WHERE did the idea of the trinity come from continued..?

Go to books.google.com and download "Bible Myths and Their Parallels in other Religions" by TW Doane. This text was used at Harvard Seminary, and explains how the bible was plagiarized from older myths. It has a whole chapter on the trinity, and the various older religions and their "Trinities" of gods and goddesses. For example, the Indian trinity of Brahman, Vishnu, and Siva.