This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
Koichi has a one-hundred-million yen condo in Tokyo.
I can't believe that Japan, a tiny island country, has one hundred million people living on it.
I won a hundred million dollars in the lottery, but I donated it all to charity because I’m a trillionaire.