Black disc hovers floats while spinning forward over and over again - looks like plate or garbage can lid caught in a weird wind gust

It was 4th of july and I was watching fireworks on my front porch. Across from us was an apartment building and off to the left of that building I saw a dark disc shape hovering and flipping forward, very slowly. It looked like if a paper plate was caught in a strange wind gust. But it had more weight than a plate. It hovered there and started to slowly drift out of sight, in the way that a balloon would when released, but slower.
 This thing had to be at least the size of an apartment window. But I couldn't tell if it was low and near the edge of building, or if it was huge, and the angle I viewed it made it seem closer.
 This is the only crazy thing to happen in my life. I remember it clear as day. This was before drones or the thought of one, but theres no way this could be that.
 My thoughts:  a craft that is like a smooth rounded coin, that can flip in any direction it wants to fly in strange angles or speeds. The key thing is that the fireworks were off to one side and this thing was on another side. I watched it as it floated told my Dad to look and he didn't see it, but I did it and just got further away.
 1000% truth this happened exactly as I say it did. It could be summer '88 or summer '90, over bensonhurst/Brooklyn area.