Not since the beginning, but 400 years after Christ, written in creeds. The early Fathers certainly didn’t hold such doctrine, it’s not scriptural.
If you want to point out references of them being of one substance, I will yield.
Oh, and what exactly makes one different Christian doctrine ok, but other different Christian doctrines a bad thing? There are 30 thousand different Christian denominations, teaching different doctrines. Is the “trinity” the one sure doctrine and all else doesn’t matter? You seem to not have any problem with the other religions that teach different things.