But it left interest rates unchanged.
The main US share indexes fell from earlier peaks with the Dow Jones still closing at record high up 96.49 points or 0.45% at 21,709.92.
The wider S&P 500 closed up 0.69 points or 0.03% at 2,477.82 while the tech-focused Nasdaq index ended 10.57 points or 0.16% ahead at 6,422.75.
The Federal Reserve said in its statement on Wednesday that it would start cutting back its $4.5tn balance sheet "relatively soon".
In June it had suggested it would start "this year".
Chris Low, chief economist at FTN Financial in New York said: "The Fed did the bare minimum today, acknowledging recent economic data and little else.
"Balance sheet reduction will likely be announced at the September meeting and begin soon after.
"The next rate hike, therefore, is not likely to be considered until December."
Earlier shares were boosted as investors welcomed some strong trading updates.
Boeing shares jumped more than 9% after the firm's quarterly profits beat expectations.
The US aerospace giant also said it expects higher profits for the year than previously forecast.
Second quarter earnings have continued to beat analyst expectations.
Shares at AT&T climbed more than 5% on Wednesday, a day after that the telecommunications giant told investors that it had lowered operating costs and was holding onto customers better.
Not all the corporate news was welcomed though.
Ford shares fell 1.8%, after the US carmaker reported nearly flat revenues for the quarter and warned investors that key markets, including North America and Europe, would be less profitable this year than last.
The Federal Reserve signalled it could be ready to start unwinding its stimulus programme sooner than previously expected.