Let $A$ be a $4 \times 4$ block matrix of the form $A = \begin{pmatrix} P & Q \\ 0 & R \end{pmatrix}$ where $P$ and $R$ are $2 \times 2$ blocks with $\det(P) = 3$ and $\det(R) = -2$, and $Q$ is an arbitrary $2 \times 2$ block. What is $\det(A)$?