, I am sure that we would have so many in the genre!
'Knowing others is wisdom, knowing yourself is Enlightenment'- Lao Tzu