Stocks are flat ahead of the Fed's statement

US stocks opened slightly lower on Wednesday as traders paused the so-called Trump rally ahead of the Federal Reserve's policy statement.

The Dow closed at an all-time high on Tuesday - its 16th since the election. Although it missed the 20,000 mark, the S&P 500 quietly hit another milestone: Bespoke Investment Group noted that members' market cap crossed $20 trillion for the first time.

While the Federal Open Markets Committee is widely expected to raise interest rates, the Fed's guidance for future policy and its forecasts for economic growth could be news to markets. During her press conference, Chair Janet Yellen's may speak on how the Fed is viewing the upside potential - and uncertainty - of economic growth that the new administration's fiscal policy plans could bring.

The other economic data released on Wednesday were mixed. Retail sales rose 0.1% (0.3% forecast) in November. Industrial production declined by 0.4% in November, while producer prices reported their largest gain in five months.