I've seen them once, just as you describe them, over the Detroit area. Disregarding the "contrails", what I found odd was the flight pattern....all due east and west, and pretty evenly spaced north to south.....not at all the normal flight paths for airliners I normally see from here. The day that I saw this was in November. Never before or since.
East-West flights were at the right altitude to be making contrails. That's not so odd.