Five. (20 points) Let
$$
f(x)=\ln x-\frac{1}{2} a x^{2}-2 x \quad (a<0),
$$

and the function $f(x)$ has a monotonically decreasing interval.
(1) Find the range of values for $a$;
(2) If for any value of $a$ that satisfies the condition, $f(x)<b$ holds for all $x \in (0,1]$, find the range of values for the real number $b$.