Updated from 4:21 p.m. EDTStocks in the U.S. ended marginally lower Tuesday as investors digested the latest round of earnings reports and positioned themselves ahead of the Federal Reserve's upcoming interest rate decision. The Dow Jones Industrial Average lost 77.79 points, or 0.56%, to 13,792.47, pulled down by a 4% drop in component Procter & Gamble ( PG). The S&P 500 was off 9.96 points, or 0.65%, at 1531.02. The Nasdaq Composite closed little changed, falling 0.73 point, or 0.03%, to 2816.71. The index was propped up by a 16.1% jump in Sepracor ( SEPR). While traders were certainly thinking about the Fed and the latest quarterly numbers from corporate America, the news of the day came from Merrill Lynch ( MER), which said embattled CEO Stan O'Neal has decided to leave the firm, effective immediately. Rumors of O'Neal's departure pushed the stock 10.7% higher over the previous two sessions, but shares of Merrill lost $1.86, or 2.8%, to $65.56 once the formal announcement came out. Elsewhere, the Federal Open Market Committee began its two-day meeting, with a decision about rates due at 2:15 p.m. EDT on Wednesday. Most economists are expecting a 25-basis-point cut, the second reduction in as many months after the Fed kept its fed funds target rate at 5.25% for nine straight meetings dating back to June 2006. "The market has been struggling, and the cyclical leadership stocks of late have been hit ahead of the Fed's rate meeting," said Phillip Roth, chief technical market analyst with Miller Tabak. "The question will be how the market responds to a Fed rate cut. We are expecting a 25-basis point cut and that's been discounted already. As soon as the Fed meeting comes and goes, traders will be waiting for the next data point."