In god theory how is it that all protestants profess to a fourth century catholic belief in trinity?

The Trinity is One. We do not confess three Gods, but one God in three persons , the ˜consubstantial Trinity.' The divine persons do not share the one divinity among themselves but each of them is God whole and entire. The Father is that which the Son is, the Son is that which the Father is, the Father and the Son that which the Holy Spirit is, i.e. by nature one God. (From catholic catechism)