U.S. stocks soared Wednesday after the Federal Reserve surprised investors and analysts by extending rather than curtailing its unprecedented expansion of the money supply.

The S&P 500 index of large-capitalization stocks closed at a record high of 1725.52, while the Dow Jones Industrial Average of 30 blue-chip industrial stocks added 147,21 points to finish at a record 15,676.94.

The Fed's announcement Wednesday that it would not reduce its $85 billion-per-month purchases of Treasurys and mortgage-backed securities stunned Wall Street, which had thought the only question was whether the U.S. central bank would trim such purchases by $10 billion per month or $15 billion per month. The Fed's balance sheet is now approximately $3.66 trillion, more than it has ever been.

Treasury prices also climbed, as did gold -- up more than 4 percent -- and crude oil futures. The dollar fell to a nearly seven-month low against the euro.