I found the following quote referencing Gemara from a book on converts in Judaism:
The Gemara (Megillah 13•) states that we find the appellation “Yehudi” in Nach only three times: once for Mordechai (Ester 2:5); once for Chananiah, Mishael and Azariah (Daniel 3:12); and once for Basya the daughter of Pharaoh (Divrei Hayamim I 4:18). This title is given only to those Who rejected idolatry, for those who reject idolatry are called “Yehudi.”
The daughter of Pharaoh renounced her idolatrous background, and embraced Klal Yisrael, by converting.
So does one who reject idolatry become a Yahudi according to the Jews?