If you "print itinerary" one by one you should get a nice summary, one page per trip.

If you try to print all at once from "my trips" you only see information on the outbound flights. Here, like many places on the delta.dumb, printing it in landscape rather than portrait helps to keep the font size large enough to read, but I still like to do print preview on IE and adjust the size so that the columns I need take the whole width of the page.