Im an Italian citizen living in the USA.?
All EU citizens can travel to all other EU countries using only their national identity cards: there is no need for a passport. At the time of writing (7 April) the UK is part of the EU. The date on which the UK leaves is not clear, although it is unlikely that we will actually leave on 12 April, the most recent date agreed. Nor is it clear what travel arrangements will be in force between the UK and the EU shortly afterwards. The bottom line is that an Italian identity card will always allow you to travel to Italy, but might not be valid for entering the UK once the UK has left.