Another interesting option with current promotional sale of Star Alliance airlines are round trip flights from Europe to Detroit. You may explore this city known as centre of heavy industry already from €312 when departing from Amsterdam, Italy or Paris. There is one short layover on your way in Frankfurt. (Flights are again based on United Airlines / Lufthansa).
Again to take the advantage of this current promotional offer of Lufthansa and United Airlines please look for flights departing between 12th of January and 9th of March 2016. Max stay 3 months and booking has to be done till 23rd of November 2015. Please refer to below booking sample from each of the origin countries:
At this moment you may find plenty of travel options in said travel period. If you would need to compare connection flight from your home town you may consider service of Skyscanner. Do not forget to issue US visa or ESTA certification prior departure.
Booking sample of cheap round trip flights from Europe to Detroit from €312! In this case you would be departing from Milan to Detroit on 27th of February. Your return flight from America back to Italy would be on 14th of March 2016.