Investors do not expect the central bank to increase interest rate in the meeting but will closely watch Fed Chair Janet Yellen's views on inflation, which remains stuck below the Fed's 2-percent target rate.
Nasdaq 100 e-minis were up 0.75 points, or 0.01 percent, in volume of 29 contracts.
At 11:00 a.m. ET (1500 GMT), the Dow Jones Industrial Average was up 16.16 points, or 0.07 percent, at 22,347.51, the S&P 500 was up 0.32 points, or 0.01 percent, at 2,504.19 and the Nasdaq Composite was up 2.42 points, or 0.04 percent, at 6,457.05.
The Nasdaq Composite .IXIC added 6.68 points, or 0.1 percent, to 6,461.32, also squeaking out a record closing high, slightly above its September 13 close.
Any reduction in the balance sheet could make it harder for banks and investors to borrow certain Treasuries in the repurchase agreement market, making it more difficult and expensive to bet on or protect against interest rate increases.
The three major USA stock indexes closed at record highs on Tuesday, with the financial stocks providing the biggest boost.
Analysts said market will also be looking for clues of whether the Fed will raise rates in December.
The Fed committed to reducing the bonds they own at a pace of $10 billion a month and increasing that pace by $10 billion every three months to a maximum pace of $50 billion a month, or $600 billion a year.More news: Hurricane Maria Brought A 'Mind Boggling' Amount Of Destruction To Dominica
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Several central-bank officials already wanted to start winding down the Fed's portfolio of government securities in July, but the majority wanted to hold until a later date.
However, the biggest determinant of a rate hike in December will be how the equity and bond markets react to the reduction of the Fed's bond portfolio, said Frederick.
On the other hand, gold stocks fell sharply following the Fed announcement, dragging the NYSE Arca Gold Bugs Index down by 1.9%.
JPMorgan Chase (JPM) advanced 1.2% and Goldman Sachs (GS) increased 1% to be among the top gainers on the Dow.
Alnylam Pharmaceuticals ( ALNY ) is posting a substantial gain after the biopharmaceutical company reported positive trial results for its treatment of a rare genetic disease.
Bed Bath & Beyond Inc.(BBBY) slumped almost 16%, marking its lowest close since 2009 and its second-worst drop on record, according to WSJ Market Group Data, after the retailer late Tuesday released earnings that widely missed forecasts (http://www.marketwatch.com/story/bed-bath-beyond-earnings-miss-widely-stock-halted-2017-09-19).
Oil prices clung to gains with a barrel of crude rose two cents at $49.91.