Answer
The statement is correct.
Work Step by Step
Since the matrix $A$ is idempotent, then $A^{2}=A$.
Thus, we have:
$|A|=|A^{2}|=|AA|=|A||A|=|A|^{2}$
Therefore, we see that
$|A|(|A|-1)=0$
This indicates that either $|A|=0$ or $|A|=1$