According to Wikipedia Christianity can be divided in various ways. From a Catholic perspective the word "denomination" applies to Protestant groups while Catholics are part of different Rites, all in communion with the pope. But even the terminology is not universally accepted.
To answer the question I think we should refer to baptised Christians of all kinds as brother or sister in Christ (or simply as Christians) and focus on what we hold in common. Perhaps speaking of different "traditions" might be helpful, as we would to people of different cultural backgrounds. What annoys me is when Protestants suggest Catholics aren't Christians, something like saying women aren't part of mankind. We should all encourage better religious education - which would immediately put an end to the notion of idol worship by anybody.
