Both Catholicism and Orthodoxy teach the eternal existence of the Holy Trinity, Spunkets.
Along with every major Protestant denomination.
A correct understanding of the Trinity is the foundation for any ecumenicism at all. Anyone who disavows the "eternal existence of the Holy Trinity" is not a member of the holy catholic church, as ordained by God for His glory.
But from various discussions on FR and in the news, it seems like the Trinity is going to be a battlefield of the 21st century. I appreciate the RCs and Orthodox holding firm to Scriptural orthodoxy here.