U.S. stocks on Wednesday mostly held on to their gains in volatile trade, as Wall Street digested the implications of the Federal Reserve's supersized 50 basis point rate cut and its signal that more easing was ahead.

The Federal Reserve is expected to cut its influential fed funds rate in its September meeting. But economists and market watchers are waiting to know by how much.

The Federal Open Market Committee voted Wednesday to lower interest rates by 50 basis points, bringing the federal funds rate down from two-decade highs after more than a year of watching and waiting.