Well, I asked the guys and gals who invented English (who better to ask) what they thought the definition of the word ‘denomination’ was. Heres what they had to say:
n. name (particularly of a class of things); kind, class; religious sect
denomination

noun
a Christian denomination: RELIGIOUS GROUP, sect, cult, movement, body, branch, persuasion, order, school; Church
As you can see the word denomination includes in its definition ‘a branch’ or a class among classes. This word, ‘denomination’, is a deficient description for the Church, as, before protestantism existed there was only one Church. This One Church was not a branch or class of something else, related.
You must find a descriptive word for Catholicism which does not include that quality of being a branch or class.
Within Catholicism itself there are denominations, or orders, those
are branches of Catholicism, but Catholicism itself is not a branch of something else, as there was only Catholicism alone for the first three-quarters of the Churches 2000 year old history.