US stocks fell, erasing small gains at the open today, as investors grappled with a move by the Swiss National Bank to scrap its three-year euro cap on the franc. Trading was likely to remain volatile through the session, on the heels of choppy premarket action that saw futures fluctuate between gains and losses, after the SNB said it would discontinue the cap it introduced on September 6, 2011 to fight recession and deflation threats.