YOU SAID:
You have no idea how rich he is
INTO JAPANESE
あなたは彼がどれほど裕福であるか知りません
BACK INTO ENGLISH
you don't know how rich he is
INTO JAPANESE
あなたは彼がどれだけ裕福か知りません
BACK INTO ENGLISH
you don't know how rich he is
That didn't even make that much sense in English.