The Dow Jones industrial average was down 65 points at 13,318 at midday Tuesday. The Standard & Poor's 500 index fell seven points to 1,453. The Nasdaq composite index fell 17 to 3,081.
Aluminum maker Alcoa becomes the first company in the Dow average to report earnings after the close of trading.
Other companies that have begun reporting turned in mixed results.
Yum brands, the parent company of KFC, Taco Bell and Pizza Hut, dropped after reporting problems with a chicken meat supplier.
Monsanto, an agricultural products maker, soared after reporting sharply higher earnings thanks to booming sales of crop seeds in Latin America.