Not only does UA and every other airline tell you during the booking process that YOU, the passenger, are responsible for making sure you have the correct documents, they also provide a tool to let YOU, the passenger, find what you need to have. Pay special attention to the last part of the "Itinerary Details" that YOU, the passenger, provide where it says, "Transit Point 1"
http://www.united.com/web/en-us/apps...aspx?i=TIMATIC