Slow, low flying triangle with no sound

Traffic was very light on I-94 between Southfield and Telegraph.  I noticed cars approaching pulling off the road and was wondering why.  Then I happened to see it in the sky.  It moved very slowly, without sound.  It had to be at least as big as a football field and I pulled off to watch it about 1/4 mile ahead of me.  Once it had crossed the expressway I could see the back end and it was like a huge window all the way across.
There were no running lights, but the triangular shape was well defined by the moonlit sky.  This was less than 5 miles from Detroit Metro Airport and had to be flying very low because the incoming planes to the airport disappeared behind big triangle.  All in all I think there was 8-10 cars that pulled off the road to watch it.  It was reported in the Detroit newspapers because my girlfriend showed me the article the following day and she was amazed because the description matched my sketch.