Black equilateral triangle daytime

In a car waiting for a stop light. High in the sky was a Black equilateral triangle object lurking in a cloud. Saw it in a separation within the cloud. Partially cloudy day and sunny. Clouds at the time seemed to be mid level between 26,000 ft and 31,000 ft. Not a meteorologist just what I can guess from conditions at the time. The object was at the same level or slightly above. Object was a perfect triangle 60°x60x60 with no clear visible lights or markings; being that high up in the sky, there could have been. Based on altitude and how identified objects look like from the ground; estimated size was at least 1 1/2 times that of a Boeing 747. Object appeared motionless