According to benes' stickied A/V specifications thread, Darkman's TrueHD track is 24-bit. However, High-Def Digest reports it as 16-bit. I would trust benes more, as he uses computer software for his bit-rate readouts. But then again, Darkman is an older film from 1990, so I could see the original master being 16-bit.
It's worth noting that High-Def Digest also reports Notting Hill as having a 16-bit TrueHD track. That site does often get audio specs wrong, so I would like to know where they get their information from.